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<rfc ipr="trust200902" docName="draft-ietf-bier-te-arch-13" category="std"> <rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902" docName="draft
<front> -ietf-bier-te-arch-13" number="9262" submissionType="IETF" category="std" consen
<title abbrev="BIER-TE ARCH">Tree Engineering for Bit Index Expl sus="true" obsoletes="" updates="" xml:lang="en" tocInclude="true" tocDepth="4"
icit Replication (BIER-TE)</title> symRefs="true" sortRefs="true" version="3">
<author role="editor" fullname="Toerless Eckert" initials="T.T.E
." surname="Eckert">
<organization abbrev="Futurewei">Futurewei Technologies Inc.</
organization>
<address>
<postal>
<street>2330 Central Expy</street>
<city>Santa Clara</city>
<code>95050</code>
<country>USA</country>
</postal>
<email>tte+ietf@cs.fau.de</email>
</address>
</author>
<author fullname="Michael Menth" initials="M.M." surname="Menth"
>
<organization>University of Tuebingen</organization>
<address>
<email>menth@uni-tuebingen.de</email>
</address>
</author>
<author fullname="Gregory Cauchie" initials="G.C." surname="Cauc
hie">
<organization>KOEVOO</organization>
<address>
<email>gregory@koevoo.tech</email>
</address>
</author>
<date month="April" year="2022"/>
<abstract>
<t> This memo describes per-packet stateless strict and loose path
steered replication and forwarding for "Bit Index Explicit Replication" (BIER, R
FC8279) packets. It is called BIER Tree Engineering (BIER-TE) and is intended t
o be used as the path steering mechanism for Traffic Engineering
with BIER.</t>
<t>BIER-TE introduces a new semantic for "bit positions" (BP). They indicate adj <!-- xml2rfc v2v3 conversion 3.12.2 -->
acencies <front>
of the network topology, as opposed to (non-TE) BIER in which BPs indicate <title abbrev="BIER-TE ARCH">Tree Engineering for Bit Index Explicit Replica
"Bit-Forwarding Egress Routers" (BFER). A BIER-TE packets BitString therefore tion (BIER-TE)</title>
indicates the <seriesInfo name="RFC" value="9262"/>
edges of the (loop-free) tree that the packet is forwarded across by BIER-TE. <author role="editor" fullname="Toerless Eckert" initials="T." surname="Ecke
BIER-TE can leverage BIER forwarding engines with little changes. rt">
Co-existence of BIER and BIER-TE forwarding in the same domain is possible, for <organization abbrev="Futurewei">Futurewei Technologies Inc.</organization
example by using >
separate BIER "sub-domains" (SDs). Except for the optional routed adjacencies, B <address>
IER-TE does not <postal>
require a BIER routing underlay, and can therefore operate without depending <street>2330 Central Expy</street>
on an "Interior Gateway Routing protocol" (IGP).</t> <city>Santa Clara</city>
</abstract> <code>95050</code>
</front> <region>CA</region>
<middle> <country>United States of America</country>
</postal>
<email>tte@cs.fau.de</email>
</address>
</author>
<author fullname="Michael Menth" initials="M." surname="Menth">
<organization>University of Tuebingen</organization>
<address>
<postal>
<country>Germany</country>
</postal>
<email>menth@uni-tuebingen.de</email>
</address>
</author>
<author fullname="Gregory Cauchie" initials="G." surname="Cauchie">
<organization>KOEVOO</organization>
<address>
<postal>
<country>France</country>
</postal>
<email>gregory@koevoo.tech</email>
</address>
</author>
<section anchor="overview" title="Overview"> <date month="October" year="2022"/>
<area>rtg</area>
<workgroup>bier</workgroup>
<t> BIER-TE is based on the (non-TE) BIER architecture, terminology and packet f <keyword>BIER</keyword>
ormats as described <keyword>BIER-TE</keyword>
in <xref target="RFC8279"/> and <xref target="RFC8296"/>. <keyword>controller</keyword>
This document describes BIER-TE in the expectation that the reader is familiar <keyword>ECMP</keyword>
with these two documents.</t> <keyword>forwarding</keyword>
<keyword>traffic-engineering</keyword>
<keyword>multicast</keyword>
<keyword>pseudocode</keyword>
<keyword>routing</keyword>
<keyword>traffic-steering</keyword>
<keyword>tree-steering</keyword>
<t>BIER-TE introduces a new semantic for "bit positions" (BP). They indicate adj <abstract>
acencies <t> This memo describes per-packet stateless strict and loose path
steered replication and forwarding for "Bit Index Explicit Replication" (BIER)
packets (RFC 8279); it is called "Tree Engineering for Bit Index Explicit Replic
ation" (BIER-TE) and is intended to be used as the path steering mechanism for T
raffic Engineering
with BIER.</t>
<t>BIER-TE introduces a new semantic for "bit positions" (BPs). These BPs
indicate adjacencies
of the network topology, as opposed to (non-TE) BIER in which BPs indicate of the network topology, as opposed to (non-TE) BIER in which BPs indicate
"Bit-Forwarding Egress Routers" (BFER). A BIER-TE packets BitString therefore "Bit-Forwarding Egress Routers" (BFERs). A BIER-TE "packets BitString" therefo
indicates the re indicates the
edges of the (loop-free) tree that the packet is forwarded across by BIER-TE. edges of the (loop-free) tree across which the packets are forwarded by BIER-TE.
With BIER-TE, the "Bit Index Forwarding Table" (BIFT) of each "Bit Forwarding Ro BIER-TE can leverage BIER forwarding engines with little changes.
uter" (BFR) Co-existence of BIER and BIER-TE forwarding in the same domain is possible -- fo
is only populated with BP that are adjacent to the BFR r example, by using
in the BIER-TE Topology. Other BPs are empty in the BIFT. The BFR replicate separate BIER "subdomains" (SDs). Except for the optional routed adjacencies, BI
and forwards BIER packets to adjacent BPs that are set in the packet. ER-TE does not
require a BIER routing underlay and can therefore operate without depending
on a routing protocol such as the "Interior Gateway Protocol" (IGP).</t>
</abstract>
</front>
<middle>
<section anchor="overview" numbered="true" toc="default">
<name>Overview</name>
<t>"Tree Engineering for Bit Index Explicit Replication" (BIER-TE) is base
d on the (non-TE) BIER architecture, terminology, and packet formats as describe
d
in <xref target="RFC8279" format="default"/> and <xref target="RFC8296" format="
default"/>.
This document describes BIER-TE, with the expectation that the reader is familia
r
with these two documents.</t>
<t>BIER-TE introduces a new semantic for "bit positions" (BPs). These BPs
indicate adjacencies
of the network topology, as opposed to (non-TE) BIER in which BPs indicate
"Bit-Forwarding Egress Routers" (BFERs). A BIER-TE "packets BitString" therefo
re indicates the
edges of the (loop-free) tree across which the packets are forwarded by BIER-TE.
With BIER-TE, the "Bit Index Forwarding Table" (BIFT) of each "Bit-Forwarding Ro
uter" (BFR)
is only populated with BPs that are adjacent to the BFR
in the BIER-TE topology. Other BPs are empty in the BIFT. The BFR replicates
and forwards BIER packets to adjacent BPs that are set in the packets.
BPs are normally also cleared upon forwarding to avoid duplicates and loops. BPs are normally also cleared upon forwarding to avoid duplicates and loops.
</t> </t>
<t>BIER-TE can leverage BIER forwarding engines with little or no changes.
<t>BIER-TE can leverage BIER forwarding engines with little or no changes. It can also co-exist with BIER forwarding in the same domain -- for example, by
It can also co-exist with BIER forwarding in the same domain, for example by usi using
ng separate BIER subdomains. Except for the optional routed adjacencies, BIER-TE do
separate BIER sub-domains. Except for the optional routed adjacencies, BIER-TE d es not
oes not require a BIER routing underlay and can therefore operate without depending
require a BIER routing underlay, and can therefore operate without depending on a routing protocol such as the "Interior Gateway Protocol" (IGP).</t>
on an "Interior Gateway Routing protocol" (IGP).</t> <t>This document is structured as follows:
</t>
<t>This document is structured as follows: <ul spacing="normal">
<list style="symbols"> <li>
<t><xref target="introduction"/> introduces BIER-TE with two <xref target="introduction" format="default"/> introduces BIER-TE with
forwarding examples, followed by an introduction of the new concepts of the two
BIER-TE forwarding examples, followed by an introduction to the new concepts of the
(overlay) topology and finally a summary of the relationship between BIER an BIER-TE
d BIER-TE and a discussion of accelerated hardware forwarding.</t> (overlay) topology, and finally a summary of the relationship between BIER a
<t><xref target="components"/> describes the components of the BIER-TE archi nd BIER-TE and a discussion of accelerated hardware forwarding.</li>
tecture, <li>
Flow overlay, BIER-TE layer with the BIER-TE control plane (including the B <xref target="components" format="default"/> describes the components
IER-TE controller) and BIER-TE forwarding plane, and the routing underlay.</t> of the BIER-TE architecture: the multicast
<t><xref target="forwarding"/> specifies the behavior of the BIER-TE forward flow overlay, the BIER-TE layer with the BIER-TE control plane (including t
ing plane with the different type of adjacencies and possible variations of BIER he BIER-TE controller), the BIER-TE forwarding plane, and the routing underlay.<
-TE forwarding pseudocode, and finally the mandatory and optional requirements.< /li>
/t> <li>
<t><xref target="controller-ops"/> describes operational considerations for <xref target="forwarding" format="default"/> specifies the behavior of
the BIER-TE controller, foremost how the BIER-TE controller can optimize the use the BIER-TE forwarding plane with the different types of adjacencies and possib
of BP by using specific type of BIER-TE adjacencies for different type of topol le variations of BIER-TE forwarding pseudocode, and finally the mandatory and op
ogical situations, but also how to assign bits to avoid loops and duplicates (wh tional requirements.</li>
ich in BIER-TE does not come for free), and finally how "Set Identifier" (SI), " <li>
sub-domain" (SD) and BFR-ids can be managed by a BIER-TE controller, examples an <xref target="controller-ops" format="default"/> describes operational
d summary.</t> considerations for the BIER-TE controller, primarily how the BIER-TE controller
<t><xref target="SR"/> concludes the technology specific sections of the doc can optimize the use of BPs by using specific types of BIER-TE adjacencies for
ument by further relating BIER-TE to Segment Routing (SR).</t> different types of topological situations. It also describes how to assign bits
</list></t> to avoid loops and duplicates (which, in BIER-TE, does not come "for free"). F
inally, it discusses how "Set Identifiers" (SIs), "subdomains" (SDs), and BFR-id
<t>Note that related work, <xref target="I-D.ietf-roll-ccast"/> s can be managed by a BIER-TE controller; examples and a summary are provided.</
uses Bloom filters <xref target="Bloom70"/> to represent leaves or edges of the li>
intended delivery tree. Bloom filters <li>
<xref target="SR" format="default"/> concludes this document; details
regarding the relationship between BIER-TE and "Segment Routing" (SR) are discus
sed.</li>
</ul>
<t>Note that related work <xref target="I-D.ietf-roll-ccast" format="defau
lt"/>
uses Bloom filters <xref target="Bloom70" format="default"/> to represent leaves
or edges of the intended delivery tree. Bloom filters
in general can support larger trees/topologies with fewer addressing bits than e xplicit BitStrings, in general can support larger trees/topologies with fewer addressing bits than e xplicit BitStrings,
but they introduce the heuristic risk of false positives and cannot clear bits i n but they introduce the heuristic risk of false positives and cannot clear bits i n
the BitString during forwarding to avoid loops. For these reasons, BIER-TE the BitStrings during forwarding to avoid loops. For these reasons, BIER-TE, lik
uses explicit BitStrings like BIER. The explicit BitStrings of BIER-TE can also e BIER,
be seen as a special type of Bloom filter, and this is how related work <xref ta uses explicit BitStrings. Explicit BitStrings as used by BIER-TE can also
rget="ICC"/> be seen as a special type of Bloom filter, and this is how other related work <x
ref target="ICC" format="default"/>
describes it.</t> describes it.</t>
<!-- Removed for now by review with Lou Berger
<section anchor="te" title="BIER-TE and Traffic Engineering (BIER-TE)">
<t>BIER-TE is not a standalone, complete traffic engineering signaling solution
such as RSVP with RSVP-TE
extensions (<xref target="RFC2205"/>, <xref target="RFC3209"/>). Instead it is a
(non-TE) BIER derived architecture
and forwarding plane that allows to signal "source-routed" paths and replication
points without
per-path, per-replication-point state on the transit nodes. This document introd
uces the name
"Tree Engineering" for BitStrings using this semantic. BIER-TE is therefore more
similar to Segment Routing
(SR, (<xref target="RFC8402"/>)) than RSVP-TE. Note that SR does not provide sta
teless replication point
and receiver set signaling in its packet header. See <xref target="SR"/> for a
more detailed discussion of
BIER-TE and SR.</t>
<t>BIER-TE can be used alone in use cases not requiring bandwidth or buffer reso
urce reservations,
such as high resilient services through dual transmission with path diversity or
optimization
of network capacity utilization through calculated paths/trees ("load balancing
across non-ECMP paths").
Due to its stateless BIER approach, BIER-TE does not create per-flow/per-tree st
ate on intermedia nodes.</t>
<t>BIER-TE can also be combined with bandwidth and buffer management functions t
o support
traffic engineering such as per-flow guaranteed bandwidth and guaranteed latency
across BIER-TE
steered paths / trees. Combinations of BIER or BIER-TE with such per-tree/per-fl
ow resource
guarantees are called BIER-TE. The following paragraphs summarize options and c
onsiderations.</t>
<t>In <xref target="components"/> below, the BIER-TE architecture specifies the
BIER-TE Controller
as an entity calculating both the BIER-TE topology and desired paths/trees for o
verlay flows
based on the desired policies. A Path Computation Engine (PCE, see <xref target=
"RFC4655"/>)
that can calculate the BitString for BIER-TE is an instance of such a BIER-TE Co
ntroller.
If the PCE can also perform resource management such as per-flow bandwidth reser
vations and
optional latency guarantees, then it becomes a PCE for BIER-TE with traffic eng
ineering.</t>
<t>To support bandwidth guarantees in the forwarding plane, the ingres BIER-TE n
ode
(BFIR) may need to have a per-flow policer if ingressed traffic is not trusted t
o stay within
its admitted traffic envelope. This is a well understood policy function that ca
n be deployed
without changes to BIER-TE.</t>
<t>If latency guarantees as required as for example by Guaranteed Services (<xre
f target="RFC2212"/>),
then additional per-hop latency control in the forwarding plane can be required.
This can also
be added to BIER-TE deployments without changes to BIER-TE. Per-hop stateless so
lutions for this
such as in <xref target="I-D.qiang-detnet-large-scale-detnet"/> would allow to m
aintain
the per-hop stateless design goal of BIER-TE and expand it into BIER-TE. Per-hop
stateful solutions like
per-flow, per-hop shaping may also be beneficial given how BIER-TE eliminates th
e need for
per-flow, per-hop multicast replication and steering state.</t>
<t>Mechanisms how to combine BIER-TE or BIER with other mechanisms to build BIER
-TE are outside
the scope of this document. See <xref target="I-D.eckert-teas-bier-te-framework
"/>.</t>
</section>
<section anchor="boilerplate" title="Requirements Language">
<t>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL
"
in this document are to be interpreted as described in BCP 14 <xref target="RFC
2119"/>
<xref target="RFC8174"/> when, and only when, they appear in all capitals, as s
hown here.
</t>
</section> </section>
</section> <section anchor="introduction" numbered="true" toc="default">
<name>Introduction</name>
<section anchor="introduction" title="Introduction"> <section anchor="boilerplate" numbered="true" toc="default">
<name>Requirements Language</name>
<section anchor="examples" title="Basic Examples"> <t>The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
"<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>",
<t>BIER-TE forwarding is best introduced with simple examples. These examples "<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOULD</bcp14>",
use formal terms defined later in the document (<xref target="adjacencies"/>), "<bcp14>SHOULD NOT</bcp14>",
including forward_connected(), forward_routed() and local_decap(). "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
"<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document
are to be interpreted as described in BCP&nbsp;14
<xref target="RFC2119"/> <xref target="RFC8174"/> when, and only
when, they appear in all capitals, as shown here.</t>
</section>
<section anchor="examples" numbered="true" toc="default">
<name>Basic Examples</name>
<t>BIER-TE forwarding is best introduced with simple examples. These exa
mples
use formal terms defined later in this document (<xref target="adjacencies" form
at="default"/> in <xref target="btft"/>),
including forward_connected(), forward_routed(), and local_decap().
</t> </t>
<t>Consider the simple network in the BIER-TE overview example shown in
<figure anchor="basic-example" title="BIER-TE basic example"> <xref target="basic-example"/>, with six BFRs. &nbsp;p1...p15 are the bit positi
<artwork align="left"><![CDATA[ ons used. All BFRs can act as
a "Bit-Forwarding Ingress Router" (BFIR); BFR1, BFR3, BFR4, and
BFR6 can also be BFERs. "Forward_connected()" is the name used for
adjacencies that represent subnet adjacencies of the network.
"Local_decap()" is the name used for the adjacency that decapsulates BIER-TE pac
kets and
passes their payload to higher-layer processing.
</t>
<figure anchor="basic-example">
<name>BIER-TE Basic Example</name>
<artwork align="left" name="" type="" alt=""><![CDATA[
BIER-TE Topology: BIER-TE Topology:
Diagram: Diagram:
p5 p6 p5 p6
--- BFR3 --- --- BFR3 ---
p3/ p13 \p7 p15 p3/ p13 \p7 p15
BFR1 ---- BFR2 BFR5 ----- BFR6 BFR1 ---- BFR2 BFR5 ----- BFR6
p1 p2 p4\ p14 /p10 p11 p12 p1 p2 p4\ p14 /p10 p11 p12
--- BFR4 --- --- BFR4 ---
p8 p9 p8 p9
(simplified) BIER-TE Bit Index Forwarding Tables (BIFT): (simplified) BIER-TE Bit Index Forwarding Tables (BIFTs):
BFR1: p1 -> local_decap() BFR1: p1 -> local_decap()
p2 -> forward_connected() to BFR2 p2 -> forward_connected() to BFR2
BFR2: p1 -> forward_connected() to BFR1 BFR2: p1 -> forward_connected() to BFR1
p5 -> forward_connected() to BFR3 p5 -> forward_connected() to BFR3
p8 -> forward_connected() to BFR4 p8 -> forward_connected() to BFR4
BFR3: p3 -> forward_connected() to BFR2 BFR3: p3 -> forward_connected() to BFR2
p7 -> forward_connected() to BFR5 p7 -> forward_connected() to BFR5
skipping to change at line 264 skipping to change at line 193
BFR4: p4 -> forward_connected() to BFR2 BFR4: p4 -> forward_connected() to BFR2
p10 -> forward_connected() to BFR5 p10 -> forward_connected() to BFR5
p14 -> local_decap() p14 -> local_decap()
BFR5: p6 -> forward_connected() to BFR3 BFR5: p6 -> forward_connected() to BFR3
p9 -> forward_connected() to BFR4 p9 -> forward_connected() to BFR4
p12 -> forward_connected() to BFR6 p12 -> forward_connected() to BFR6
BFR6: p11 -> forward_connected() to BFR5 BFR6: p11 -> forward_connected() to BFR5
p15 -> local_decap() p15 -> local_decap()
]]></artwork>
]]></artwork></figure> </figure>
<t>
<t> Assume that a packet from BFR1 should be sent via BFR4 to BFR6. This requires
Consider the simple network in the above BIER-TE overview example picture
with 6 BFRs. p1...p15 are the bit positions used. All BFRs can act as
an ingress BFR (BFIR), BFR1, BFR3, BFR4 and
BFR6 can also be BFERs. Forward_connected() is the name for
adjacencies that are representing subnet adjacencies of the network.
Local_decap() is the name of the adjacency to decapsulate BIER-TE packets and
pass their payload to higher layer processing.
</t>
<t>
Assume a packet from BFR1 should be sent via BFR4 to BFR6. This requires
a BitString (p2,p8,p10,p12,p15). When this packet is examined by BIER-TE a BitString (p2,p8,p10,p12,p15). When this packet is examined by BIER-TE
on BFR1, the only bit position from the BitString that is also set in on BFR1, the only bit position from the BitString that is also set in
the BIFT is p2. This will cause BFR1 to send the only copy of the packet the BIFT is p2. This will cause BFR1 to send the only copy of the packet
to BFR2. Similarly, BFR2 will forward to BFR4 because of p8, BFR4 to BFR5 to BFR2. Similarly, BFR2 will forward to BFR4 because of p8, BFR4 to BFR5
because of p10 and BFR5 to BFR6 because of p12. p15 finally makes BFR6 receive because of p10, and BFR5 to BFR6 because of p12. &nbsp;p15 finally makes BFR6 re ceive
and decapsulate the packet. and decapsulate the packet.
</t> </t>
<t>To send a copy to BFR6 via BFR4 and also a copy to BFR3, the BitStrin
<t>To send a copy to BFR6 via BFR4 and also a copy to BFR3, the BitString needs g needs
to be (p2,p5,p8,p10,p12,p13,p15). When this packet is examined by to be (p2,p5,p8,p10,p12,p13,p15). When this packet is examined by
BFR2, p5 causes one copy to be sent to BFR3 and p8 one copy to BFR4. BFR2, p5 causes one copy to be sent to BFR3 and p8 one copy to BFR4.
When BFR3 receives the packet, p13 will cause it to receive and decapsulate When BFR3 receives the packet, p13 will cause it to receive and decapsulate
the packet. the packet.
</t> </t>
<t>If instead the BitString was (p2,p6,p8,p10,p12,p13,p15), the packet
<t>If instead the BitString was (p2,p6,p8,p10,p12,p13,p15), the packet
would be copied by BFR5 towards BFR3 because of p6 instead of being copied by would be copied by BFR5 towards BFR3 because of p6 instead of being copied by
BFR2 to BFR3 because of p5 in the prior case. This is showing the ability of the BFR2 to BFR3 because of p5 in the prior case. This demonstrates the ability of t
shown he
BIER-TE Topology to make the traffic pass across any possible path and be BIER-TE topology, as shown in <xref target="basic-example"/>, to make the traffi
c pass across any possible path and be
replicated where desired. replicated where desired.
</t> </t>
<t>BIER-TE has various options for minimizing BP assignments,
<t>BIER-TE has various options to minimize BP assignments,
many of which are based on out-of-band knowledge about the required multicast tr affic many of which are based on out-of-band knowledge about the required multicast tr affic
paths and bandwidth consumption in the network, such as from pre-deployment plan paths and bandwidth consumption in the network, e.g., from predeployment plannin
ning.</t> g.</t>
<t><xref target="basic-overlay" format="default"/> shows a modified exam
<t><xref target="basic-overlay"/> shows a modified example, in which Rtr2 and Rt ple, in which Rtr2 and Rtr5 are
r5 are
assumed not to support BIER-TE, so traffic has to be unicast encapsulated across assumed not to support BIER-TE, so traffic has to be unicast encapsulated across
them. To emphasize non-L2, but routed/tunneled forwarding of BIER-TE packets, them. To explicitly distinguish routed/tunneled forwarding of BIER-TE packets
these adjacencies are called "forward_routed". Otherwise, there is no difference from Layer 2 forwarding (forward_connected()), these adjacencies are called "for
ward_routed()" adjacencies. Otherwise, there is no difference
in their processing over the aforementioned forward_connected() adjacencies.</t> in their processing over the aforementioned forward_connected() adjacencies.</t>
<t>In addition, bits are saved in the following example by assuming that
<t>In addition, bits are saved in the following example by assuming that BFR1 on BFR1 only
ly needs to be a BFIR -- not a BFER or a transit BFR.</t>
needs to be BFIR but not BFER or transit BFR.</t> <figure anchor="basic-overlay">
<name>BIER-TE Basic Overlay Example</name>
<figure anchor="basic-overlay" title="BIER-TE basic overlay example"> <artwork align="left" name="" type="" alt=""><![CDATA[
<artwork align="left"><![CDATA[
BIER-TE Topology: BIER-TE Topology:
Diagram: Diagram:
p1 p3 p7 p1 p3 p7
....> BFR3 <.... p5 ....> BFR3 <.... p5
........ ........> ........ ........>
BFR1 (Rtr2) (Rtr5) BFR6 BFR1 (Rtr2) (Rtr5) BFR6
........ ........> p9 ........ ........> p9
....> BFR4 <.... p6 ....> BFR4 <.... p6
p2 p4 p8 p2 p4 p8
(simplified) BIER-TE Bit Index Forwarding Tables (BIFT): (simplified) BIER-TE Bit Index Forwarding Tables (BIFTs):
BFR1: p1 -> forward_routed() to BFR3 BFR1: p1 -> forward_routed() to BFR3
p2 -> forward_routed() to BFR4 p2 -> forward_routed() to BFR4
BFR3: p3 -> local_decap() BFR3: p3 -> local_decap()
p5 -> forward_routed() to BFR6 p5 -> forward_routed() to BFR6
BFR4: p4 -> local_decap() BFR4: p4 -> local_decap()
p6 -> forward_routed() to BFR6 p6 -> forward_routed() to BFR6
BFR6: p7 -> forward_routed() to BFR3 BFR6: p7 -> forward_routed() to BFR3
p8 -> forward_routed() to BFR4 p8 -> forward_routed() to BFR4
p9 -> local_decap() p9 -> local_decap()
]]></artwork>
]]></artwork></figure> </figure>
<t>To send a BIER-TE packet from BFR1 via BFR3 to be received by BFR6,
<t>To send a BIER-TE packet from BFR1 via BFR3 to be received by BFR6, the BitString is (p1,p5,p9). A packet from BFR1 via BFR4 to be received by BFR6
the BitString is (p1,p5,p9). From BFR1 via BFR4 to be received by BFR6, uses the BitString (p2,p6,p9). A packet from BFR1 to be received by BFR3,BFR4
the BitString is (p2,p6,p9). A packet from BFR1 to be received by BFR3,BFR4
and from BFR3 to be received by BFR6 uses (p1,p2,p3,p4,p5,p9). A packet and from BFR3 to be received by BFR6 uses (p1,p2,p3,p4,p5,p9). A packet
from BFR1 to be received by BFR3,BFR4 and from BFR4 to be received by BFR6 from BFR1 to be received by BFR3,BFR4 and from BFR4 to be received by BFR6
uses (p1,p2,p3,p4,p6,p9). A packet from BFR1 to be received by BFR4, uses (p1,p2,p3,p4,p6,p9). A
and from BFR4 to be received by BFR6 and from there to be received by BFR3 uses packet from BFR1 to be received by BFR4, then from BFR4 to be
(p2,p3,p4,p6,p7,p9). received by BFR6, and finally from BFR6 to be received by BFR3, uses
A packet from BFR1 to be received by BFR3, and from BFR3 to be received by BFR6 (p2,p3,p4,p6,p7,p9). A packet from BFR1 to be received by BFR3,
there to be received by BFR4 uses (p1,p3,p4,p5,p8,p9).</t> then from BFR3 to be received by BFR6, and finally from BFR6 to be
received by BFR4, uses (p1,p3,p4,p5,p8,p9).
</section>
<section anchor="topology" title="BIER-TE Topology and adjacencies">
<t>The key new component in BIER-TE compared to (non-TE) BIER is the BIER-TE top
ology
as introduced through the two examples in <xref target="examples"/>.
It is used to control where replication can or should happen and how to
minimize the required number of BP for adjacencies.
</t> </t>
</section>
<t> <section anchor="topology" numbered="true" toc="default">
The BIER-TE Topology consists of the BIFTs of all the BFR and <name>BIER-TE Topology and Adjacencies</name>
<t>The key new component in BIER-TE compared to (non-TE) BIER is the BIE
R-TE topology
as introduced through the two examples in <xref target="examples" format="defaul
t"/>.
It is used to control where replication can or should happen and how to
minimize the required number of BPs for adjacencies.
</t>
<t>
The BIER-TE topology consists of the BIFTs of all the BFRs and
can also be expressed as a directed graph where the edges are the adjacencies can also be expressed as a directed graph where the edges are the adjacencies
between the BFRs labelled with the BP used for the adjacency. Adjacencies are between the BFRs labeled with the BP used for the adjacency. Adjacencies are
naturally unidirectional. BP can be reused across multiple adjacencies as long naturally unidirectional. A BP can be reused across multiple adjacencies as lon
as this does not g as this does not
lead to undesired duplicates or loops as explained in <xref target="avoiding"/>. lead to undesired duplicates or loops, as explained in <xref target="avoiding" f
ormat="default"/>.
</t> </t>
<t>If the BIER-TE topology represents (a subset of) the underlying (Laye
<t>If the BIER-TE topology represents (a subset of) the underlying (layer 2) r 2)
topology of the network as shown in the first example, this may be called a "nat topology of the network as shown in the first example, this may be called an "un
ive" derlay"
BIER-TE topology. A topology consisting only of "forward_routed" adjacencies as BIER-TE topology. A topology consisting only of "forward_routed()" adjacencies a
s
shown in the second example may be called an "overlay" BIER-TE topology. shown in the second example may be called an "overlay" BIER-TE topology.
A BIER-TE topology with both forward_connected() and forward_routed() adjacencie s A BIER-TE topology with both forward_connected() and forward_routed() adjacencie s
may be called a "hybrid" BIER-TE topology.</t> may be called a "hybrid" BIER-TE topology.</t>
</section>
</section> <section anchor="comparison" numbered="true" toc="default">
<!-- topology --> <name>Relationship to BIER</name>
<t>BIER-TE is designed so that its forwarding plane is a simple extensio
<section anchor="comparison" title="Relationship to BIER"> n to the (non-TE) BIER forwarding plane, hence allowing it to be added to BIER d
eployments where it can be beneficial.</t>
<t>BIER-TE is designed so that its forwarding plane is a simple extension to the <t>BIER-TE is also intended as an option to expand the BIER architecture
(non-TE) BIER forwarding plane, hence allowing for it to be added to BIER deplo into deployments where (non-TE) BIER may not be the best fit, such as statical
yments where it can be beneficial.</t> ly provisioned networks that need path steering but do not want distributed rout
<t>BIER-TE is also intended as an option to expand the BIER architecture into de ing protocols.</t>
ployments where (non-TE) BIER may not be the best fit, such as statically provi <ol spacing="normal" type="1"><li>
sioned networks with needs for path steering but without desire for distributed <t>BIER-TE inherits the following aspects from BIER unchanged:
routing protocols.</t> </t>
<ol spacing="normal" type="%p%c"><li>The fundamental purpose of per-
<t><list style="numbers"> packet signaled replication and delivery via a BitString.</li>
<t>BIER-TE inherits the following aspects from BIER unchanged: <li>The overall architecture, which consists of three layers: the
<list style="numbers"> flow overlay, the BIER(-TE) layer, and the routing underlay.</li>
<t>The fundamental purpose of per-packet signaled replication and delivery v <li>The supported encapsulations <xref target="RFC8296" format="de
ia a BitString.</t> fault"/>.</li>
<t>The overall architecture consisting of three layers, flow overlay, BIER(- <li>The semantics of all BIER header elements <xref target="RFC829
TE) layer and routing underlay.</t> 6" format="default"/> used by the BIER-TE forwarding plane, other than the seman
<t>The supported encapsulations <xref target="RFC8296"/>.</t> tic of the BP in the BitString.</li>
<t>The semantic of all <xref target="RFC8296"/> header elements used by the <li>The BIER forwarding plane, except for how bits have to be clea
BIER-TE forwarding plane other than the semantic of the BP in the BitString.</t> red during replication.</li>
<t>The BIER forwarding plane, except for how bits have to be cleared during </ol>
replication.</t> </li>
</list></t> <li>
<t>BIER-TE has the following key changes with respect to BIER:
<t>BIER-TE has the following key changes with respect to BIER: </t>
<list style="numbers"> <ol spacing="normal" type="%p%c"><li>In BIER, bits in the BitString
<t>In BIER, bits in the BitString of a BIER packet header indicate a BFER of a BIER packet header indicate a BFER,
and bits in the BIFT indicate the BIER control plane calculated next-hop and bits in the BIFT indicate the BIER control plane's calculated next h
toward that BFER. In BIER-TE, a bit in the BitString of a BIER packet op
towards that BFER. In BIER-TE, a bit in the BitString of a BIER packet
header indicates an adjacency in the BIER-TE topology, and only the header indicates an adjacency in the BIER-TE topology, and only the
BFR that is the upstream of that adjacency has its BP populated with BFR that is the upstream of that adjacency has its BP populated with
the adjacency in its BIFT.</t> the adjacency in its BIFT.</li>
<li>In BIER, the implied reference options for the core part of th
<t>In BIER, the implied reference options for the core part of the BIER laye e
r BIER layer
control plane are the BIER extensions for distributed routing protocols. control plane are the BIER extensions for distributed routing protocols.
This includes ISIS/OSPF extensions for BIER, <xref target="RFC8401"/> These include IS-IS and OSPF extensions for BIER, as specified in <xref t
and <xref target="RFC8444"/>.</t> arget="RFC8401" format="default"/>
and <xref target="RFC8444" format="default"/>, respectively.</li>
<t>The reference option for the core part of the BIER-TE control plane is <li>The reference option for the core part of the BIER-TE control
the BIER-TE controller. Nevertheless, both the BIER and BIER-TE BIFTs for plane is
warding the BIER-TE controller. Nevertheless, both the BIER and BIER-TE BIFTs' fo
plane state could equally be populated by any mechanism.</t> rwarding
<t>Assuming the reference options for the control plane, BIER-TE replaces i plane state could equally be populated by any mechanism.</li>
n-network autonomous path calculation by explicit paths calculated by the BIER-T <li>Assuming the reference options for the control plane, BIER-TE
E controller.</t> replaces in-network autonomous path calculations with explicit paths calculated
</list></t> by the BIER-TE controller.</li>
</ol>
<t>The following elements/functions described in the BIER architecture are not r </li>
equired by the BIER-TE architecture: <li>
<list style="numbers"> <t>The following elements/functions described in the BIER architectu
<t>"Bit Index Routing Tables" (BIRTs) are not required on BFRs for BIER-TE w re are not required by the BIER-TE architecture:
hen using a BIER-TE controller because the controller can directly populate the </t>
BIFTs. In BIER, BIRTs are populated by the distributed routing protocol support <ol spacing="normal" type="%p%c"><li>"Bit Index Routing Tables" (BIR
for BIER, allowing BFRs to populate their BIFTs locally from their BIRTs. Other Ts) are not required on BFRs for BIER-TE when using a BIER-TE controller, becaus
BIER-TE control plane or management plane options may introduce requirements fo e the controller can directly populate the BIFTs. In BIER, BIRTs are populated b
r BIRTs for BIER-TE BFRs.</t> y the distributed routing protocol support for BIER, allowing BFRs to populate t
<t>The BIER-TE layer forwarding plane does not require BFRs to have a unique heir BIFTs locally from their BIRTs. Other BIER-TE control plane or management
BP and therefore also no unique BFR-id. See <xref target="leaf-bfer"/>.</t> plane options may introduce requirements for BIRTs for BIER-TE BFRs.</li>
<t>Identification of BFRs by the BIER-TE control plane is outside the scope <li>The BIER-TE layer forwarding plane does not require BFRs to ha
of this specification. Whereas the BIER control plane uses BFR-ids in its BFR to ve a unique BP; see <xref target="leaf-bfer" format="default"/>. Therefore, BFRs
BFR signaling, a BIER-TE controller may choose any form of identification deeme may not have a unique BFR-id; see <xref target="bfr-id"/>.</li>
d appropriate.</t> <li>Identification of BFRs by the BIER-TE control plane is outside
<t>BIER-TE forwarding does not require the BFIR-id field of the BIER packet the scope of this specification. Whereas the BIER control plane uses BFR-ids in
header.</t> its BFR-to-BFR signaling, a BIER-TE controller may choose any form of identific
</list></t> ation deemed appropriate.</li>
<li>BIER-TE forwarding does not require the BFIR-id field of the B
<t>Co-existence of BIER and BIER-TE in the same network requires the following: IER packet header.</li>
<list style="numbers"> </ol>
<t>The BIER/BIER-TE packet header needs to allow addressing both BIER and BIER-T </li>
E BIFTs. Depending on the encapsulation option, the same SD may or may not be re <li>
usable across BIER and BIER-TE. See <xref target="encapsulation"/>. <t>Co-existence of BIER and BIER-TE in the same network requires the
In either case, a packet is always only forwarded end-to-end via BIER or via BIE following:
R-TE (ships in the nights forwarding).</t> </t>
<ol spacing="normal" type="%p%c"><li>The BIER/BIER-TE packet header
<t>BIER-TE deployments will have to assign BFR-ids to BFRs and insert them into needs to allow the addressing of both BIER and BIER-TE BIFTs. Depending on the e
the BFIR-id field of BIER packet headers as BIER does, whenever the deployment u ncapsulation option, the same SD may or may not be reusable across BIER and BIER
ses (unchanged) components developed for BIER that use BFR-id, such as multicast -TE. See <xref target="encapsulation" format="default"/>.
flow overlays or BIER layer control plane elements. See also <xref target="bfr- In either case, a packet is always forwarded only end to end via BIER or via BIE
id"/>.</t> R-TE ("ships in the night" forwarding).</li>
<li>BIER-TE deployments will have to assign BFR-ids to BFRs and in
</list></t> sert them into the BFIR-id field of BIER packet headers, as does BIER, whenever
the deployment uses (unchanged) components developed for BIER that use BFR-ids,
</list></t> such as multicast flow overlays or BIER layer control plane elements. See also <
xref target="bfr-id" format="default"/>.</li>
</section> </ol>
</li>
<section anchor="fwd-comparison" title="Accelerated/Hardware forwarding comp </ol>
arison"> </section>
<section anchor="fwd-comparison" numbered="true" toc="default">
<t>BIER-TE forwarding rules, especially the BitString parsing are designed to be <name>Accelerated Hardware Forwarding Comparison</name>
as close <t>BIER-TE forwarding rules, especially BitString parsing, are designed
as possible to those of BIER in the expectation that this eases the programming to be as close
of BIER-TE forwarding as possible to those of BIER, with the expectation that this eases the programmi
ng of BIER-TE forwarding
code and/or BIER-TE forwarding hardware on platforms supporting BIER. code and/or BIER-TE forwarding hardware on platforms supporting BIER.
The pseudocode in <xref target="pseudocode"/> shows how existing The pseudocode in <xref target="pseudocode" format="default"/> shows how existin g
(non-TE) BIER/BIFT forwarding can be modified to support the required BIER-TE fo rwarding (non-TE) BIER/BIFT forwarding can be modified to support the required BIER-TE fo rwarding
functionality (<xref target="requirements"/>), by using BIER BIFT's "Forwarding functionality (<xref target="requirements" format="default"/>), by using the BIE
Bit Mask" (F-BM): R BIFT's "Forwarding Bit Mask" (F-BM):
Only the clearing of bits to avoid duplicate only the clearing of bits to avoid sending duplicate
packets to a BFR's neighbor is skipped in BIER-TE forwarding because it is not n packets to a BFR's neighbor is skipped in BIER-TE forwarding, because it is not
ecessary necessary
and could not be done when using BIER F-BM.</t> and could not be done when using a BIER F-BM.</t>
<t>Whether to use BIER or BIER-TE forwarding is simply a choice of the m
<t>Whether to use BIER or BIER-TE forwarding is simply a choice of the mode ode
of the BIFT indicated by the packet (BIER or BIER-TE BIFT). This is determined of the BIFT indicated by the packet (BIER or BIER-TE BIFT). This is determined
by the BFR configuration for the encapsulation, see <xref target="encapsulation" by the BFR configuration for the encapsulation; see <xref target="encapsulation"
/>.</t> format="default"/>.</t>
</section>
</section>
<!-- fwd-comparison -->
</section> </section>
<!-- overview -->
<section anchor="components" title="Components"> <section anchor="components" numbered="true" toc="default">
<name>Components</name>
<t>BIER-TE can be thought of being constituted from the same three <t>BIER-TE can be thought of as being composed of the same three
layers as BIER: The "multicast flow overlay", the "BIER layer" and layers as BIER: the "multicast flow overlay", the "BIER layer", and
the "routing underlay". The following picture also shows how the "BIER layer" the "routing underlay". <xref target="architecture"/> also shows how the BIER l
is constituted from the "BIER-TE forwarding plane" and the "BIER-TE control plan ayer
e" is composed of the "BIER-TE forwarding plane" and the "BIER-TE control plane" as
represent by the "BIER-TE Controller".</t> represented by the "BIER-TE controller".
</t>
<figure anchor="architecture" title="BIER-TE architecture"> <figure anchor="architecture">
<artwork align="left"><![CDATA[ <name>BIER-TE Architecture</name>
<artwork align="left" name="" type="" alt=""><![CDATA[
<------BGP/PIM-----> <------BGP/PIM----->
|<-IGMP/PIM-> multicast flow <-PIM/IGMP->| |<-IGMP/PIM-> multicast flow <-PIM/IGMP->|
overlay overlay
BIER-TE [BIER-TE Controller] <=> [BIER-TE Topology] BIER-TE [BIER-TE Controller] <=> [BIER-TE Topology]
control ^ ^ ^ control ^ ^ ^
plane / | \ BIER-TE control protocol plane / | \ BIER-TE control protocol
| | | e.g. YANG/NETCONF/RESTCONF | | | (e.g., YANG/NETCONF/RESTCONF
| | | PCEP/... | | | PCEP/...)
v v v v v v
Src -> Rtr1 -> BFIR-----BFR-----BFER -> Rtr2 -> Rcvr Src -> Rtr1 -> BFIR-----BFR-----BFER -> Rtr2 -> Rcvr
|<----------------->| |<----------------->|
BIER-TE forwarding plane BIER-TE forwarding plane
|<- BIER-TE domain->| |<- BIER-TE domain->|
|<--------------------->| |<--------------------->|
Routing underlay Routing underlay
]]></artwork></figure> ]]></artwork>
</figure>
<section anchor="flow-overlay" title="The Multicast Flow Overlay"> <section anchor="flow-overlay" numbered="true" toc="default">
<name>The Multicast Flow Overlay</name>
<t>The Multicast Flow Overlay has the same role as described for BIER <t>The multicast flow overlay has the same role as that described for BI
in <xref target="RFC8279"/>, Section 4.3. See also <xref target="engineered-bits ER
trings"/>.</t> in <xref target="RFC8279" sectionFormat="comma" section="4.3"/>. See also <xref
target="engineered-bitstrings" format="default"/>.</t>
<t>When a BIER-TE controller is used, then the signaling for the Multicast Flow <t>When a BIER-TE controller is used, it might also be preferable that
Overlay may multicast flow overlay signaling be performed through a central point of control
also be preferred to operate through a central point of control. For BGP based . For BGP-based
overlay flow services such as "Multicast VPN Using BIER" (<xref target="RFC8556" overlay flow services such as "<xref target="RFC8556" format="title"/>" <xref ta
/>) this rget="RFC8556" format="default"/>, this
can be achieved by making the BIER-TE controller operate as a BGP Route can be achieved by making the BIER-TE controller operate as a BGP Route
Reflector (<xref target="RFC4456"/>) and combining it with signaling through BGP Reflector <xref target="RFC4456" format="default"/> and combining it with signal
or a different protocol for the BIER-TE controller calculated BitStrings. ing through BGP
See <xref target="engineered-bitstrings"/> and <xref target="bitstring-mappings" or a different protocol for the BIER-TE controller's calculated BitStrings.
/>.</t> See Sections&nbsp;<xref target="engineered-bitstrings" format="counter"/> and <x
ref target="bitstring-mappings" format="counter"/>.</t>
</section> </section>
<!-- flow-overlay -->
<section anchor="control-plane" title="The BIER-TE Control Plane">
<t>In the (non-TE) BIER architecture <xref target="RFC8279"/>, the BIER control <section anchor="control-plane" numbered="true" toc="default">
plane is not explicitly separated from the BIER forwarding plane, <name>The BIER-TE Control Plane</name>
but instead their functions are summarized together in Section 4.2. <t>In the (non-TE) BIER architecture <xref target="RFC8279" format="defa
ult"/>, the BIER layer is summarized in <xref target="RFC8279" sectionFormat="of
" section="4.2"/>. This summary includes both the functions
of the BIER-layer control plane and forwarding plane, without using those terms.
Example standardized options for the BIER control plane include Example standardized options for the BIER control plane include
ISIS/OSPF extensions for BIER, <xref target="RFC8401"/> and <xref target="RFC844 IS-IS and OSPF extensions for BIER, as specified in <xref target="RFC8401" forma
4"/>.</t> t="default"/> and <xref target="RFC8444" format="default"/>, respectively.</t>
<t>For BIER-TE, the control plane includes, at a minimum, the following
<t>For BIER-TE, the control plane includes at minimum the following functionalit functionality.</t>
y.</t>
<t><list style="hanging">
<t anchor="topology-control" hangText="1. BIER-TE topology control:">During
initial provisioning of the network and/or during modifications of its topology
and/or services, the protocols and/or procedures to establish BIER-TE BIFTs:
<list style="numbers">
<t anchor="topology-control-1">Determine the desired BIER-TE topology fo
r a BIER-TE sub-domains: the native and/or overlay adjacencies that are assigned
to BPs. Topology discovery is discussed in <xref target="topology-discovery"/>
and the various aspects of the BIER-TE controllers determinations about the topo
logy are discussed throughout <xref target="controller-ops"/></t>
<t>Determine the per-BFR BIFT from the BIER-TE topology. This is achieve
d by simply extracting the adjacencies of the BFR from the BIER-TE topology and
populating the BFRs BIFT with them.</t>
<t>Optionally assign BFR-ids to BFIRs for later insertion into BIER head
ers on BFIRs as BFIR-id. Alternatively, BFIR-id in BIER packet headers may be ma
naged solely by the flow overlay layer and/or be unused. This is discussed in <x
ref target="bfr-id"/>.</t>
<t>Install/update the BIFTs into the BFRs and optionally BFR-ids into BF
IRs. This is discussed in <xref target="topology-discovery"/>.</t>
</list></t>
<t anchor="tree-control" hangText="2. BIER-TE tree control:">During operatio
ns of the network, protocols and/or procedures to support creation/change/remova
l of overlay flows on BFIRs:
<list style="numbers">
<t>Process the BIER-TE requirements for the multicast overlay flow: BFIR
and BFERs of the flow as well as policies for the path selection of the flow. T
his is discussed in <xref target="te-considerations"/>.</t>
<t>Determine the BitStrings and optionally Entropy. This is discussed in
<xref target="engineered-bitstrings"/>, <xref target="te-considerations"/> and
<xref target="bitstring-mappings"/>.</t>
<t>Install state on the BFIR to impose the desired BIER packet header(s)
for packets of the overlay flow. Different aspects of this and the next point a
re discussed throughout <xref target="bier-te-controller"/> and in <xref target=
"encapsulation"/>, but the main responsibility of these two points is with the M
ulticast Flow Overlay (<xref target="flow-overlay"/>), which is architecturally
inherited from BIER.</t>
<t>Install the necessary state on the BFERs to decapsulate the BIER pack
et header and properly dispatch its payload.</t>
</list></t>
</list></t>
<section anchor="bier-te-controller" title="The BIER-TE Controller">
<t>[RFC-Editor: the following text has three references to anchors topology-cont
rol, topology-control-1 and tree-control. Unfortunately, XMLv2 does not offer an
y tagging that reasonable references are generated (i had this problem already i
n RFCs last year. Please make sure there are useful-to-read cross-references in
the RFC in these three places after you convert to XMLv3.]</t>
<t>This architecture describes the <ol spacing="normal" type="1"><li>
BIER-TE control plane as shown in <xref target="architecture"/> to consist of:
<list style="symbols">
<t>A BIER-TE controller.</t>
<t>BFR data-models and protocols to communicate between controller and B
FRs
in support of <xref target="topology-control">BIER-TE topology contro
l</xref>,
such as YANG/NETCONF/RESTCONF (<xref target="RFC7950"/>/<xref target=
"RFC6241"/>/<xref target="RFC8040"/>).</t>
<t>BFR data-models and protocols to communicate between controller and B
FIR in support of
<xref target="tree-control">BIER-TE tree control</xref>, such as BIER
-TE extensions
for <xref target="RFC5440"/>.</t>
</list>
</t>
<t>The single, centralized BIER-TE controller is used in this document as refere <t>BIER-TE topology control: During initial provisioning of the networ
nce option for the BIER-TE control plane but other options are equally feasible. k and/or during modifications of its topology and/or services, the protocols and
/or procedures to establish BIER-TE BIFTs:</t>
<ol spacing="normal" type="%p%c">
<li anchor="topology-control-1">Determine the desired BIER-TE topo
logy for BIER-TE subdomains: the adjacencies that are assigned to BPs. Topology
discovery is discussed in <xref target="topology-discovery" format="default"/>,
and the various aspects of the BIER-TE controller's determinations regarding the
topology are discussed throughout <xref target="controller-ops" format="default
"/>.</li>
<li>Determine the per-BFR BIFT from the BIER-TE topology. This is
achieved by simply extracting the adjacencies of the BFR from the BIER-TE topolo
gy and populating the BFR's BIFT with them.</li>
<li>Optionally assign BFR-ids to BFIRs for later insertion into BI
ER headers on BFIRs as BFIR-ids. Alternatively, BFIR-ids in BIER packet headers
may be managed solely by the flow overlay layer and/or be unused. This is discus
sed in <xref target="bfr-id" format="default"/>.</li>
<li>Install/update the BIFTs into the BFRs and, optionally, BFR-id
s into BFIRs. This is discussed in <xref target="topology-discovery" format="def
ault"/>.</li>
</ol>
</li>
<li>
<t anchor="tree-control">
BIER-TE tree control:
During network operations, protocols and/or procedures to support cr
eation/change/removal of overlay flows on BFIRs:</t>
<ol spacing="normal" type="%p%c"><li>Process the BIER-TE requirement
s for the multicast overlay flow: BFIRs and BFERs of the flow as well as policie
s for the path selection of the flow. This is discussed in <xref target="te-cons
iderations" format="default"/>.</li>
<li>Determine the BitStrings and, optionally, entropy.
BitStrings are discussed in Sections&nbsp;<xref target="engineered-bitstrings" f
ormat="counter"/>, <xref target="te-considerations" format="counter"/>, and <xre
f target="bitstring-mappings" format="counter"/>. Entropy is discussed in <xref
target="forward-ecmp"/>.</li>
<li>Install state on the BFIR to impose the desired BIER packet he
ader(s) for packets of the overlay flow. Different aspects of this point, as wel
l as the next point, are discussed throughout <xref target="bier-te-controller"
format="default"/> and in <xref target="encapsulation" format="default"/>. The m
ain component responsible for these two points is the multicast flow overlay (<x
ref target="flow-overlay" format="default"/>), which is architecturally inherite
d from BIER.</li>
<li>Install the necessary state on the BFERs to decapsulate the BI
ER packet header and properly dispatch its payload.</li>
</ol>
</li>
</ol>
<section anchor="bier-te-controller" numbered="true" toc="default">
<name>The BIER-TE Controller</name>
<t>This architecture describes the
BIER-TE control plane, as shown in <xref target="architecture" format="default"/
>, as consisting of:
</t>
<ul spacing="normal">
<li>A BIER-TE controller.</li>
<li>BFR data models and protocols to communicate between the control
ler and BFRs
in support of <xref target="topology-control-1" format="none">BIER-TE
topology control</xref> (see the list under "BIER-TE topology control"),
such as YANG/NETCONF/RESTCONF <xref target="RFC7950" format="default"
/> <xref target="RFC6241" format="default"/> <xref target="RFC8040" format="defa
ult"/>.</li>
<li>BFR data models and protocols to communicate between the control
ler and BFIRs in support of
<xref target="tree-control" format="none">BIER-TE tree control</xref>
(see <xref target="control-plane"/>, point 2.), such as BIER-TE extensions
for <xref target="RFC5440" format="default"/>.</li>
</ul>
<t>The single, centralized BIER-TE controller is used in this document
as the reference option for the BIER-TE control plane, but other options are eq
ually feasible.
The BIER-TE control plane could equally be implemented without automated configu ration/protocols, The BIER-TE control plane could equally be implemented without automated configu ration/protocols,
by an operator via CLI on the BFRs. by an operator via a CLI on the BFRs.
In that case, operator configured local policy on the BFIR would have to In that case, operator-configured local policy on the BFIR would have to
determine how to set the appropriate BIER header fields. The BIER-TE control pl ane could also be decentralized determine how to set the appropriate BIER header fields. The BIER-TE control pl ane could also be decentralized
and/or distributed, but this document does not consider any additional protocols and/or procedures and/or distributed, but this document does not consider any additional protocols and/or procedures
which would then be necessary to coordinate its (distributed/decentralized) enti that would then be necessary to coordinate its (distributed/decentralized) entit
ties to achieve the above described functionality.</t> ies to achieve the above-described functionality.</t>
<section anchor="topology-discovery" numbered="true" toc="default">
<section anchor="topology-discovery" title="BIER-TE Topology discovery and <name>BIER-TE Topology Discovery and Creation</name>
creation"> <t>
<xref target="topology-control-1" format="none">The first item listed for BIER-T
<t><xref target="topology-control-1">The first item of BIER-TE topology control< E topology control</xref> (<xref target="control-plane"/>, point 1.a.)
/xref>
includes network topology discovery and BIER-TE topology creation. The latter de scribes includes network topology discovery and BIER-TE topology creation. The latter de scribes
the process by which a Controller determines which routers are to be configured as BFRs and the the process by which a controller determines which routers are to be configured as BFRs and the
adjacencies between them.</t> adjacencies between them.</t>
<t>In statically managed networks, e.g., industrial environments, bo
<t>In statically managed networks, such as in industrial environments, both disc th discovery and creation can be a manual/offline process.</t>
overy and creation can be a manual/offline process.</t> <t>In other networks, topology discovery may rely on such protocols
as those that include extending an IGP based on a link-state protocol into the B
<t>In other networks, topology discovery may rely on protocols including extendi IER-TE controller itself, e.g., BGP-LS <xref target="RFC7752" format="default"/>
ng a "Link-State-Protocol" based IGP into the BIER-TE controller itself, <xref t or YANG topology <xref target="RFC8345" format="default"/>, as well as methods
arget="RFC7752"/> (BGP-LS) or <xref target="RFC8345"/> (YANG topology) as well a specific to BIER-TE -- for example, via <xref target="BIER-TE-YANG" format="defa
s BIER-TE specific methods, for example via <xref target="I-D.ietf-bier-te-yang" ult"/>. These options are non-exhaustive.</t>
/>. These options are non-exhaustive.</t> <t>Dynamic creation of the BIER-TE topology can be as easy as mappin
g the network topology 1:1 to the BIER-TE topology by assigning a BP for every n
<t>Dynamic creation of the BIER-TE topology can be as easy as mapping the networ etwork subnet adjacency. In larger networks, it likely involves more complex pol
k topology 1:1 to the BIER-TE topology by assigning a BP for every network subne icy and optimization decisions, including how to minimize the number of BPs requ
t adjacency. In larger networks, it likely involves more complex policy and opti ired and how to assign BPs across different BitStrings to minimize the number of
mization decisions including how to minimize the number of BPs required and how duplicate packets across links when delivering an overlay flow to BFERs using d
to assign BPs across different BitStrings to minimize the number of duplicate pa ifferent SIs:BitStrings. These topics are discussed in <xref target="controller-
ckets across links when delivering an overlay flow to BFER using different SIs/B ops" format="default"/>.</t>
itStrings. These topics are discussed in <xref target="controller-ops"/>.</t> <t>When the BIER-TE topology has been determined, the BIER-TE contro
ller pushes
<t>When the BIER-TE topology is determined, the BIER-TE Controller then pushes the BPs/adjacencies to the BIFT of the BFRs. On each BFR, only those SIs:BPs
the BitPositions/adjacencies to the BIFT of the BFRs. On each BFR only those SI: that are adjacencies to other BFRs in the BIER-TE topology are populated.</t>
BitPositions <t>Communications between the BIER-TE controller and BFRs for both B
are populated that are adjacencies to other BFRs in the BIER-TE topology.</t> IER-TE topology
control and BIER-TE tree control are ideally via standardized protocols and data
<t>Communications between the BIER-TE Controller and BFRs for both BIER-TE topol models such
ogy as NETCONF/RESTCONF/YANG/PCEP. A vendor-specific CLI on the BFRs is also an opt
control and BIER-TE tree control is ideally via standardized protocols and data- ion (as in many other "Software-Defined Network" (SDN)
models such solutions lacking definitions of standardized data models).</t>
as NETCONF/RESTCONF/YANG/PCEP. Vendor-specific CLI on the BFRs is also an optio </section>
n (as in many other SDN <section anchor="engineered-bitstrings" numbered="true" toc="default">
solutions lacking definition of standardized data models).</t> <name>Engineered Trees via BitStrings</name>
<t>In BIER, the same set of BFERs in a single subdomain is always en
</section> coded as the same BitString.
In BIER-TE, the BitString used to reach the same set of BFERs in the same subdom
<section anchor="engineered-bitstrings" title="Engineered Trees via BitStr ain can be
ings"> different for different overlay flows because the BitString encodes the paths to
wards the BFERs,
<t>In BIER, the same set of BFER in a single sub-domain is always encoded as the so the BitStrings from different BFIRs to the same set of BFERs will often be di
same BitString. fferent. Likewise, the BitString from
In BIER-TE, the BitString used to reach the same set of BFER in the same sub-dom the same BFIR to the same set of BFERs can be different for different
ain can be overlay flows if different policies should be applied to those overlay
different for different overlay flows because the BitString encodes the paths to flows, such as shortest path trees, Steiner
wards the BFER, trees (minimum cost trees), diverse path trees for redundancy, and so on.
so the BitStrings from different BFIR to the same set of BFER will often be diff </t>
erent. <t>See also <xref target="BIER-MCAST-OVERLAY" format="default"/> for
Likewise, the BitString from the same BFIR to the same set of BFER can be differ an application
ent for different overlay
flows for policy reasons such as shortest path trees, Steiner trees (minimum cos
t trees),
diverse path trees for redundancy and so on.</t>
<t>See also <xref target="I-D.ietf-bier-multicast-http-response"/> for an applic
ation
leveraging BIER-TE engineered trees.</t> leveraging BIER-TE engineered trees.</t>
</section>
<section anchor="changes-in-topo" numbered="true" toc="default">
<name>Changes in the Network Topology</name>
<t>If the network topology changes (not failure based) so that adjac
encies
that are assigned to bit positions are no longer needed, the BIER-TE controller
can
reuse those bit positions for new adjacencies. First, these bit positions
need to be removed from any BFIR flow state and BFR BIFT state. Then, they
can be repopulated, first into the BIFT and then into the BFIR.</t>
</section>
</section> <section anchor="failures" numbered="true" toc="default">
<name>Link/Node Failures and Recovery</name>
<section anchor="changes-in-topo" title="Changes in the network topology"> <t>When links or nodes fail or recover in the topology, BIER-TE coul
d quickly
<t>If the network topology changes (not failure based) so that adjacencies respond with "Fast Reroute" (FRR) procedures such as those described in <xref ta
that are assigned to bit positions are no longer needed, the BIER-TE Controller rget="BIER-TE-PROTECTION" format="default"/>, the details of which are out of sc
can ope for this document. It can also more slowly react by
re-use those bit positions for new adjacencies. First, these bit positions
need to be removed from any BFIR flow state and BFR BIFT state, then they
can be repopulated, first into BIFT and then into the BFIR.</t>
</section>
<!-- changes-in-topo -->
<section anchor="failures" title="Link/Node Failures and Recovery">
<t>When link or nodes fail or recover in the topology, BIER-TE could quickly
respond with FRR procedures such as <xref target="I-D.eckert-bier-te-frr"/>, the
details of which are out of scope for this document. It can also more slowly re
act by
recalculating the BitStrings of affected multicast flows. This reaction is recalculating the BitStrings of affected multicast flows. This reaction is
slower than the FRR procedure because the BIER-TE Controller needs to receive slower than the FRR procedure because the BIER-TE controller needs to receive
link/node up/down indications, recalculate the desired BitStrings and push link/node up/down indications, recalculate the desired BitStrings, and push
them down into the BFIRs. With FRR, this is all performed locally on a BFR them down into the BFIRs. With FRR, this is all performed locally on a BFR
receiving the adjacency up/down notification.</t> receiving the adjacency up/down notification.</t>
</section>
</section>
<!-- failures -->
</section> </section>
<!-- control-plane -->
</section> </section>
<!-- XXX -->
<section anchor="forwarding-plane" title="The BIER-TE Forwarding Plane"> <section anchor="forwarding-plane" numbered="true" toc="default">
<name>The BIER-TE Forwarding Plane</name>
<t>[RFC-editor Q: "is constituted from" / "consists of" / "composed from..." ??? <t>The BIER-TE forwarding plane consists of the following components:
]</t> </t>
<t>The BIER-TE Forwarding Plane is constituted from the following components: <ol spacing="normal" type="1"><li>On a BFIR, imposition of the BIER head
<list style="numbers"> er for packets from overlay flows. This is driven by state established by the BI
<t>On a BFIR, imposition of the BIER header for packets from overlay flo ER-TE control plane, the multicast flow overlay as explained in <xref target="fl
ws. This is driven by a combination of state established by the BIER-TE control ow-overlay" format="default"/>, or a combination of both.</li>
plane and/or the multicast flow overlay as explained in <xref target="flow-overl <li>On BFRs (including BFIRs and BFERs), forwarding/replication of BIE
ay"/>.</t> R packets according to their SD, SI, "BitStringLength" (BSL), BitString, and, op
<t>On BFRs (including BFIR and BFER), forwarding/replication of BIER pac tionally, entropy fields as explained in <xref target="forwarding" format="defau
kets according to their SD, SI, "BitStringLength" (BSL), BitString and optionall lt"/>. Processing of other BIER header fields, such as the "Differentiated Servi
y Entropy fields as explained in <xref target="forwarding"/>. Processing of othe ces Code Point" (DSCP) field, is outside the scope of this document.</li>
r BIER header fields such as DSCP is outside the scope of this document.</t> <li>On BFERs, removal of the BIER header and dispatching of the payloa
<t>On BFERs, removal of the BIER header and dispatching of the payload a d according to state created by the BIER-TE control plane and/or overlay layer.<
ccording to state created by the BIER-TE control plane and/or overlay layer.</t> /li>
</list> </ol>
</t> <t>When the BIER-TE forwarding plane receives a packet, it simply looks
<t>When the BIER-TE Forwarding Plane receives a packet, it simply looks
up the bit positions that are set in the BitString of the packet in the up the bit positions that are set in the BitString of the packet in the
BIFT that was populated by the BIER-TE Controller. BIFT that was populated by the BIER-TE controller.
For every BP that is set in the BitString, and that has one or For every BP that is set in the BitString and has one or
more adjacencies in the BIFT, a copy is made according to the type more adjacencies in the BIFT, a copy is made according to the types
of adjacencies for that BP in the BIFT. Before sending any copy, the of adjacencies for that BP in the BIFT. Before sending any copies, the
BFR clears all BPs in the BitString of the packet for which the BFR clears all BPs in the BitString of the packet for which the
BFR has one or more adjacencies in the BIFT. Clearing these bits inhibits BFR has one or more adjacencies in the BIFT. Clearing these bits prevents
packets from looping when the BitStrings erroneously includes a forwarding loop. packets from looping when a BitString erroneously includes a forwarding loop.
When a forward_connected() adjacency has the "DoNotClear" (DNC) flag When a forward_connected() adjacency has the "DoNotClear" (DNC) flag
set, then this BP is re-set for the packet copied to that adjacency. set, this BP is reset for the packet copied to that adjacency.
See <xref target="forward-connected"/>.</t> See <xref target="forward-connected" format="default"/>.</t>
</section>
</section>
<!-- forwarding-plane -->
<section anchor="routing-underlay" title="The Routing Underlay">
<t>For forward_connected() adjacencies, BIER-TE is sending BIER packets to direc <section anchor="routing-underlay" numbered="true" toc="default">
tly connected <name>The Routing Underlay</name>
BIER-TE neighbors as L2 (unicasted) BIER packets without requiring a <t>For forward_connected() adjacencies, BIER-TE sends BIER packets to di
rectly connected
BIER-TE neighbors as L2 (unicast) BIER packets without requiring a
routing underlay. For forward_routed() adjacencies, BIER-TE forwarding encapsula tes routing underlay. For forward_routed() adjacencies, BIER-TE forwarding encapsula tes
a copy of the BIER packet so that it can be delivered by the forwarding plane a copy of the BIER packet so that it can be delivered by the forwarding plane
of the routing underlay to the routable destination address indicated in the adj acency. of the routing underlay to the routable destination address indicated in the adj acency.
See <xref target="forward-routed"/> for the adjacency definition.</t> See <xref target="forward-routed" format="default"/> for details on forward_rout
ed() adjacencies.</t>
<t>BIER relies on the routing underlay to calculate paths towards BFERs and deri <t>BIER relies on the routing underlay to calculate paths towards BFERs
ve and derive next-hop BFR adjacencies for those paths. These two steps commonly re
next-hop BFR adjacencies for those paths. This commonly relies on BIER specific ly on BIER-specific extensions to the routing protocols of the routing underlay
extensions but may also be established
to the routing protocols of the routing underlay but may also be established by a controller. In BIER-TE, the next hops for a packet are determined by the Bi
by a controller. In BIER-TE, the next-hops of a packet are determined by the Bit tString
String through the BIER-TE controller-established adjacencies on the BFR for the BPs of
through the BIER-TE Controller established adjacencies on the BFR for the BPs of the BitString.
the BitString. There is thus no need for BFR-specific routing underlay extensions to forward BI
There is thus no need for BFR specific routing underlay extensions to forward BI ER packets with
ER packets with
BIER-TE semantics.</t> BIER-TE semantics.</t>
<t>Encapsulation parameters can be provisioned by the BIER-TE controller
<t>Encapsulation parameters can be provisioned by the BIER-TE controller into into
the forward_connected() or forward_routed() adjacencies directly without relying on a routing underlay. the forward_connected() or forward_routed() adjacencies directly without relying on a routing underlay.
</t> </t>
<t>If the BFR intends to support FRR for BIER-TE, then the BIER-TE
<t>If the BFR intends to support FRR for BIER-TE, then the BIER-TE
forwarding plane needs to receive fast adjacency up/down notifications: forwarding plane needs to receive fast adjacency up/down notifications:
Link up/down or neighbor up/down, e.g. from BFD. Providing these notifications link up/down or neighbor up/down, e.g., from "Bidirectional Forwarding Detection " (BFD). Providing these notifications
is considered to be part of the routing underlay in this document.</t> is considered to be part of the routing underlay in this document.</t>
</section>
</section> <section anchor="te-considerations" numbered="true" toc="default">
<!-- routing-underlay --> <name>Traffic Engineering Considerations</name>
<t>Traffic Engineering <xref target="TE-OVERVIEW" format="default"/>
<section anchor="te-considerations" title="Traffic Engineering Consideration
s">
<t>Traffic Engineering (<xref target="I-D.ietf-teas-rfc3272bis"/>)
provides performance optimization of operational IP networks while utilizing provides performance optimization of operational IP networks while utilizing
network resources economically and network resources economically and
reliably. The key elements needed to effect TE are policy, path steering reliably. The key elements needed to effect Traffic Engineering are policy, pat h steering,
and resource management. These elements require support at the and resource management. These elements require support at the
control/controller level and within the forwarding plane.</t> control/controller level and within the forwarding plane.</t>
<t>Policy decisions are made within the BIER-TE control plane, i.e., wit
<t>Policy decisions are made within the BIER-TE control plane, i.e., within hin
BIER-TE Controllers. Controllers use policy when composing BitStrings BIER-TE controllers. Controllers use policy when composing BitStrings
and BFR BIFT state. The mapping of user/IP traffic to specific and BFR BIFT state. The mapping of user/IP traffic to specific
BitStrings/BIER-TE flows is made based on policy. The specific details of BitStrings / BIER-TE flows is made based on policy. The specific details of
BIER-TE policies and how a controller uses them are out of scope of this BIER-TE policies and how a controller uses them are out of scope for this
document.</t> document.</t>
<t>Path steering is supported via the definition of a BitString. BitStr
<t>Path steering is supported via the definition of a BitString. BitStrings ings
used in BIER-TE are composed based on policy and resource management used in BIER-TE are composed based on policy and resource management
considerations. For example, when composing BIER-TE BitStrings, a Controller mu st take considerations. For example, when composing BIER-TE BitStrings, a controller mu st take
into account the resources available at each BFR and for each BP into account the resources available at each BFR and for each BP
when it is providing congestion-loss-free services such as when it is providing congestion-loss-free services such as
Rate Controlled Service Disciplines <xref target="RCSD94"/>. Resource availabil Rate-Controlled Service Disciplines <xref target="RCSD94" format="default"/>. R
ity esource availability
could be provided for example via routing protocol information, but could be provided, for example, via routing protocol information but
may also be obtained via a BIER-TE control protocol such as NETCONF or may also be obtained via a BIER-TE control protocol such as NETCONF or
any other protocol commonly used by a Controller to understand the resources any other protocol commonly used by a controller to understand the resources
of the network it operates on. The of the network on which it operates. The
resource usage of the BIER-TE traffic admitted by the BIER-TE controller resource usage of the BIER-TE traffic admitted by the BIER-TE controller
can be solely tracked on the BIER-TE Controller based on local accounting can be solely tracked on the BIER-TE controller based on local accounting
as long as no forward_routed() adjacencies are used (see <xref target="forward-c as long as no forward_routed() adjacencies are used (see <xref target="forward-r
onnected"/> for the definition outed" format="default"/> for the definition
of forward_routed() adjacencies). When forward_routed() adjacencies are used, of forward_routed() adjacencies). When forward_routed() adjacencies are used,
the paths selected by the underlying routing protocol need to be tracked as well .</t> the paths selected by the underlying routing protocol need to be tracked as well .</t>
<t>Resource management has implications for the forwarding plane beyond
<t>Resource management has implications on the forwarding plane beyond the BIER-TE-defined steering of packets; this includes allocation of
the BIER-TE defined steering of packets. This includes allocation of buffers to guarantee the worst-case requirements for admitted RCSD traffic
buffers to guarantee the worst case requirements of admitted RCSD traffic
and potentially policing and/or rate-shaping mechanisms, typically done and potentially policing and/or rate-shaping mechanisms, typically done
via various forms of queuing. This level of resource control, via various forms of queuing. This level of resource control,
while optional, is important in networks that wish to while optional, is important in networks that wish to
support congestion management policies to control or regulate the offered support congestion management policies to control or regulate the offered
traffic to deliver different levels of service and alleviate congestion traffic to deliver different levels of service and alleviate congestion
problems, or those networks that wish to control latencies experienced by problems, or those networks that wish to control latencies experienced by
specific traffic flows.</t> specific traffic flows.</t>
</section>
</section> </section>
<!-- te-considerations -->
</section>
<!-- components -->
<section anchor="forwarding" title="BIER-TE Forwarding">
<section anchor="btft" title="The BIER-TE Bit Index Forwarding Table (BIFT)" <section anchor="forwarding" numbered="true" toc="default">
> <name>BIER-TE Forwarding</name>
<section anchor="btft" numbered="true" toc="default">
<t>The BIER-TE BIFT is the equivalent to the BIER BIFT for (non-TE) BIER. It <name>The BIER-TE Bit Index Forwarding Table (BIFT)</name>
exists on every BFR running BIER-TE. For every BIER sub-domain (SD) in use for B <t>The BIER-TE BIFT is equivalent to the (non-TE) BIER BIFT. It
IER-TE, exists on every BFR running BIER-TE. For every BIER "subdomain" (SD) in use for
it is a table as shown shown in <xref target="adjacencies"/>. That example BIER-TE,
BIFT assumes a BSL of 8 bit positions (BPs) in the packets BitString. the BIFT is constructed per the example shown in <xref target="adjacencies" form
As in <xref target="RFC8279"/> this BSL is purely used for the example and not a at="default"/>. The
BIER/BIER-TE BIFT in the figure assumes a BSL of 8 "bit positions" (BPs) in the packets BitSt
supported BSL (minimum BSL is 64).</t> ring.
As in <xref target="RFC8279" format="default"/>, this BSL is purely used as an e
<t>A BIER-TE BIFT compares to a BIER BIFT as shown in <xref target="RFC8279"/> a xample and is not a BSL supported by BIER/BIER-TE
s (minimum BSL is 64).</t>
<t>A BIER-TE BIFT is compared to a BIER BIFT as shown in <xref target="R
FC8279" format="default"/> as
follows.</t> follows.</t>
<t>In both BIER and BIER-TE, BIFT rows/entries are indexed in their resp
<t>In both BIER and BIER-TE, BIFT rows/entries are indexed in their respective B ective BIER pseudocode
IER pseudocode (<xref target="RFC8279" sectionFormat="comma" section="6.5"/>) and BIER-TE pseud
(<xref target="RFC8279"/> Section 6.5) and BIER-TE pseudocode (<xref target="pse ocode (<xref target="pseudocode" format="default"/>)
udocode"/>) by the BIFT-index derived from the packet's SI, BSL, and the one bit position of
by the BIFT-index derived from the packets SI, BSL and the one bit position of t the
he
packets BitString (BP) addressing the BIFT row: BIFT-index = SI * BSL + BP - 1. packets BitString (BP) addressing the BIFT row: BIFT-index = SI * BSL + BP - 1.
BP within a BitString are numbered from 1 to BSL, hence the - 1 offset when conv BPs within a BitString are numbered from 1 to BSL -- hence, the - 1 offset when
erting converting
to a BIFT-index. This document also uses the notion SI:BP to indicate BIFT rows, to a BIFT-index. This document also uses the notion "SI:BP" to indicate BIFT row
<xref target="RFC8279"/> uses the equivalent notion SI:BitString, where the BitS s.
tring is <xref target="RFC8279" format="default"/> uses the equivalent notion "SI:BitStri
filled with only the BP for the BIFT row.</t> ng", where the BitString is
filled with only the BPs for the BIFT row.</t>
<t>In BIER, each BIFT-index addresses one BFER by its BFR-id = BIFT-index + 1 <t>In BIER, each BIFT-index addresses one BFER by its BFR-id = BIFT-inde
x + 1
and is populated on each BFR with the next-hop "BFR Neighbor" (BFR-NBR) towards that BFER.</t> and is populated on each BFR with the next-hop "BFR Neighbor" (BFR-NBR) towards that BFER.</t>
<t>In BIER-TE, each BIFT-index and, therefore, SI:BP indicates one or, i
n the case of reuse of SI:BP, more than one adjacency between BFRs in the topolo
gy. The SI:BP
is populated with the adjacency on the upstream BFR of the adjacency. The BIFT
entries are empty on all other BFRs.</t>
<t>In BIER, each BIFT row also requires a "Forwarding Bit Mask" (F-BM) e
ntry
for BIER forwarding rules. In BIER-TE forwarding, an F-BM is not required but ca
n be used
when implementing BIER-TE on forwarding hardware, derived from BIER forwarding,
that
must use an F-BM. This is discussed in the first variation of BIER-TE forwarding
pseudocode shown in
<xref target="pseudocode" format="default"/>.</t>
<t>In BIER-TE, each BIFT-index and therefore SI:BP indicates one or more adjacen <figure anchor="adjacencies">
cies <name>BIER-TE Bit Index Forwarding Table (BIFT) with Different Adjacencies</name
between BFRs in the topology and is only populated with those adjacencies forwa >
rding
entries on the BFR that is the upstream for these adjacencies. The BIFT entry ar
e
empty on all other BFRs.</t>
<t>In BIER, each BIFT row also requires a "Forwarding Bit Mask" (F-BM) entry
for BIER forwarding rules. In BIER-TE forwarding, F-BM is not required, but can
be used
when implementing BIER-TE on forwarding hardware derived from BIER forwarding, t
hat
must use F-BM. This is discussed in the first BIER-TE forwarding pseudocode in
<xref target="pseudocode"/>.</t>
<figure anchor="adjacencies" title="BIER-TE BIFT with different adjacencies">
<artwork align="left"><![CDATA[ <artwork align="left"><![CDATA[
------------------------------------------------------------------ -------------------------------------------------------------------
| BIFT-index | | Adjacencies: | | BIFT-index | | Adjacencies: |
| (SI:BP) |(FBM)| <empty> or one or more per entry | | (SI:BP) |(F-BM)| <empty> or one or more per entry |
================================================================== ===================================================================
| BIFT indices for Packets with SI=0 | | BIFT indices for Packets with SI=0 |
------------------------------------------------------------------ -------------------------------------------------------------------
| 0 (0:1) | ... | forward_connected(interface,neighbor{,DNC}) | | 0 (0:1) | ... | forward_connected(interface,neighbor{,DNC}) |
------------------------------------------------------------------ -------------------------------------------------------------------
| 1 (0:2) | ... | forward_connected(interface,neighbor{,DNC}) | | 1 (0:2) | ... | forward_connected(interface,neighbor{,DNC}) |
| | ... | forward_connected(interface,neighbor{,DNC}) | | | ... | forward_connected(interface,neighbor{,DNC}) |
------------------------------------------------------------------ -------------------------------------------------------------------
| ... | ... | ... | | ... | ... | ... |
------------------------------------------------------------------ -------------------------------------------------------------------
| 4 (0:5) | ... | local_decap({VRF}) | | 4 (0:5) | ... | local_decap({VRF}) |
------------------------------------------------------------------ -------------------------------------------------------------------
| 5 (0:6) | ... | forward_routed({VRF,}l3-neighbor) | | 5 (0:6) | ... | forward_routed({VRF,}l3-neighbor) |
------------------------------------------------------------------ -------------------------------------------------------------------
| 6 (0:7) | ... | <empty> | | 6 (0:7) | ... | <empty> |
------------------------------------------------------------------ -------------------------------------------------------------------
| 7 (0:8) | ... | ECMP((adjacency1,...adjacencyN){,seed}) | | 7 (0:8) | ... | ECMP((adjacency1,...adjacencyN){,seed}) |
----------------------------------------------------------------- -------------------------------------------------------------------
| BIFT indices for BitString/Packet with SI=1 | | BIFT indices for BitString/Packet with SI=1 |
------------------------------------------------------------------ -------------------------------------------------------------------
| 9 (1:1) | | ... | | 9 (1:1) | | ... |
| ... |... | ... | | ... | ... | ... |
------------------------------------------------------------------ -------------------------------------------------------------------
BIER-TE Bit Index Forwarding Table (BIFT)
]]></artwork></figure> ]]></artwork></figure>
<t>The BIFT is configured for the BIER-TE data plane of a BFR by the BIE
<t>The BIFT is configured for the BIER-TE data plane of a BFR by the BIER-TE R-TE
Controller through an appropriate protocol and data-model. The BIFT is then controller through an appropriate protocol and data model. The BIFT is then
used to forward packets, according to the rules used to forward packets, according to the procedures for the BIER-TE forwarding
specified in the BIER-TE Forwarding Procedures.</t> plane as specified in <xref target="forwarding-plane"/>.</t>
<t>Note that a BIFT-index (SI:BP) may be populated in the BIFT of more
<t>Note that a BIFT index (SI:BP) may be populated in the BIFT of more than one BFR to save BPs. See <xref target="rings" format="default"/> for an exa
than one BFR to save BPs. See <xref target="rings"/> for an example of how a BIE mple of how a BIER-TE controller
R-TE controller
could assign BPs to (logical) adjacencies shared across multiple BFRs, could assign BPs to (logical) adjacencies shared across multiple BFRs,
<xref target="leaf-bfer"/> for an example of assigning the same BP to different <xref target="leaf-bfer" format="default"/> for an example of assigning the same
adjacencies, and <xref target="reuse"/> for general guidelines regarding re-use BP to different
of BPs across different adjacencies.</t> adjacencies, and <xref target="reuse" format="default"/> for general guidelines
regarding the reuse of BPs across different adjacencies.</t>
<t>{VRF} indicates the Virtual Routing and Forwarding context into which <t>{VRF} indicates the Virtual Routing and Forwarding context into which
the BIER payload is to be delivered. This is optional and depends the BIER payload is to be delivered. This is optional and depends
on the multicast flow overlay.</t> on the multicast flow overlay.</t>
</section>
</section> <section anchor="atypes" numbered="true" toc="default">
<!-- btft --> <name>Adjacency Types</name>
<section anchor="forward-connected" numbered="true" toc="default">
<section anchor="atypes" title="Adjacency Types"> <name>Forward Connected</name>
<t>A "forward_connected()" adjacency is an adjacency towards a directl
<section anchor="forward-connected" title="Forward Connected"> y connected
BFR-NBR using an interface address of that BFR on the connecting
<t>A "forward_connected()" adjacency is towards a directly connected interface. A forward_connected() adjacency does not route packets;
BFR neighbor using an interface address of that BFR on the connecting only L2 forwards them to the neighbor.</t>
interface. A forward_connected() adjacency does not route packets <t>Packets sent to an adjacency with "DoNotClear" (DNC) set in the
but only L2 forwards them to the neighbor.</t> BIFT <bcp14>MUST NOT</bcp14> have the bit position for that adjacency cleared wh
en the
<t>Packets sent to an adjacency with "DoNotClear" (DNC) set in the
BIFT MUST NOT have the bit position for that adjacency cleared when the
BFR creates a copy for it. The bit position will still be cleared for BFR creates a copy for it. The bit position will still be cleared for
copies of the packet made towards other adjacencies. This can be copies of a packet made towards other adjacencies. This can be
used for example in ring topologies as explained in <xref target="rings"/>.</t> used, for example, in ring topologies as explained in <xref target="rings" forma
t="default"/>.</t>
<t>For protection against loops from misconfiguration (see <xref target="loops"/ <t>For protection against loops caused by misconfiguration (see <xref
>), target="loops" format="default"/>),
DNC is only permissible for forward_connected() adjacencies. No need or benefit DNC is only permissible for forward_connected() adjacencies. No need or benefit
of DNC for other type of adjacencies was identified and their risk was not analy of DNC for other types of adjacencies was identified, and associated risks were
zed.</t> not analyzed.</t>
</section>
</section>
<!-- forward-connected -->
<section anchor="forward-routed" title="Forward Routed">
<t>A "forward_routed()" adjacency is an adjacency towards a BFR that <section anchor="forward-routed" numbered="true" toc="default">
uses a (tunneling) encapsulation which will cause the packet to be <name>Forward Routed</name>
forwarded by the routing underlay toward the adjacent BFR. This can <t>A "forward_routed()" adjacency is an adjacency towards a BFR that
uses a (tunneling) encapsulation that will cause a packet to be
forwarded by the routing underlay towards the adjacent BFR indicated via the l3-
neighbor parameter of the forward_routed() adjacency. This can
leverage any feasible encapsulation, such as MPLS or tunneling over IP/IPv6, leverage any feasible encapsulation, such as MPLS or tunneling over IP/IPv6,
as long as the BIER-TE packet can be identified as a payload. This identificatio n as long as the BIER-TE packet can be identified as a payload. This identificatio n
can either rely on the BIER/BIER-TE co-existence mechanisms described in can rely on either the BIER/BIER-TE co-existence mechanisms described in
<xref target="encapsulation"/>, or by explicit support for a BIER-TE payload typ <xref target="encapsulation" format="default"/> or explicit support for a BIER-T
e E payload type
in the tunneling encapsulation.</t> in the tunneling encapsulation.</t>
<t>Forward_routed() adjacencies are necessary to pass BIER-TE traffic
across
routers that are not BIER-TE capable or to minimize the number of required BPs b
y
tunneling over (BIER-TE-capable) routers on which neither replication nor
path steering is desired, or simply to leverage the routing underlay's path redu
ndancy and FRR towards the next BFR. They may also be useful to a
multi-subnet adjacent BFR for leveraging the routing underlay ECMP
independently of BIER-TE ECMP (<xref target="forward-ecmp" format="default"/>).<
/t>
</section>
<t>forward_routed() adjacencies are necessary to pass BIER-TE traffic across <section anchor="forward-ecmp" numbered="true" toc="default">
non BIER-TE capable routers or to minimize the number of required BP by <name>ECMP</name>
tunneling over (BIER-TE capable) routers on which neither replication nor <t>(Non-TE) BIER ECMP is tied to the BIER BIFT processing semantic and
path-steering is desired, or simply to leverage path redundancy and FRR of the is therefore
routing underlay towards the next BFR. They may also be useful to a
multi-subnet adjacent BFR to leverage the routing underlay ECMP
independent of BIER-TE ECMP (<xref target="forward-ecmp"/>).</t>
</section>
<!-- forward-routed -->
<section anchor="forward-ecmp" title="ECMP">
<t>(non-TE) BIER ECMP is tied to the BIER BIFT processing semantic and is theref
ore
not directly usable with BIER-TE.</t> not directly usable with BIER-TE.</t>
<t>A BIER-TE "Equal-Cost Multipath" (ECMP()) adjacency as shown in <xr
<t>A BIER-TE "Equal Cost Multipath" (ECMP()) adjacency as shown in <xref target= ef target="adjacencies" format="default"/>
"adjacencies"/> for BIFT-index 7 has a list of two or more non-ECMP() adjacencies as parameters
for BIFT-index 7 has a list of two or more non-ECMP adjacencies as parameters an and an optional
d an optional
seed parameter. When a BIER-TE packet is copied seed parameter. When a BIER-TE packet is copied
onto such an ECMP() adjacency, an implementation specific so-called hash functio n onto such an ECMP() adjacency, an implementation-specific so-called hash functio n
will select one out of the list's adjacencies to which the packet is forwarded. will select one out of the list's adjacencies to which the packet is forwarded.
If the packet's encapsulation contains an entropy field, the entropy field SHOUL If the packet's encapsulation contains an entropy field, the entropy field <bcp1
D 4>SHOULD</bcp14>
be respected; two packets with the same value of the entropy field SHOULD be sen be respected; two packets with the same value of the entropy field <bcp14>SHOULD
t on </bcp14> be sent on
the same adjacency. The seed parameter allows to design the same adjacency. The seed parameter permits the design of
hash functions that are easy to implement at high speed without running into hash functions that are easy to implement at high speed without running into
polarization issues across multiple consecutive ECMP hops. See <xref target="ecm polarization issues across multiple consecutive ECMP hops. See <xref target="ecm
p"/> p" format="default"/>
for more explanations.</t> for details.</t>
</section>
</section>
<!-- forward-ecmp -->
<section anchor="forward-local" title="Local Decap(sulation)">
<t>A "local_decap()" adjacency passes a copy of the payload of <section anchor="forward-local" numbered="true" toc="default">
the BIER-TE packet to the protocol ("NextProto") within the BFR (IPv4/IPv6, Ethe <name>Local Decap(sulation)</name>
rnet,...) responsible for <t>A "local_decap()" adjacency passes a copy of the payload of
the BIER-TE packet to the protocol ("NextProto") within the BFR (IP/IPv6, Ethern
et,...) responsible for
that payload according to the packet header fields. that payload according to the packet header fields.
A local_decap() adjacency turns the BFR into a BFER for matching A local_decap() adjacency turns the BFR into a BFER for matching
packets. Local_decap() adjacencies require the BFER to support packets. Local_decap() adjacencies require the BFER to support
routing or switching for NextProto to determine how to further routing or switching for NextProto to determine how to further
process the packet.</t> process the packets.</t>
</section>
</section>
<!-- forward-local -->
</section> </section>
<!-- atypes -->
<section anchor="encapsulation" title="Encapsulation / Co-existence with BIE <section anchor="encapsulation" numbered="true" toc="default">
R"> <name>Encapsulation / Co-existence with BIER</name>
<t>Specifications for BIER-TE encapsulation are outside the scope of thi
<t>Specifications for BIER-TE encapsulation are outside the scope of this docume s document.
nt.
This section gives explanations and guidelines.</t> This section gives explanations and guidelines.</t>
<t>The handling of "Maximum Transmission Unit" (MTU) limitations is
<t>Like <xref target="RFC8279"/>, handling of "Maximum Transmission Unit" (MTU) outside the scope of this document and is not discussed in
limitations is outside the scope of this document and instead part of the <xref target="RFC8279" format="default"/> either. Instead, this process is part
BIER-TE packet encapsulation and/or flow overlay. See for example <xref target=" of the BIER-TE packet encapsulation and/or flow overlay; for example, see
RFC8296"/>, Section 3. <xref target="RFC8296" sectionFormat="comma" section="3"/>.
It applies equally to BIER-TE as it does to BIER.</t> It applies equally to BIER-TE and BIER.</t>
<t>Because a BFR needs to interpret the BitString of a BIER-TE packet di
<t>Because a BFR needs to interpret the BitString of a BIER-TE packet differentl fferently
y from a (non-TE) BIER packet, it is necessary to distinguish BIER packets from BI
from a (non-TE) BIER packet, it is necessary to distinguish BIER from BIER-TE pa ER-TE packets.
ckets. In BIER encapsulation <xref target="RFC8296" format="default"/>,
In the BIER encapsulation <xref target="RFC8296"/>,
the BIFT-id field of the packet indicates the BIFT of the packet. BIER and BIER- TE can the BIFT-id field of the packet indicates the BIFT of the packet. BIER and BIER- TE can
therefore be run simultaneously, when the BIFT-id address space is shared across therefore be run simultaneously, when the BIFT-id address space is shared across
BIER BIFT and BIER-TE BIFT. Partitioning the BIFT-id address space is subject BIER BIFTs and BIER-TE BIFTs. Partitioning the BIFT-id address space is subject
to BIER-TE/BIER control plane procedures.</t> to BIER-TE/BIER control plane procedures.</t>
<t>When <xref target="RFC8296" format="default"/> is used for BIER with
<t>When <xref target="RFC8296"/> is used for BIER with MPLS, BIFT-id address ran MPLS, BIFT-id address ranges
ges
can be dynamically allocated from MPLS label space only for the set of actually can be dynamically allocated from MPLS label space only for the set of actually
used SD:BSL BIFT. This allows to also allocate non-overlapping label ranges for BIFT-id used SD:BSL BIFTs. This also permits the allocation of non-overlapping label ra nges for BIFT-ids
that are to be used with BIER-TE BIFTs.</t> that are to be used with BIER-TE BIFTs.</t>
<t>With MPLS, it is also possible to reuse the
<t>With MPLS, it is also possible to reuse the
same SD space for both BIER-TE and BIER, so that the same SD has both a same SD space for both BIER-TE and BIER, so that the same SD has both a
BIER BIFT with a corresponding range of BIFT-ids and disjoint BIER-TE BIFTs with a non-overlapping range of BIFT-ids.</t> BIER BIFT with a corresponding range of BIFT-ids and disjoint BIER-TE BIFTs with a non-overlapping range of BIFT-ids.</t>
<t>Assume that a fixed mapping from BSL, SD, and SI to a BIFT-id is used
<t>When a fixed mapping from BSL, SD and SI to BIFT-id is used which does ,
not explicitly partition the BIFT-id space between BIER and BIER-TE, which does not explicitly partition the BIFT-id space between BIER
such as proposed for non-MPLS forwarding with <xref target="RFC8296"/> encapsula and BIER-TE -- for example, as proposed for non-MPLS forwarding with
tion BIER encapsulation <xref target="RFC8296" format="default"/>
in <xref target="I-D.ietf-bier-non-mpls-bift-encoding"/> in <xref target="NON-MPLS-BIER-ENCODING" sectionFormat="comma" section="5"/>.
revision 04, section 5, then it is necessary to allocate disjoint SDs to BIER In this case, it is necessary to allocate disjoint SDs to BIER and BIER-TE BIFTs
and BIER-TE BIFTs so that both can be addressed by the BIFT-ids. The encoding so that both can be addressed by the BIFT-ids. The encoding
proposed in section 6. of the same document does not statically encode BSL proposed in <xref target="NON-MPLS-BIER-ENCODING" sectionFormat="of" section="6"
or SD into the BIFT-id, but allows for a mapping, and hence could provide for /> does not statically encode the BSL or SD into the BIFT-id, but the encoding
the same freedom as when MPLS is being used (same or different SD for BIER/BIER- permits a mapping and hence could provide the same freedom as when
TE).</t> MPLS is being used (the same SD, or different SDs for BIER/BIER-TE).
</t>
<t>forward_routed() requires an encapsulation that permits to direct unicast enc <t>Forward_routed() requires an encapsulation that permits directing uni
apsulated BIER-TE packets to a specific interface address on a target BFR. With cast encapsulated BIER-TE packets to a specific interface address on a target BF
MPLS encapsulation, this can R. With MPLS encapsulation, this can
simply be done via a label stack with that addresses label as the top label - fo simply be done via a label stack with that address's label as the top label, fol
llowed lowed
by the label assigned to the (BSL,SD,SI) BitString. by the label assigned to the (BSL,SD,SI) BitString.
With non-MPLS encapsulation, some form of IP encapsulation would be required (fo r example IP/GRE). With non-MPLS encapsulation, some form of IP encapsulation would be required (fo r example, IP/GRE).
</t> </t>
<t>The encapsulation used for forward_routed() adjacencies can equally s
upport
existing advanced adjacency information such as "loose source routes" via, for e
xample, MPLS
label stacks or appropriate header extensions (e.g., for IPv6).</t>
</section>
<t>The encapsulation used for forward_routed() adjacencies can equally support <section anchor="pseudocode" numbered="true" toc="default">
existing advanced adjacency information such as "loose source routes" via e.g. M <name>BIER-TE Forwarding Pseudocode</name>
PLS <t>
label stacks or appropriate header extensions (e.g. for IPv6).</t> The pseudocode for BIER-TE forwarding, as shown in <xref target="simple-pseudoco
de-picture" format="default"/>, is based
</section> on the (non-TE) BIER forwarding pseudocode provided in <xref target="RFC8279" se
<!-- encapsulation --> ctionFormat="comma" section="6.5"/>, with one modification.</t>
<figure anchor="simple-pseudocode-picture">
<section anchor="pseudocode" title="BIER-TE Forwarding Pseudocode"> <name>BIER-TE Forwarding Pseudocode for Required Functions, Based on B
IER Pseudocode</name>
<t> <sourcecode name="" type="pseudocode"><![CDATA[
The following pseudocode, <xref target="simple-pseudocode-picture"/>, for BIER-T
E forwarding is based
on the (non-TE) BIER forwarding pseudocode of <xref target="RFC8279"/>, section
6.5 with one modification.</t>
<figure anchor="simple-pseudocode-picture" title="BIER-TE Forwarding Pseudocode
for required functions, based on BIER Pseudocode">
<artwork align="left"><![CDATA[
void ForwardBitMaskPacket_withTE (Packet) void ForwardBitMaskPacket_withTE (Packet)
{ {
SI=GetPacketSI(Packet); SI=GetPacketSI(Packet);
Offset=SI*BitStringLength; Offset=SI*BitStringLength;
for (Index = GetFirstBitPosition(Packet->BitString); Index ; for (Index = GetFirstBitPosition(Packet->BitString); Index ;
Index = GetNextBitPosition(Packet->BitString, Index)) { Index = GetNextBitPosition(Packet->BitString, Index)) {
F-BM = BIFT[Index+Offset]->F-BM; F-BM = BIFT[Index+Offset]->F-BM;
if (!F-BM) continue; [3] if (!F-BM) continue; [3]
BFR-NBR = BIFT[Index+Offset]->BFR-NBR; BFR-NBR = BIFT[Index+Offset]->BFR-NBR;
PacketCopy = Copy(Packet); PacketCopy = Copy(Packet);
PacketCopy->BitString &= F-BM; [2] PacketCopy->BitString &= F-BM; [2]
PacketSend(PacketCopy, BFR-NBR); PacketSend(PacketCopy, BFR-NBR);
// The following must not be done for BIER-TE: // The following must not be done for BIER-TE:
// Packet->BitString &= ~F-BM; [1] // Packet->BitString &= ~F-BM; [1]
} }
} }
]]></artwork></figure> ]]></sourcecode>
</figure>
<t>In step [2], the F-BM is used to clear bit(s) in PacketCopy. <t>In step [2], the F-BM is used to clear one or more bits in PacketCopy
.
This step exists in both BIER and BIER-TE, but the F-BMs need to be This step exists in both BIER and BIER-TE, but the F-BMs need to be
populated differently for BIER-TE than for BIER for the desired clearing.</t> populated differently for BIER-TE than for BIER for the desired clearing.</t>
<t>In BIER, multiple bits of a BitString can have the same BFR-NBR.
<t>In BIER, multiple bits of a BitString can have the same BFR-NBR.
When a received packets BitString has more than one of those bits set, When a received packets BitString has more than one of those bits set,
the BIER replication logic has to avoid that more than one PacketCopy is BIER's replication logic has to prevent more than one PacketCopy from being
sent to that BFR-NBR ([1]). Likewise, the PacketCopy sent to a BFR-NBR sent to that BFR-NBR ([1]). Likewise, the PacketCopy sent to a BFR-NBR
must clear all bits in its BitString that are not routed across BFR-NBR. must clear all bits in its BitString that are not routed across a BFR-NBR.
This protects against BIER replication on any possible further This prevents BIER's replication logic from creating duplicates on any possible
BFR to create duplicates ([2]).</t> further BFRs ([2]).</t>
<t>To solve both [1] and [2] for BIER, the F-BM of each bit index needs
<t>To solve both [1] and [2] for BIER, the F-BM of each bit index needs to have to have all
all bits set that this BFR wants to route across a BFR-NBR. &nbsp;[2] clears
bits set that this BFR wants to route across BFR-NBR. [2] clears all other bits in PacketCopy-&gt;BitString, and [1] clears those bits from
all other bits in PacketCopy->BitString, and [1] clears those bits from Packet-&gt;BitString after the first PacketCopy.</t>
Packet->BitString after the first PacketCopy.</t> <t>In BIER-TE, a BFR-NBR in this pseudocode is an adjacency -- forward_c
onnected(), forward_routed(),
<t>In BIER-TE, a BFR-NBR in this pseudocode is an adjacency, forward_connected() or local_decap(). There is no need for [2] to suppress duplicates in the same wa
, forward_routed() y
or local_decap(). There is no need for [2] to suppress duplicates in the way that BIER does, because in general, different BPs would never have the same
BIER does because in general, different BP would never have the same
adjacency. If a BIER-TE controller actually finds some optimization in adjacency. If a BIER-TE controller actually finds some optimization in
which this would be desirable, then the controller is also responsible to which this would be desirable, then the controller is also responsible for
ensure that only one of those bits is set in any Packet->BitString, unless ensuring that only one of those bits is set in any Packet-&gt;BitString, unless
the controller explicitly wants for duplicates to be created.</t> the controller explicitly wants duplicates to be created.</t>
<t>The following points describe how the F-BM for each BP is configured
<t>The following points describe how the forwarding bit mask (F-BM) for each BP in the BIFT and how this impacts the BitString of the packet being processed wit
is configured in the BIFT and how this impacts the BitString of the packet being h that BIFT:
processed with that BIFT: </t>
<list style="numbers"> <ol spacing="normal" type="1"><li>The F-BMs of all BIFT BPs without an a
<t>The F-BMs of all BIFT BPs without an adjacency have all their bits clear. djacency have all their bits clear.
This will cause [3] to skip further processing of such a BP.</t> This will cause [3] to skip further processing of such a BP.</li>
<t>All BIFT BPs with an adjacency (with DNC flag clear) have an F-BM <li>All BIFT BPs with an adjacency (with the DNC flag clear) have an F
-BM
that has only those BPs set for which this BFR does not have an adjacency. that has only those BPs set for which this BFR does not have an adjacency.
This causes [2] to clear all bits from PacketCopy->BitString for which this This causes [2] to clear all bits from PacketCopy-&gt;BitString for which this
BFR does have an adjacency.</t> BFR does have an adjacency.</li>
<t>[1] is not performed for BIER-TE. All bit clearing required by BIER-TE <li>[1] is not performed for BIER-TE. All bit clearing required by BIE
is performed by [2].</t> R-TE
</list></t> is performed by [2].</li>
</ol>
<t>This Forwarding Pseudocode can support the required BIER-TE forwarding <t>This forwarding pseudocode can support the required BIER-TE forwardin
functions (see <xref target="requirements"/>), forward_connected(), g
forward_routed() and local_decap(), but not the recommended functions DNC flag functions (see <xref target="requirements" format="default"/>) -- forward_connec
and multiple adjacencies per bit nor the optional function, ECMP() adjacencies. ted(),
forward_routed(), and local_decap() -- but cannot support the recommended functi
ons (DNC flag and multiple adjacencies per bit) or the optional function (i.e.,
ECMP() adjacencies).
The DNC flag cannot be supported when using only [1] to mask bits.</t> The DNC flag cannot be supported when using only [1] to mask bits.</t>
<t>The modified and expanded forwarding pseudocode in <xref target="pseu
<t>The modified and expanded Forwarding Pseudocode in <xref target="pseudocode-p docode-picture" format="default"/> specifies how to
icture"/> specifies how to support all BIER-TE forwarding functions (required, recommended, and optional):
support all BIER-TE forwarding functions (required, recommended and optional): </t>
<list style="symbols"> <ol spacing="normal">
<t>This pseudocode eliminates per-bit F-BM, therefore reducing the size of B <li>
IFT state by BSL^2*SI and eliminating the need for per-packet-copy BitString mas <t>This pseudocode eliminates per-bit F-BMs, therefore reducing the
king operations except for adjacencies with the DNC flag set: size of BIFT state by SI*BSL<sup>2</sup> and eliminating the need for per-packet
<list style="symbols"> -copy BitString masking operations, except for adjacencies with the DNC flag set
<t>AdjacentBits[SI] are bit positions with a non-empty list of adjacenci :
es in this BFR BIFT. This can be computed whenever the BIER-TE Controller update </t>
s (add/removes) adjacencies in the BIFT.</t> <ol spacing="normal" type="%p%c">
<t>The BFR needs to create packet copies for these adjacent bits when th <li>AdjacentBits[SI] are bit positions with a non-empty list of ad
ey are set in the packets BitString. This set of bits is calculated in PktAdjace jacencies in this BFR BIFT. This can be computed whenever the BIER-TE controller
ntBits.</t> updates (adds/removes) adjacencies in the BIFT.</li>
<t>All bit positions to which the BFR creates copies have to be cleared <li>The BFR needs to create packet copies for these adjacent bits
in packet copies to avoid loops. This is done by masking the BitString of the pa when they are set in the packets BitString. This set of bits is calculated in Pk
cket with ~AdjacentBits[SI]. When an adjacency has DNC set, this bit position is tAdjacentBits.</li>
set again only for the packet copy towards that bit position.</t> <li>All bit positions for which the BFR creates copies have to be
</list></t> cleared in packet copies to avoid loops. This is done by masking the BitString o
<t>BIFT entries may contain more than one adjacency in support of specific c f the packet with ~AdjacentBits[SI]. When an adjacency has DNC set, this bit pos
onfigurations such as <xref target="hubnspoke"/>. The code therefore includes a ition is set again only for the packet copy towards that bit position.</li>
loop over these adjacencies.</t> </ol>
<t>The ECMP() adjacency is shown. Its parameters are a seed and a ListOfAdja </li>
cencies from which one is picked.</t> <li>BIFT entries may contain more than one adjacency in support of spe
<t>The forward_connected(), forward_routed(), local_decap() adjacencies are cific configurations, such as a hub and multiple spokes (<xref target="hubnspoke
shown with their parameters.</t> " format="default"/>). The code therefore includes a loop over these adjacencies
</list></t> .</li>
<li>The ECMP() adjacency is also shown in the figure. Its parameters a
<figure anchor="pseudocode-picture" title="Complete BIER-TE Forwarding Pseudocod re a seed and "ListOfAdjacencies", from which one is picked.</li>
e for required, recommended and optional functions"> <li>The forward_connected(), forward_routed(), and local_decap() adjac
<artwork align="left"><![CDATA[ encies are shown with their parameters.</li>
</ol>
<figure anchor="pseudocode-picture">
<name>Complete BIER-TE Forwarding Pseudocode for Required, Recommended
, and Optional Functions</name>
<sourcecode name="" type="pseudocode"><![CDATA[
void ForwardBitMaskPacket_withTE (Packet) void ForwardBitMaskPacket_withTE (Packet)
{ {
SI = GetPacketSI(Packet); SI = GetPacketSI(Packet);
Offset = SI * BitStringLength; Offset = SI * BitStringLength;
// Determine adjacent bits in the Packets BitString // Determine adjacent bits in the packets BitString
PktAdjacentBits = Packet->BitString & AdjacentBits[SI]; PktAdjacentBits = Packet->BitString & AdjacentBits[SI];
// Clear adjacent bits in Packet header to avoid loops // Clear adjacent bits in the packet header to avoid loops
Packet->BitString &= ~AdjacentBits[SI]; Packet->BitString &= ~AdjacentBits[SI];
// Loop over PktAdjacentBits to create packet copies // Loop over PktAdjacentBits to create packet copies
for (Index = GetFirstBitPosition(PktAdjacentBits); Index ; for (Index = GetFirstBitPosition(PktAdjacentBits); Index ;
Index = GetNextBitPosition(PktAdjacentBits, Index)) { Index = GetNextBitPosition(PktAdjacentBits, Index)) {
for adjacency in BIFT[Index+Offset]->Adjacencies { for adjacency in BIFT[Index+Offset]->Adjacencies {
if(adjacency.type == ECMP(ListOfAdjacencies,seed) ) { if(adjacency.type == ECMP(ListOfAdjacencies,seed) ) {
I = ECMP_hash(sizeof(ListOfAdjacencies), I = ECMP_hash(sizeof(ListOfAdjacencies),
Packet->Entropy,seed); Packet->Entropy,seed);
adjacency = ListOfAdjacencies[I]; adjacency = ListOfAdjacencies[I];
skipping to change at line 1074 skipping to change at line 902
case forward_routed({VRF,}l3-neighbor): case forward_routed({VRF,}l3-neighbor):
SendToL3(PacketCopy,{VRF,}l3-neighbor); SendToL3(PacketCopy,{VRF,}l3-neighbor);
case local_decap({VRF},neighbor): case local_decap({VRF},neighbor):
DecapBierHeader(PacketCopy); DecapBierHeader(PacketCopy);
PassTo(PacketCopy,{VRF,}Packet->NextProto); PassTo(PacketCopy,{VRF,}Packet->NextProto);
} }
} }
} }
} }
]]></artwork></figure> ]]></sourcecode>
</figure>
</section> </section>
<!-- pseudocode -->
<section anchor="requirements" title="BFR Requirements for BIER-TE forwarding">
<t>BFR that support BIER-TE and BIER MUST support configuration that enables
BIER-TE instead of (non-TE) BIER forwarding rules for all BIFT of one or more
BIER sub-domains. Every BP in a BIER-TE BIFT MUST support to have
zero or one adjacency. BIER-TE forwarding MUST support the adjacency types forwa
rd_connected() with the DNC flag not set, forward_routed() and local_decap().
As explained in <xref target="pseudocode"/>, these required BIER-TE forwarding f
unctions
can be implemented via the same Forwarding Pseudocode as BIER forwarding except
for
one modification (skipping one masking with F-BM).</t>
<t>BIER-TE forwarding SHOULD support forward_connected() adjacencies with a set
DNC flag,
as this is highly useful to save bits in rings (see <xref target="rings"/>).</t>
<t>BIER-TE forwarding SHOULD support more than one adjacency on a bit.
This allows to save bits in hub and spoke scenarios (see <xref target="hubnspoke
"/>).</t>
<t>BIER-TE forwarding MAY support ECMP() adjacencies to save bits in ECMP <section anchor="requirements" numbered="true" toc="default">
scenarios, see <xref target="ecmp"/> for an example. <name>BFR Requirements for BIER-TE Forwarding</name>
<t>BFRs that support BIER-TE and BIER <bcp14>MUST</bcp14> support a conf
iguration that enables
BIER-TE instead of (non-TE) BIER forwarding rules for all BIFTs of one or more
BIER subdomains. Every BP in a BIER-TE BIFT <bcp14>MUST</bcp14> support having
zero or one adjacency. BIER-TE forwarding <bcp14>MUST</bcp14> support the adjace
ncy types forward_connected() with the DNC flag not set, forward_routed(), and l
ocal_decap().
As explained in <xref target="pseudocode" format="default"/>, these required BIE
R-TE forwarding functions
can be implemented via the same forwarding pseudocode as that used for BIER forw
arding, except for
one modification (skipping one masking with an F-BM).</t>
<t>BIER-TE forwarding <bcp14>SHOULD</bcp14> support forward_connected()
adjacencies with the DNC flag set,
as this is very useful for saving bits in rings (see <xref target="rings" format
="default"/>).</t>
<t>BIER-TE forwarding <bcp14>SHOULD</bcp14> support more than one adjace
ncy on a bit.
This allows bits to be saved in hub-and-spoke scenarios (see <xref target="hubns
poke" format="default"/>).</t>
<t>BIER-TE forwarding <bcp14>MAY</bcp14> support ECMP() adjacencies to s
ave bits in ECMP
scenarios; see <xref target="ecmp" format="default"/> for an example.
This is an optional requirement, because for ECMP deployments using BIER-TE This is an optional requirement, because for ECMP deployments using BIER-TE
one can also leverage ECMP of the routing underlay via forwarded_routed one can also leverage the routing underlay ECMP via forward_routed()
adjacencies and/or might prefer to have more explicit control of the path adjacencies and/or might prefer to have more explicit control of the path
chosen via explicit BP/adjacencies for each ECMP path alternative.</t> chosen via explicit BPs/adjacencies for each ECMP path alternative.</t>
</section>
</section> </section>
</section> <section anchor="controller-ops" numbered="true" toc="default">
<!-- forwarding --> <name>BIER-TE Controller Operational Considerations</name>
<section anchor="bitpositions" numbered="true" toc="default">
<section anchor="controller-ops" title="BIER-TE Controller Operational Considera <name>Bit Position Assignments</name>
tions"> <t>This section describes how the BIER-TE controller can use the
<section anchor="bitpositions" title="Bit Position Assignments">
<t>This section describes how the BIER-TE Controller can use the
different BIER-TE adjacency types to define the bit positions of a BIER-TE domai n.</t> different BIER-TE adjacency types to define the bit positions of a BIER-TE domai n.</t>
<t>Because the size of the BitString limits the size of the
<t>Because the size of the BitString limits the size of the BIER-TE domain, many of the options described here exist to support larger
BIER-TE domain, many of the options described exist to support larger
topologies with fewer bit positions.</t> topologies with fewer bit positions.</t>
<section anchor="p2p-links" numbered="true" toc="default">
<section anchor="p2p-links" title="P2P Links"> <name>P2P Links</name>
<t>On a "point-to-point" (P2P) link that connects two BFRs, the same b
<t>On a P2P link that connects two BFRs, the same bit position can be used on it position can be used on
both BFRs for the adjacency to the neighboring BFR. A P2P link requires therefor both BFRs for the adjacency to the neighboring BFR. A P2P link therefore require
e s
only one bit position.</t> only one bit position.</t>
</section>
</section> <section anchor="bfer" numbered="true" toc="default">
<!-- p2p-links --> <name>BFERs</name>
<t>Every non-leaf BFER is given a unique bit position with a local_dec
<section anchor="bfer" title="BFER"> ap() adjacency.</t>
</section>
<t>Every non-Leaf BFER is given a unique bit position with a local_decap() adjac
ency.</t>
</section>
<!-- bfer -->
<section anchor="leaf-bfer" title="Leaf BFERs">
<figure anchor="leaf-bfer-picture" title="Leaf vs. non-Leaf BFER Example"> <section anchor="leaf-bfer" numbered="true" toc="default">
<artwork align="left"><![CDATA[ <name>Leaf BFERs</name>
<t>A leaf BFER is one where incoming BIER-TE packets never need to
be forwarded to another BFR but are only sent to the BFER
to exit the BIER-TE domain. For example, in networks where "Provider Edge" (PE)
routers
are spokes connected to Provider (P) routers, those PEs are leaf BFERs, unless
there is a U-turn between two PEs.</t>
<t>Consider how redundant disjoint
traffic can reach BFER1/BFER2 as shown in <xref target="leaf-bfer-picture" forma
t="default"/>: when BFER1/BFER2
are non-leaf BFERs as shown on the right-hand side, one traffic
copy would be forwarded to BFER1 from BFR1, but the other one
could only reach BFER1 via BFER2, which makes BFER2 a non-leaf
BFER. Likewise, BFER1 is a non-leaf BFER when forwarding traffic to BFER2.
Note that the BFERs on the left-hand side of the figure are only guaranteed to
be leaf BFERs by correctly applying a routing configuration that prohibits trans
it
traffic from passing through the BFERs, which is commonly applied in these
topologies.</t>
<figure anchor="leaf-bfer-picture">
<name>Leaf vs. Non-Leaf BFER Example</name>
<artwork align="left" name="" type="" alt=""><![CDATA[
BFR1(P) BFR2(P) BFR1(P) BFR2(P) BFR1(P) BFR2(P) BFR1(P) BFR2(P)
| \ / | | | | \ / | | |
| X | | | | X | | |
| / \ | | | | / \ | | |
BFER1(PE) BFER2(PE) BFER1(PE)----BFER2(PE) BFER1(PE) BFER2(PE) BFER1(PE)----BFER2(PE)
^ U-turn link ^ U-turn link
Leaf BFER / Non-Leaf BFER / Leaf BFER / Non-leaf BFER /
PE-router PE-router PE router PE router
]]></artwork></figure> ]]></artwork>
</figure>
<t>A leaf BFER is one where incoming BIER-TE packets never need to <t>In most situations, leaf BFERs that are to be addressed via the sam
be forwarded to another BFR but are only sent to the BFER e BitString can share a single bit position for their local_decap() adjacency in
to exit the BIER-TE domain. For example, in networks where Provider Edge (PE) ro that BitString and therefore save bit positions. On a non-leaf BFER, a received
uter BIER-TE packet may only need to transit the BFER, or it may also need to be dec
are spokes connected to Provider (P) routers, those PEs are Leaf BFERs unless apsulated. Whether or not to decapsulate the packet therefore needs to be indica
there is a U-turn between two PEs.</t> ted by a unique bit position populated only on the BIFT of this BFER with a loca
l_decap() adjacency. On a leaf BFER, packets never need to pass through; any pac
<t>Consider how redundant disjoint ket received is therefore usually intended to be decapsulated. This can be expre
traffic can reach BFER1/BFER2 in <xref target="leaf-bfer-picture"/>: When BFER1/ ssed by a single, shared bit position that is populated with a local_decap() adj
BFER2 acency on all leaf BFERs addressed by the BitString.</t>
are Non-Leaf BFER as shown on the right-hand side, one traffic <t>The possible exceptions to this leaf BFER bit position optimization
copy would be forwarded to BFER1 from BFR1, but the other one scenario can be cases where the bit position on the prior BIER-TE BFR (which cr
could only reach BFER1 via BFER2, which makes BFER2 a non-Leaf eated the packet copy for the leaf BFER in question) is populated with multiple
BFER. Likewise, BFER1 is a non-Leaf BFER when forwarding traffic to BFER2. adjacencies as an optimization -- for example, as described in Sections&nbsp;<xr
Note that the BFERs in the left-hand picture are only guaranteed to ef target="lans" format="counter"/> and <xref target="hubnspoke" format="counter
be leaf-BFER by fitting routing configuration that prohibits transit "/>. With either of these two optimizations, the sender of the packet could only
traffic to pass through the BFERs, which is commonly applied in these control explicitly whether the packet was to be decapsulated on the leaf BFER i
topologies.</t> n question, if the leaf BFER has a unique bit position for its local_decap() adj
acency.</t>
<t>In most situations, leaf-BFER that are to be addressed via the same BitString <t>However, if the bit position is shared across a leaf BFER and packe
can share a single bit position for their local_decap() adjacency in that BitSt ts are therefore decapsulated -- potentially unnecessarily -- this may still be
ring and therefore save bit positions. On a non-leaf BFER, a received BIER-TE pa appropriate if the decapsulated payload of the BIER-TE packet indicates whether
cket may only need to transit the BFER or it may need to also be decapsulated. W or not the packets need to be further processed/received. This is typically true
hether or not to decapsulate the packet therefore needs to be indicated by a uni , for example, if the payload is IP multicast, because IP multicast on a BFER wo
que bit position populated only on the BIFT of this BFER with a local_decap() ad uld know the membership state of the IP multicast payload and be able to discard
jacency. On a leaf-BFER, packets never need to pass through; any packet received it if the packets were delivered unnecessarily by the BIER-TE layer. If the pay
is therefore usually intended to be decapsulated. This can be expressed by a si load has no such membership indication and the BFIR wants to have explicit contr
ngle, shared bit position that is populated with a local_decap() adjacency on al ol regarding which BFERs are to receive and decapsulate a packet, then these two
l leaf-BFER addressed by the BitString.</t> optimizations cannot be used together with shared bit position optimization for
a leaf BFER.</t>
<t>The possible exception from this leaf-BFER bit position optimization can be c </section>
ases where the bit position on the prior BIER-TE BFR (which created the packet c
opy for the leaf-BFER in question) is populated with multiple adjacencies as an
optimization, such as in <xref target="lans"/> or <xref target="hubnspoke"/>. Wi
th either of these two optimizations, the sender of the packet could only contro
l explicitly whether the packet was to be decapsulated on the leaf-BFER in quest
ion, if the leaf-BFER has a unique bit position for its local_decap() adjacency.
</t>
<t>However, if the bit position is shared across leaf-BFER, and packets are ther
efore decapsulated potentially unnecessarily, this may still be appropriate if t
he decapsulated payload of the BIER-TE packet indicates whether or not the packe
t needs to be further processed/received. This is typically true for example if
the payload is IP multicast because IP multicast on a BFER would know the member
ship state of the IP multicast payload and be able to discard it if the packet w
as delivered unnecessarily by the BIER-TE layer. If the payload has no such memb
ership indication, and the BFIR wants to have explicit control about which BFER
are to receive and decapsulate a packet, then these two optimizations can not be
used together with shared bit positions optimization for leaf-BFER.</t>
</section>
<!-- leaf-bfer -->
<section anchor="lans" title="LANs">
<t>In a LAN, the adjacency to each neighboring BFR <section anchor="lans" numbered="true" toc="default">
<name>LANs</name>
<t>In a LAN, the adjacency to each neighboring BFR
is given a unique bit position. The adjacency of this bit position is given a unique bit position. The adjacency of this bit position
is a forward_connected() adjacency towards the BFR and this bit position is a forward_connected() adjacency towards the BFR, and this bit position
is populated into the BIFT of all the other BFRs on that LAN.</t> is populated into the BIFT of all the other BFRs on that LAN.</t>
<figure anchor="lan-picture">
<figure anchor="lan-picture" title="LAN Example"> <name>LAN Example</name>
<artwork align="left"><![CDATA[ <artwork align="left" name="" type="" alt=""><![CDATA[
BFR1 BFR1
|p1 |p1
LAN1-+-+---+-----+ LAN1-+-+---+-----+
p3| p4| p2| p3| p4| p2|
BFR3 BFR4 BFR7 BFR3 BFR4 BFR7
]]></artwork></figure> ]]></artwork>
</figure>
<t>If Bandwidth on the LAN is not an issue and most BIER-TE traffic <t>If bandwidth on the LAN is not an issue and most BIER-TE traffic
should be copied to all neighbors on a LAN, then bit positions should be copied to all neighbors on a LAN, then bit positions
can be saved by assigning just a single bit position to the LAN can be saved by assigning just a single bit position to the LAN
and populating the bit position of the BIFTs of each BFRs on and populating the bit position of the BIFTs of each BFR on
the LAN with a list of forward_connected() adjacencies to all other the LAN with a list of forward_connected() adjacencies to all other
neighbors on the LAN.</t> neighbors on the LAN.</t>
<t>This optimization does not work in the case of BFRs redundantly
connected to more than one LAN with this optimization. These
BFRs would receive duplicates and forward those duplicates into the
other LANs. Such BFRs require separate bit positions for each LAN they
connect to.</t>
</section>
<t>This optimization does not work in the case of BFRs redundantly <section anchor="hubnspoke" numbered="true" toc="default">
connected to more than one LAN with this optimization because <name>Hub and Spoke</name>
these BFRs would receive duplicates and forward those duplicates into <t>In a setup with a hub and multiple spokes connected via separate
the opposite LANs. Adjacencies of such BFRs into their LAN still P2P links to the hub, all P2P adjacencies from the hub to the spokes' links can
need a separate bit position.</t> share the same bit position.
The bit position on the hub's BIFT is set up with a list of
</section> forward_connected() adjacencies, one for each spoke.</t>
<!-- lans --> <t>This option is similar to the bit position optimization in
LANs: redundantly connected spokes need their own bit positions,
<section anchor="hubnspoke" title="Hub and Spoke"> unless they are themselves leaf BFERs.</t>
<t>This type of optimized BP could be used, for example, when all
<t>In a setup with a hub and multiple spokes connected via separate traffic is "broadcast" traffic (very dense receiver sets),
p2p links to the hub, all p2p adjacencies from the hub to the spokes links can s such as live TV or many-to-many telemetry, including situational awareness.
hare the same bit position.
The bit position on the hub's BIFT is set up with a list of
forward_connected() adjacencies, one for each Spoke.</t>
<t>This option is similar to the bit position optimization in
LANs: Redundantly connected spokes need their own bit positions,
unless they are themselves Leaf-BFER.</t>
<t>This type of optimized BP could be used for example when all
traffic is "broadcast" traffic (very dense receiver set)
such as live-TV or many-to-many telemetry including situation-awareness (SA).
This BP optimization can then be used to explicitly steer different traffic This BP optimization can then be used to explicitly steer different traffic
flows across different ECMP paths in Data-Center or broadband-aggregation flows across different ECMP paths in data-center or broadband-aggregation
networks with minimal use of BPs.</t> networks with minimal use of BPs.</t>
</section>
</section> <section anchor="rings" numbered="true" toc="default">
<!-- hubnspoke --> <name>Rings</name>
<t>In L3 rings, instead of assigning a single bit position for
<section anchor="rings" title="Rings"> every P2P link in the ring, it is possible to save bit positions by
<t>In L3 rings, instead of assigning a single bit position for
every p2p link in the ring, it is possible to save bit positions by
setting the "DoNotClear" (DNC) flag on forward_connected() adjacencies.</t> setting the "DoNotClear" (DNC) flag on forward_connected() adjacencies.</t>
<t>For the ring shown in <xref target="ring-picture" format="default"/
<t>For the rings shown in <xref target="ring-picture"/>, a single bit position >, a single bit position
will suffice to forward traffic entering the ring at BFRa or BFRb will suffice to forward traffic entering the ring at BFRa or BFRb
all the way up to BFR1:</t> all the way up to BFR1, as follows.</t>
<t>On BFRa, BFRb, BFR30,... BFR3, the bit position is populated with
<t>On BFRa, BFRb, BFR30,... BFR3, the bit position is populated with
a forward_connected() adjacency pointing to the clockwise neighbor a forward_connected() adjacency pointing to the clockwise neighbor
on the ring and with DNC set. On BFR2, the adjacency also points on the ring and with DNC set. On BFR2, the adjacency also points
to the clockwise neighbor BFR1, but without DNC set.</t> to the clockwise neighbor BFR1, but without DNC set.</t>
<t>Handling DNC this way ensures that copies forwarded from any BFRs i
<t>Handling DNC this way ensures that copies forwarded from any BFR in n
the ring to a BFR outside the ring will not have the ring bit position set, the ring to a BFR outside the ring will not have the ring bit position set,
therefore minimizing the chance to create loops.</t> therefore minimizing the risk of creating loops.</t>
<figure anchor="ring-picture">
<figure anchor="ring-picture" title="Ring Example"> <name>Ring Example</name>
<artwork align="left"><![CDATA[ <artwork align="left" name="" type="" alt=""><![CDATA[
v v v v
| | | |
L1 | L2 | L3 L1 | L2 | L3
/-------- BFRa ---- BFRb --------------------\ /-------- BFRa ---- BFRb --------------------\
| | | |
\- BFR1 - BFR2 - BFR3 - ... - BFR29 - BFR30 -/ \- BFR1 - BFR2 - BFR3 - ... - BFR29 - BFR30 -/
| | L4 | | | | L4 | |
p33| p15| p33| p15|
BFRd BFRc BFRd BFRc
]]></artwork></figure> ]]></artwork>
</figure>
<t>Note that this example only permits for packets intended to make it all <t>Note that this example only permits packets intended to make it all
the way around the ring to enter it at the way around the ring to enter it at
BFRa and BFRb, and that packets will always travel clockwise. If BFRa and BFRb. Note also that packets will always travel clockwise. If
packets should be allowed to enter the ring at any ring BFR, then one packets should be allowed to enter the ring at any of the ring's BFRs, then one
would have to use two ring bit positions. One for each direction: would have to use two ring bit positions, one for each direction:
clockwise and counterclockwise.</t> clockwise and counterclockwise.</t>
<t>Both would be set up to stop rotating on the same link, e.g., L1. W
<t>Both would be set up to stop rotating on the same link, e.g. L1. When the hen the
ingress ring BFR creates the clockwise copy, it will clear the counterclockwise ring's BFIR creates the clockwise copy, it will clear the counterclockwise
bit position because the DNC bit only applies to the bit for which the bit position because the DNC bit only applies to the bit for which the
replication is done. Likewise for the clockwise replication is done (likewise for the clockwise
bit position for the counterclockwise copy. As a result, the ring ingress bit position for the counterclockwise copy). As a result, the ring's
BFR will send a copy in both directions, serving BFRs on either side of the BFIR will send a copy in both directions, serving BFRs on either side of the
ring up to L1.</t> ring up to L1.</t>
</section>
</section> <section anchor="ecmp" numbered="true" toc="default">
<!-- rings --> <name>Equal-Cost Multipath (ECMP)</name>
<t>An ECMP() adjacency allows the use of just one BP to deliver packet
<section anchor="ecmp" title="Equal Cost MultiPath (ECMP)"> s
<t>[RFC-Editor: A reviewer (Lars Eggert) noted that the infinite "to use" in the
following sentence is not correct. The same was also noted for several other si
milar instances. The following URL seems to indicate though that this is a per-c
ase decision, which seems undefined: https://writingcenter.gmu.edu/guides/choosi
ng-between-infinitive-and-gerund-to-do-or-doing. What exactly should be done abo
ut this ?].</t>
<t>An ECMP() adjacency allows to use just one BP to deliver packets
to one of N adjacencies instead of one BP for each adjacency. to one of N adjacencies instead of one BP for each adjacency.
In the common example case <xref target="ecmp-picture"/>, In the common example case shown in <xref target="ecmp-picture" format="default"
a link-bundle of three links L1,L2,L3 connects BFR1 and BFR2, and />,
only one BP is used instead of three BP to deliver packets from a link bundle of three links L1,L2,L3 connects BFR1 and BFR2, and
only one BP is used instead of three BPs to deliver packets from
BFR1 to BFR2.</t> BFR1 to BFR2.</t>
<figure anchor="ecmp-picture">
<figure anchor="ecmp-picture" title="ECMP Example"> <name>ECMP Example</name>
<artwork align="left"><![CDATA[ <artwork align="left" name="" type="" alt=""><![CDATA[
--L1----- --L1-----
BFR1 --L2----- BFR2 BFR1 --L2----- BFR2
--L3----- --L3-----
BIFT entry in BFR1: BIFT entry in BFR1:
------------------------------------------------------------------ ------------------------------------------------------------------
| Index | Adjacencies | | Index | Adjacencies |
================================================================== ==================================================================
| 0:6 | ECMP({forward_connected(L1, BFR2), | | 0:6 | ECMP({forward_connected(L1, BFR2), |
| | forward_connected(L2, BFR2), | | | forward_connected(L2, BFR2), |
skipping to change at line 1313 skipping to change at line 1108
------------------------------------------------------------------ ------------------------------------------------------------------
BIFT entry in BFR2: BIFT entry in BFR2:
------------------------------------------------------------------ ------------------------------------------------------------------
| Index | Adjacencies | | Index | Adjacencies |
================================================================== ==================================================================
| 0:6 | ECMP({forward_connected(L1, BFR1), | | 0:6 | ECMP({forward_connected(L1, BFR1), |
| | forward_connected(L2, BFR1), | | | forward_connected(L2, BFR1), |
| | forward_connected(L3, BFR1)}, seed) | | | forward_connected(L3, BFR1)}, seed) |
------------------------------------------------------------------ ------------------------------------------------------------------
]]></artwork></figure> ]]></artwork>
</figure>
<t>This document does not standardize any ECMP algorithm because it <t>This document does not standardize any ECMP algorithm because it
is sufficient for implementations to document their freely chosen is sufficient for implementations to document their freely chosen
ECMP algorithm. ECMP algorithm.
<xref target="ecmp-algo-picture"/> shows an example ECMP algorithm, <xref target="ecmp-algo-picture" format="default"/> shows an example ECMP algori
and would double as its documentation: A BIER-TE controller could thm
and would double as its documentation: a BIER-TE controller could
determine which adjacency is chosen based on the seed and adjacencies parameters determine which adjacency is chosen based on the seed and adjacencies parameters
and the packet entropy.</t> and on packet entropy.</t>
<figure anchor="ecmp-algo-picture">
<figure anchor="ecmp-algo-picture" title="ECMP algorithm Example"> <name>ECMP Algorithm Example</name>
<artwork align="left"><![CDATA[ <artwork align="left" name="" type="" alt=""><![CDATA[
forward(packet, ECMP(adj(0), adj(1),... adj(N-1), seed)): forward(packet, ECMP(adj(0), adj(1),... adj(N-1), seed)):
i = (packet(bier-header-entropy) XOR seed) % N i = (packet(bier-header-entropy) XOR seed) % N
forward packet to adj(i) forward packet to adj(i)
]]></artwork>
]]></artwork></figure> </figure>
<t>In the example shown in <xref target="polarization-picture"/>, all
<t>In the following example, all traffic from BFR1 towards BFR10 is traffic from BFR1 towards BFR10 is
intended to be ECMP load split equally across the topology. This intended to be ECMP load-split equally across the topology. This
example is not meant as a likely setup, but to illustrate that ECMP can example is not meant as a likely setup; rather, it illustrates that ECMP can
be used to share BPs not only across link bundles, but also across be used to share BPs not only across link bundles but also across
alternative paths across different transit BFR, and it explains alternative paths across different transit BFRs, and it explains
the use of the seed parameter.</t> the use of the seed parameter.</t>
<figure anchor="polarization-picture">
<figure anchor="polarization-picture" title="Polarization Example"> <name>Polarization Example</name>
<artwork align="left"><![CDATA[ <artwork align="left" name="" type="" alt=""><![CDATA[
BFR1 (BFIR) BFR1 (BFIR)
/L11 \L12 /L11 \L12
/ \ / \
BFR2 BFR3 BFR2 BFR3
/L21 \L22 /L31 \L32 /L21 \L22 /L31 \L32
/ \ / \ / \ / \
BFR4 BFR5 BFR6 BFR7 BFR4 BFR5 BFR6 BFR7
\ / \ / \ / \ /
\ / \ / \ / \ /
BFR8 BFR9 BFR8 BFR9
skipping to change at line 1387 skipping to change at line 1180
BIFT entry in BFR6, BFR7: BIFT entry in BFR6, BFR7:
------------------------------------------------------------------ ------------------------------------------------------------------
| 0:8 | forward_connected(Lxx, BFR9) |xx differs on BFR6/BFR7| | 0:8 | forward_connected(Lxx, BFR9) |xx differs on BFR6/BFR7|
------------------------------------------------------------------ ------------------------------------------------------------------
BIFT entry in BFR8, BFR9: BIFT entry in BFR8, BFR9:
------------------------------------------------------------------ ------------------------------------------------------------------
| 0:9 | forward_connected(Lxx, BFR10) |xx differs on BFR8/BFR9| | 0:9 | forward_connected(Lxx, BFR10) |xx differs on BFR8/BFR9|
------------------------------------------------------------------ ------------------------------------------------------------------
]]></artwork>
]]></artwork></figure> </figure>
<t>Note that for the following discussion of ECMP, only the BIFT ECMP(
<t>Note that for the following discussion of ECMP, only the BIFT ECMP )
adjacencies on BFR1, BFR2, BFR3 are relevant. The re-use of BP across adjacencies on BFR1, BFR2, and BFR3 are relevant. The reuse of BPs across
BFR in this example is further explained in <xref target="reuse"/> BFRs in this example is further explained in <xref target="reuse" format="defaul
t"/>
below.</t> below.</t>
<t> With the ECMP setup shown in the topology above, traffic would not
<t> With the setup of ECMP in the topology above, traffic would not be be
equally load-split. Instead, links L22 and L31 would see no traffic equally load-split. Instead, links L22 and L31 would see no traffic
at all: BFR2 will only see traffic from BFR1 for which the ECMP at all: BFR2 will only see traffic from BFR1, for which the ECMP
hash in BFR1 selected the first adjacency in the list of 2 adjacencies hash in BFR1 selected the first adjacency in the list of two adjacencies
given as parameters to the ECMP. It is link L11-to-BFR2. BFR2 performs given as parameters to the ECMP: link L11-to-BFR2. BFR2 again performs
again ECMP with two adjacencies on that subset of traffic using the same ECMP with two adjacencies on that subset of traffic using the same
seed1, and will therefore again select the first of its two adjacencies: seed1 and will therefore again select the first of its two adjacencies:
L21-to-BFR4. And therefore L22 and BFR5 sees no traffic. Likewise for L21-to-BFR4. Therefore, L22 and BFR5 see no traffic (likewise for
L31 and BFR6.</t> L31 and BFR6).</t>
<t>This issue in BFR2/BFR3 is called "polarization". It results from t
<t>This issue in BFR2/BFR3 is called polarization. It results from the he
re-use of the same hash function across multiple consecutive hops in reuse of the same hash function across multiple consecutive hops in
topologies like these. To resolve this issue, the ECMP() adjacency on BFR1 topologies like these. To resolve this issue, the ECMP() adjacency on BFR1
can be set up with a different seed2 than the ECMP() adjacencies on BFR2/BFR3. can be set up with a different seed2 than the ECMP() adjacencies on BFR2/BFR3.
BFR2/BFR3 can use the same hash because packets will not sequentially BFR2/BFR3 can use the same hash because packets will not sequentially
pass across both of them. Therefore, they can also use the same BP 0:7.</t> pass across both of them. Therefore, they can also use the same BP (i.e., 0:7).<
/t>
<t>Note that ECMP solutions outside of BIER often hide the <t>Note that ECMP solutions outside of BIER often hide the
seed by auto-selecting it from local entropy such as unique local or seed by auto-selecting it from local entropy such as unique local or
next-hop identifiers. Allowing the BIER-TE Controller to explicitly set the seed next-hop identifiers. Allowing the BIER-TE controller to explicitly set the seed
gives gives
the ability for it to control same/different path selection across multiple the BIER-TE controller the ability to control the selection of the same path or
different paths across multiple
consecutive ECMP hops.</t> consecutive ECMP hops.</t>
</section>
</section> <section anchor="routed" numbered="true" toc="default">
<!-- ecmp --> <name>Forward Routed Adjacencies</name>
<section anchor="routed" title="Forward Routed adjacencies"> <section anchor="reducing" numbered="true" toc="default">
<name>Reducing Bit Positions</name>
<section anchor="reducing" title="Reducing bit positions"> <t>Forward_routed() adjacencies can reduce the number of bit positio
ns
<t>Forward_routed() adjacencies can reduce the number of bit positions
required when the path steering requirement is not hop-by-hop required when the path steering requirement is not hop-by-hop
explicit path selection, but loose-hop selection. Forward_routed() adjacencies explicit path selection but rather is loose-hop selection. Forward_routed() adja
can also allow to operate BIER-TE across intermediate hop routers cencies
can also permit BIER-TE operation across intermediate-hop routers
that do not support BIER-TE.</t> that do not support BIER-TE.</t>
<t>Assume that the requirement in <xref target="routed-picture" form
at="default"/> is to explicitly steer
traffic flows that have arrived at BFR1 or BFR4 via a path
in the routing underlay "Network Area 1" to one of the following next three
segments: (1) BFR2 via link L1, (2) BFR2 via link L2, or (3) via BFR3 and then
not caring whether the packet is forwarded via L3 or L4.</t>
<figure anchor="routed-picture" title="Forward Routed Adjacencies Example"> <figure anchor="routed-picture">
<artwork align="left"><![CDATA[ <name>Forward Routed Adjacencies Example</name>
<artwork align="left" name="" type="" alt=""><![CDATA[
............... ...............
...BFR1--... ...--L1-- BFR2... ...BFR1--... ...--L1-- BFR2...
... .Routers. ...--L2--/ ... .Routers. ...--L2--/
...BFR4--... ...--L3-- BFR3... ...BFR4--... ...--L3-- BFR3...
... ...--L4--/ | ... ...--L4--/ |
............... | ............... |
LO LO
Network Area 1 Network Area 1
]]></artwork></figure> ]]></artwork>
</figure>
<t>Assume the requirement in <xref target="routed-picture"/> is to explicitly st
eer
traffic flows that have arrived at BFR1 or BFR4 via a path
in the routing underlay "Network Area 1" to one of the following three next
segments: (1) BFR2 via link L1, (2) BFR2 via link L2, or (3) via BFR3 and then
nor caring whether the packet is forwarded via L3 or L4.</t>
<t>To enable this, both BFR1 and BFR4 are set up with a forward_routed <t>To enable this, both BFR1 and BFR4 are set up with a forward_rout ed()
adjacency bit position towards an address of BFR2 on link L1, another adjacency bit position towards an address of BFR2 on link L1, another
forward_routed() bit position towards an address of BFR2 on link L2 and a third forward_routed() bit position towards an address of BFR2 on link L2, and a third
forward_routed() bit position towards a node address LO of BFR3.</t> forward_routed() bit position towards a node address LO of BFR3.</t>
</section>
</section> <section anchor="without" numbered="true" toc="default">
<!-- reducing --> <name>Supporting Nodes without BIER-TE</name>
<t>Forward_routed() adjacencies also enable incremental deployment o
<section anchor="without" title="Supporting nodes without BIER-TE"> f BIER-TE.
Only the nodes through which BIER-TE traffic needs to be steered --
<t>Forward_routed() adjacencies also enable incremental deployment of BIER-TE. with or without replication -- need to support BIER-TE. Where
Only the nodes through which BIER-TE traffic needs to be steered - they are not directly connected to each other, forward_routed()
with or without replication - need to support BIER-TE. Where adjacencies are used to pass over nodes that are not BIER-TE enabled.</t>
they are not directly connected to each other, forward_routed </section>
adjacencies are used to pass over non BIER-TE enabled nodes.</t>
</section>
<!-- without -->
</section> </section>
<!-- routed -->
<section anchor="reuse" title="Reuse of bit positions (without DNC)">
<t>Bit positions can be re-used across multiple BFRs to minimize the number <section anchor="reuse" numbered="true" toc="default">
of BP needed. This happens when adjacencies on multiple BFRs use the DNC <name>Reuse of Bit Positions (without DNC)</name>
<t>BPs can be reused across multiple BFRs to minimize the number
of BPs needed. This happens when adjacencies on multiple BFRs use the DNC
flag as described above, but it can also be done for non-DNC adjacencies. flag as described above, but it can also be done for non-DNC adjacencies.
This section only discusses this non-DNC case.</t> This section only discusses this non-DNC case.</t>
<t>Because a given BP is cleared when passing a BFR with an adjacency
<t>Because BP are cleared when passing a BFR with an adjacency for that for that
BP, reuse of BP across multiple BFRs does not introduce any problems BP, reusing BPs across multiple BFRs does not introduce any problems
with duplicates or loops that do not also exist when every adjacency has with duplicates or loops that do not also exist when every adjacency has
a unique BP. Instead, the challenge when reusing BP is whether it a unique BP. Instead, the challenge when reusing BPs is whether the desired
allows to still achieve the desired Tree Engineering goals.</t> Tree Engineering goals can still be achieved.</t>
<t>A BP cannot be reused across two BFRs that would need to be passed
<t>BP cannot be reused across two BFRs that would need to be passed sequentially for some path: the first BFR will clear the BP, so those
sequentially for some path: The first BFR will clear the BP, so those paths cannot be built. A BP can be set across BFRs that would only occur across
paths cannot be built. BP can be set across BFR that would (A) only (A) different paths or (B) different branches of the same tree.</t>
occur across different paths or (B) across different branches of the same tree.< <t>An example of (A) was given in <xref target="polarization-picture"
/t> format="default"/>,
where BP 0:7, BP 0:8, and BP 0:9 are each reused across multiple BFRs because
<t>An example of (A) was given in <xref target="polarization-picture"/>,
where BP 0:7, BP 0:8 and BP 0:9 are each reused across multiple BFRs because
a single packet/path would never be able to reach more than one BFR a single packet/path would never be able to reach more than one BFR
sharing the same BP.</t> sharing the same BP.</t>
<t>Assume that the example was changed: BFR1 has no ECMP() adjacency f
<t>Assume the example was changed: BFR1 has no ECMP() adjacency for BP 0:6, or BP 0:6
but instead BP 0:5 with forward_connected() to BFR2 and BP 0:6 with but instead has BP 0:5 with forward_connected() to BFR2 and BP 0:6 with
forward_connected() to BFR3. Packets with both BP 0:5 and BP 0:6 would forward_connected() to BFR3. Packets with both BP 0:5 and BP 0:6 would
now be able to reach both BFR2 and BFR3 and the still existing re-use now be able to reach both BFR2 and BFR3, and the still-existing reuse
of BP 0:7 between BFR2 and BFR3 is a case of (B) where reuse of BP of BP 0:7 between BFR2 and BFR3 is a case of (B) where reusing a BP
is perfect because it does not limit the set of useful path choices:</t> is perfect because it does not limit the set of useful path choices, as in the f
ollowing example.</t>
<t>If instead of reusing BP 0:7, BFR3 used a separate BP 0:10 for its <t>If instead of reusing BP 0:7 BFR3 used a separate BP 0:10 for its
ECMP() adjacency, no useful additional path steering options would be enabled. ECMP() adjacency, no useful additional path steering options would be enabled.
If duplicates at BFR10 where undesirable, this would be done by not If duplicates at BFR10 were undesirable, this would be done by not
setting BP 0:5 and BP 0:6 for the same packet. If the duplicates where setting BP 0:5 and BP 0:6 for the same packet. If the duplicates were
desirable (e.g.: resilient transmission), the additional BP 0:10 desirable (e.g., resilient transmission), the additional BP 0:10
would also not render additional value.</t> would also not render additional value.</t>
<t>Reuse may also save BPs in larger topologies. Consider the topolog
y
shown in <xref target="scaling-picture2" format="default"/>.</t>
<figure anchor="scaling-picture2" title="Reuse of BP"> <figure anchor="scaling-picture2">
<artwork align="left"><![CDATA[ <name>Reuse of BPs</name>
<artwork align="left" name="" type="" alt=""><![CDATA[
area1 area1
BFR1a BFR1b BFR1a BFR1b
/ \ / \
.................................... ....................................
. Core . . Core .
.................................... ....................................
| / \ / \ | | / \ / \ |
BFR2a BFR2b BFR3a BFR3b BFR6a BFR6b BFR2a BFR2b BFR3a BFR3b BFR6a BFR6b
/-------\ /---------\ /--------\ /-------\ /---------\ /--------\
| area2 | | area3 | ... | area6 | | area2 | | area3 | ... | area6 |
| ring | | ring | | ring | | ring | | ring | | ring |
\-------/ \---------/ \--------/ \-------/ \---------/ \--------/
more BFR more BFR more BFR more BFRs more BFRs more BFRs
]]></artwork></figure> ]]></artwork>
</figure>
<t>Reuse may also save BPs in larger topologies. Consider the topology <t>A BFIR/sender (e.g., video headend) is attached to area 1,
shown in <xref target="scaling-picture2"/>. A BFIR/sender (e.g.: video headend) and the five areas 2...6 contain receivers/BFERs. Assume that each area has a di
is attached to area 1, stribution
and area 2...6 contain receivers/BFER. Assume each area had a distribution
ring, each with two BPs to indicate the direction (as explained before). ring, each with two BPs to indicate the direction (as explained before).
These two BPs could be reused across the 5 areas. Packets would be replicated These two BPs could be reused across the five areas. Packets would be replicate
through other BPs for the Core to the desired subset of areas, and once a packet d
copy through other BPs from the core to the desired subset of areas, and once a packe
t copy
reaches the ring of the area, the two ring BPs come into play. This reuse is reaches the ring of the area, the two ring BPs come into play. This reuse is
a case of (B), but it limits the topology choices: Packets a case of (B), but it limits the topology choices: packets
can only flow around the same direction in the rings of all areas. This may or m ay not can only flow around the same direction in the rings of all areas. This may or m ay not
be acceptable based on the desired path steering options: If resilient be acceptable based on the desired path steering options: if resilient
transmission is the path engineering goal, then it is likely a good transmission is the path engineering goal, then it is likely a good
optimization, if the bandwidth of each ring was to be optimized separately, optimization; however, if the bandwidth of each ring were to be optimized separa tely,
it would not be a good limitation.</t> it would not be a good limitation.</t>
</section>
</section> <section anchor="bits-summary" numbered="true" toc="default">
<section anchor="bits-summary" title="Summary of BP optimizations"> <name>Summary of BP Optimizations</name>
<t>In this section, we reviewed a range of techniques by which a BIER-
<t>This section reviewed a range of techniques by which a BIER-TE Controller can TE controller can create
create
a BIER-TE topology in a way that minimizes the number of necessary BPs.</t> a BIER-TE topology in a way that minimizes the number of necessary BPs.</t>
<t>Without any optimization, a BIER-TE controller would attempt to map
<t>Without any optimization, a BIER-TE Controller would attempt to map the netwo the network
rk subnet topology 1:1 into the BIER-TE topology, every adjacent
subnet topology 1:1 into the BIER-TE topology and every subnet adjacent neighbor in the subnet would require a forward_connected() BP, and every BFER wo
neighbor requires a forward_connected() BP and every BFER requires a local_decap uld require a local_decap() BP.</t>
() BP.</t> <t>The optimizations described in this document are then as follows:</
t>
<t>The optimizations described are then as follows:<list style="symbols"> <ol spacing="normal">
<t>P2P links require only one BP (<xref target="p2p-links"/>).</t> <li>P2P links require only one BP (<xref target="p2p-links" format="
<t>All leaf-BFER can share a single local_decap() BP (<xref target="leaf-bfer" default"/>).</li>
/>).</t> <li>All leaf BFERs can share a single local_decap() BP (<xref target
<t>A LAN with N BFR needs at most N BP (one for each BFR). It only needs one B ="leaf-bfer" format="default"/>).</li>
P for all those BFR that are not redundantly connected to multiple LANs (<xref t <li>A LAN with N BFRs needs at most N BPs (one for each BFR). It onl
arget="lans"/>).</t> y needs one BP for all those BFRs that are not redundantly connected to multiple
<t>A hub with p2p connections to multiple non-leaf-BFER spokes can share one B LANs (<xref target="lans" format="default"/>).</li>
P to all spokes if traffic can be flooded to all spokes, e.g.: because of no ban <li>A hub with P2P connections to multiple non-leaf BFER spokes can
dwidth concerns or dense receiver sets (<xref target="hubnspoke"/>).</t> share one BP with all of the spokes if traffic can be flooded to all of those sp
<t>Rings of BFR can be built with just two BP (one for each direction) except okes, e.g., because of no bandwidth concerns or dense receiver sets (<xref targe
for BFR with multiple ring connections - similar to LANs (<xref target="rings"/> t="hubnspoke" format="default"/>).</li>
).</t> <li>Rings of BFRs can be built with just two BPs (one for each direc
<t>ECMP() adjacencies to N neighbors can replace N BP with 1 BP. Multihop ECMP tion), except for BFRs with multiple ring connections -- similar to LANs (<xref
can avoid polarization through different seeds of the ECMP algorithm (<xref tar target="rings" format="default"/>).</li>
get="ecmp"/>).</t> <li>ECMP() adjacencies to N neighbors can replace N BPs with one BP.
<t>Forward_routed() adjacencies allow to "tunnel" across non-BIER-TE capable r Multihop ECMP can avoid polarization through different seeds of the ECMP algori
outers and across BIER-TE capable routers where no traffic-steering or replicati thm (<xref target="ecmp" format="default"/>).</li>
ons are required (<xref target="routed"/>).</t> <li>Forward_routed() adjacencies permit "tunneling" across routers t
<t>BP can generally be reused across a set of nodes where it can be guaranteed hat are either BIER-TE capable or not BIER-TE capable where no traffic steering
that no path will or replications are required (<xref target="routed" format="default"/>).</li>
ever need to traverse more than one node of the set. Depending on scenario, this <li>A BP can generally be reused across a set of nodes where it can
may limit the feasible path steering options (<xref target="reuse"/>).</t> be guaranteed that no path will
ever need to traverse more than one node of the set. Depending on the scenario,
</list></t> this may limit the feasible path steering options (<xref target="reuse" format="
default"/>).</li>
<t>Note that the described list of optimizations is not exhaustive. Especially w </ol>
hen the set of required path steering choices is limited and the set of possible <t>Note that this list of optimizations is not exhaustive. Further opt
subsets of BFERs that should be able to receive traffic is limited, further opt imizations of BPs are possible, especially when both the set of required path st
imizations of BP are possible. The hub and spoke optimization is a simple exampl eering choices and the possible subsets of BFERs that should be able to receive
e of such traffic pattern dependent optimizations.</t> traffic are limited. The hub-and-spoke optimization is a simple example of such
traffic-pattern-dependent optimizations.</t>
</section>
</section> </section>
</section> <section anchor="avoiding" numbered="true" toc="default">
<!-- bitpositions --> <name>Avoiding Duplicates and Loops</name>
<section anchor="loops" numbered="true" toc="default">
<section anchor="avoiding" title="Avoiding duplicates and loops"> <name>Loops</name>
<t>Whenever BIER-TE creates a copy of a packet, the BitString of
<section anchor="loops" title="Loops">
<t>Whenever BIER-TE creates a copy of a packet, the BitString of
that copy will have all bit positions cleared that are associated that copy will have all bit positions cleared that are associated
with adjacencies on the BFR. This inhibits looping of packets. with adjacencies on the BFR. This prevents packets from looping.
The only exception are adjacencies with DNC set.</t> The only exceptions are adjacencies with DNC set.</t>
<figure anchor="ring-picture2" title="Miswired Ring Example"> <t>With DNC set, looping can happen. Consider in <xref target="ring-p
<artwork align="left"><![CDATA[ icture2" format="default"/>
that link L4 from BFR3 is (inadvertently) plugged into the L1 interface of
BFRa (instead of BFR2). This creates a loop where the ring's clockwise bit posit
ion is
never cleared for copies of the packets traveling clockwise
around the ring.</t>
<figure anchor="ring-picture2">
<name>Miswired Ring Example</name>
<artwork align="left" name="" type="" alt=""><![CDATA[
v v v v
| | | |
L1 | L2 | L3 L1 | L2 | L3
/-------- BFRa ---- BFRb ---------------------\ /-------- BFRa ---- BFRb ---------------------\
| . | | . |
| ...... Wrong link wiring | | ...... Wrong link wiring |
| . | | . |
\- BFR1 - BFR2 BFR3 - ... - BFR29 - BFR30 -/ \- BFR1 - BFR2 BFR3 - ... - BFR29 - BFR30 -/
| | L4 | | | | L4 | |
p33| p15| p33| p15|
BFRd BFRc BFRd BFRc
]]></artwork></figure> ]]></artwork>
</figure>
<t>With DNC set, looping can happen. Consider in <xref target="ring-picture2"/> <t>To inhibit looping in the face of such physical misconfiguration,
that link L4 from BFR3 is (inadvertently) plugged into the L1 interface of
BFRa (instead of BFR2). This creates a loop where the rings clockwise bit positi
on is
never cleared for copies of the packets traveling clockwise
around the ring.</t>
<t>To inhibit looping in the face of such physical misconfiguration,
only forward_connected() adjacencies are permitted to have DNC set, only forward_connected() adjacencies are permitted to have DNC set,
and the link layer port unique unicast destination address of the adjacency (e.g . MAC address) and the link layer port unique unicast destination address of the adjacency (e.g ., "Media Access Control" (MAC) address)
protects against closing the loop. Link layers without port unique protects against closing the loop. Link layers without port unique
link layer addresses should not be used with the DNC flag set.</t> link layer addresses should not be used with the DNC flag set.</t>
</section>
</section> <section anchor="duplicates" numbered="true" toc="default">
<!-- loops --> <name>Duplicates</name>
<section anchor="duplicates" title="Duplicates">
<figure anchor="duplicates-picture" title="Duplicates Example"> <t>Duplicates happen when the graph expressed by a BitString is not a
<artwork align="left"><![CDATA[ tree but is redundantly connecting BFRs with each other. In <xref target="duplic
ates-picture" format="default"/>,
a BitString of p2,p3,p4,p5 would result in duplicate packets arriving on BFER4.
The BIER-TE controller must therefore ensure that only BitStrings that are trees
are created.</t>
<figure anchor="duplicates-picture">
<name>Duplicates Example</name>
<artwork align="left" name="" type="" alt=""><![CDATA[
BFIR1 BFIR1
/ \ / \
/ p2 \ p3 / p2 \ p3
BFR2 BFR3 BFR2 BFR3
\ p4 / p5 \ p4 / p5
\ / \ /
BFER4 BFER4
]]></artwork></figure> ]]></artwork>
</figure>
<t>Duplicates happen when the graph expressed by a BitString is not a <t>When links are incorrectly physically reconnected before the
tree but redundantly connecting BFRs with each other. In <xref target="duplicate BIER-TE controller updates BitStrings in BFIRs, duplicates can happen.
s-picture"/>,
a BitString of p2,p3,p4,p5 would result in duplicate packets to arrive on BFER4.
The BIER-TE Controller must therefore ensure to only create BitStrings that are
trees.</t>
<t>When links are incorrectly physically re-connected before the
BIER-TE Controller updates BitStrings in BFIRs, duplicates can happen.
Like loops, these can be inhibited by link layer addressing Like loops, these can be inhibited by link layer addressing
in forward_connected() adjacencies.</t> in forward_connected() adjacencies.</t>
<t>If interface or loopback addresses used in forward_routed() adjacen
<t>If interface or loopback addresses used in forward_routed() adjacencies cies
are moved from one BFR to another, duplicates can equally happen. are moved from one BFR to another, duplicates are equally likely to happen.
Such re-addressing operations must be coordinated with the BIER-TE Controller.</ Such readdressing operations must be coordinated with the BIER-TE controller.</t
t> >
</section>
</section>
<!-- duplicates -->
</section> </section>
<!-- avoiding -->
<section anchor="mgmt-stuff" title="Managing SI, sub-domains and BFR-ids"> <section anchor="mgmt-stuff" numbered="true" toc="default">
<name>Managing SIs, Subdomains, and BFR-ids</name>
<t>When the number of bits required to represent the necessary hops <t>When the number of bits required to represent the necessary hops
in the topology and BFER exceeds the supported BitStringLength (BSL), in the topology and BFERs exceeds the supported "BitStringLength" (BSL),
multiple SIs and/or sub-domains must be used. This section discusses how.</t> multiple SIs and/or subdomains must be used. This section discusses how this is
done.</t>
<t>BIER-TE forwarding does not require the concept of BFR-id, but routing <t>BIER-TE forwarding does not require the concept of BFR-ids, but routi
underlay, flow overlay and BIER headers may. This section also discusses ng
how BFR-ids can be assigned to BFIR/BFER for BIER-TE.</t> underlay, flow overlay, and BIER headers may. This section also discusses
how BFR-ids can be assigned to BFIRs/BFERs for BIER-TE.</t>
<section anchor="why" title="Why SI and sub-domains"> <section anchor="why" numbered="true" toc="default">
<name>Why SIs and Subdomains?</name>
<t>For (non-TE) BIER and BIER-TE forwarding, the most important result of using <t>For (non-TE) BIER and BIER-TE forwarding, the most important result
multiple of using multiple
SI and/or sub-domains is the same: Packets that need to be sent to BFERs in SIs and/or subdomains is the same: multicast flow overlay packets that need to b
different SIs or sub-domains require different BIER packets: each one with a e sent to BFERs in
BitString for a different (SI,sub-domain) combination. Each such BitString uses different SIs or subdomains require multiple BIER packets, each one with a
one BSL sized SI block in the BIFT of the sub-domain. We call this BitString for a different (SI,subdomain) combination. Each such BitString uses
one BSL-sized SI block in the BIFT of the subdomain. We call this
a BIFT:SI (block).</t> a BIFT:SI (block).</t>
<t>SIs and subdomains have different purposes in the BIER architecture
<t>For BIER and BIER-TE forwarding themselves there is also no difference whethe and also the BIER-TE architecture. This impacts how operators manage them and
r especially how flow overlays will likely use them.</t>
different SIs and/or sub-domains are chosen, but SI and sub-domain have <t>By default, every possible BFIR/BFER in a BIER network would likely
different purposes in the BIER architecture shared by BIER-TE. be given
This impacts how operators are managing them and how especially flow overlays a BFR-id in subdomain 0 (unless there are &gt; 64k BFIRs/BFERs). </t>
will likely use them.</t> <t>If there are different flow services (or service instances) requiri
ng replication
<t>By default, every possible BFIR/BFER in a BIER network would likely be given
a BFR-id in sub-domain 0 (unless there are > 64k BFIR/BFER). </t>
<t>If there are different flow services (or service instances) requiring replica
tion
to different subsets of BFERs, then it will likely not be possible to achieve to different subsets of BFERs, then it will likely not be possible to achieve
the best replication efficiency for all of these service instances via sub-domai the best replication efficiency for all of these service instances via subdomain
n 0. 0.
Ideal replication efficiency for N BFER exists in a sub-domain if they are
split over not more than ceiling(N/BitStringLength) SI.</t>
<t>If service instances justify additional BIER:SI state in the network, additio Ideal replication efficiency for N BFERs exists in a subdomain if they are
nal split over no more than ceiling(N/BitStringLength) SIs.</t>
sub-domains will be used: BFIR/BFER are assigned BFR-id in those sub-domains <t>If service instances justify additional BIER:SI state in the networ
and each service instance is configured to use the most appropriate sub-domain. k, additional
subdomains will be used: BFIRs/BFERs are assigned BFR-ids in those subdomains,
and each service instance is configured to use the most appropriate subdomain.
This results in improved replication efficiency for different services.</t> This results in improved replication efficiency for different services.</t>
<t>Even if creation of subdomains and assignment of BFR-ids to BFIRs/B
FERs in those
subdomains is automated, it is not expected that individual
service instances can deal with BFERs in different subdomains. A service
instance may only support configuration of a single subdomain it should rely on.
</t>
<t>To be able to easily reuse (and modify as little as possible) exist
ing
BIER procedures (including flow overlay and routing underlay), when BIER-TE
forwarding is added, we therefore reuse SIs and subdomains logically in the
same way as they are used in BIER: all necessary BFIRs/BFERs for a service use
a single BIER-TE BIFT and are split across as many SIs as necessary (see <xref t
arget="bit-requirements" format="default"/>).
Different services may use different subdomains that primarily exist to
provide more efficient replication (and, for BIER-TE, desirable path steering)
for different subsets of BFIRs/BFERs.</t>
</section>
<t>Even if creation of sub-domains and assignment of BFR-id to BFIR/BFER in thos <section anchor="bit-requirements" numbered="true" toc="default">
e <name>Assigning Bits for the BIER-TE Topology</name>
sub-domains is automated, it is not expected that individual <t>In BIER, BitStrings only need to carry bits for BFERs; this leads t
service instances can deal with BFER in different sub-domains. A service o the
instance may only support configuration of a single sub-domain it should rely on model where BFR-ids map 1:1 to each bit in a BitString.</t>
.</t> <t>In BIER-TE, BitStrings need to carry bits to indicate not only the
receiving
<t>To be able to easily reuse (and modify as little as possible) existing
BIER procedures including flow-overlay and routing underlay, when BIER-TE
forwarding is added, we therefore reuse SI and sub-domain logically in the
same way as they are used in BIER: All necessary BFIR/BFER for a service use
a single BIER-TE BIFT and are split across as many SIs as necessary (see <xref t
arget="bit-requirements"/>).
Different services may use different sub-domains that primarily exist to
provide more efficient replication (and for BIER-TE desirable path steering)
for different subsets of BFIR/BFER.</t>
</section>
<!-- why -->
<section anchor="bit-requirements" title="Assigning bits for the BIER-TE top
ology">
<t>In BIER, BitStrings only need to carry bits for BFERs, which leads to the
model that BFR-ids map 1:1 to each bit in a BitString.</t>
<t>In BIER-TE, BitStrings need to carry bits to indicate not only the receiving
BFER but also the intermediate hops/links across which the packet must be sent. BFER but also the intermediate hops/links across which the packet must be sent.
The maximum number of BFER that can be supported in a single BitString or BIFT:S I The maximum number of BFERs that can be supported in a single BitString or BIFT: SI
depends on the number of bits necessary to represent the desired topology betwee n depends on the number of bits necessary to represent the desired topology betwee n
them.</t> them.</t>
<t>"Desired" topology means that it depends on the physical topology a
<t>"Desired" topology because it depends on the physical topology, and nd
on the desire of the operator to allow for explicit path steering across the operator's desire to</t>
every single hop (which requires more bits), or reducing the number of required <ol spacing="normal">
bits by exploiting optimizations such as unicast (forward_routed()), ECMP() or f <li>permit explicit path steering across
lood every single hop (which requires more bits), or</li>
(DNC) over "uninteresting" sub-parts of the topology - e.g. parts where differen <li>reduce the number of required
t bits by exploiting optimizations such as unicast (forward_routed()), ECMP(), or
trees do not need to take different paths due to path steering reasons.</t> flood
(DNC) over "uninteresting" sub-parts of the topology, e.g., parts where, for pat
<t>The total number of bits to describe the topology vs. the number of BFERs in h steering reasons, different trees do not need to take different paths.</li>
a BIFT:SI can </ol>
<t>The total number of bits to describe the topology vs. the number of
BFERs in a BIFT:SI can
range widely based on the size of the topology and the amount of alternative pat hs range widely based on the size of the topology and the amount of alternative pat hs
in it. In a BIER-TE topology crafted by a BIER-TE expert, the higher the percent in it. In a BIER-TE topology crafted by a BIER-TE expert, the higher the percent
age of non-BFER bits, the higher the likelihood, that those topology age of non-BFER bits, the higher the likelihood that those topology
bits are not just BIER-TE overhead without additional benefit, but instead that bits are not just BIER-TE overhead without additional benefit but instead
they will allow the expression of desirable path steering alternatives.</t>
will allow to express desirable path steering alternatives.</t> </section>
<section anchor="bfr-id" numbered="true" toc="default">
</section> <name>Assigning BFR-ids with BIER-TE</name>
<t>BIER-TE forwarding does not use BFR-ids, nor does it require that
<section anchor="bfr-id" title="Assigning BFR-id with BIER-TE"> the BFIR-id field of the BIER header be set to a particular value.
However, other parts of a BIER-TE deployment may need a BFR-id -- specifically,
<t>BIER-TE forwarding does not use the BFR-id, nor does it require for multicast flow overlay signaling and multicast flow overlay packet disposition;
the BFIR-id field of the BIER header to be set to a particular value. in that case, BFRs need to also have BFR-ids for BIER-TE SDs.</t>
However, other parts of a BIER-TE deployment may need a BFR-id, specifically <t>For example, for BIER overlay signaling, BFIRs need to have a BFR-i
multicast flow overlay signaling and multicast flow overlay packet disposition, d, because this
and in that case BFRs need to also have BFR-ids for BIER-TE SDs.</t>
<t>For example, for BIER overlay signaling, BFIRs need to have a BFR-id, because
this
BFIR BFR-id is carried in the BFIR-id field of the BIER header to indicate BFIR BFR-id is carried in the BFIR-id field of the BIER header to indicate
to the overlay signaling on the receiving BFER which BFIR originated the packet. </t> to the overlay signaling on the receiving BFER which BFIR originated the packet. </t>
<t>In BIER, BFR-id = SI * BSL + BP, such that the SI and BP of a BFER
<t>In BIER, BFR-id = SI * BSL + BP, such that the SI and BP of a BFER
can be calculated from the BFR-id and vice versa. This also means can be calculated from the BFR-id and vice versa. This also means
that every BFR with a BFR-id has a reserved BP in an SI, even if that every BFR with a BFR-id has a reserved BP in an SI, even if
that is not necessary for BIER forwarding, because the BFR may that is not necessary for BIER forwarding, because the BFR may
never be a BFER but only a BFIR.</t> never be a BFER (i.e., will only be a BFIR).</t>
<t>In BIER-TE, for a non-leaf BFER, there is usually a single BP for t
<t>In BIER-TE, for a non-leaf BFER, there is usually a single BP for that BFER w hat BFER with a
ith a
local_decap() adjacency on the BFER. The BFR-id for such a BFER can therefore local_decap() adjacency on the BFER. The BFR-id for such a BFER can therefore
be determined using the same procedure as in (non-TE) BIER: BFR-id = SI * BSL + be determined using the same procedure as that used for (non-TE) BIER: BFR-id =
BP.</t> SI * BSL + BP.</t>
<t>As explained in <xref target="leaf-bfer" format="default"/>, leaf B
<t>As explained in <xref target="leaf-bfer"/>, leaf BFERs do not need such FERs do not need such
a unique local_decap() adjacency. Likewise, BFIRs that are not also BFERs a unique local_decap() adjacency. Likewise, BFIRs that are not also BFERs
may not have a unique local_decap() adjacency either. For all those BFIRs may not have a unique local_decap() adjacency either. For all those BFIRs
and (leaf) BFERs, the controller needs to determine unique BFR-ids that and (leaf) BFERs, the controller needs to determine unique BFR-ids that
do not collide with the BFR-ids derived from the non-leaf BFER local_decap() BPs .</t> do not collide with the BFR-ids derived from the non-leaf BFER local_decap() BPs .</t>
<t>While this document defines no requirements on how to allocate such
<t>While this document defines no requirements on how to allocate such BFR-id, BFR-ids,
a simple option is to derive it from the (SI,BP) of an adjacency that is a simple option is to derive it from the (SI,BP) of an adjacency that is
unique to the BFR in question. For a BFIR this can be the first adjacency unique to the BFR in question. For a BFIR, this can be the first adjacency that
only populated on this BFIR, for a leaf-BFER, this could be the first BP is
only populated on this BFIR; for a leaf BFER, this could be the first BP
with an adjacency towards that BFER.</t> with an adjacency towards that BFER.</t>
</section>
</section> <section anchor="bitstring-mappings" numbered="true" toc="default">
<name>Mapping from BFRs to BitStrings with BIER-TE</name>
<section anchor="bitstring-mappings" title="Mapping from BFR to BitStrings w <t>In BIER, applications of the flow overlay on a BFIR can calculate t
ith BIER-TE"> he (SI,BP) of a
<t>In BIER, applications of the flow overlay on a BFIR can calculate the (SI,BP)
of a
BFER from the BFR-id of the BFER and can therefore easily determine the BitStrin gs BFER from the BFR-id of the BFER and can therefore easily determine the BitStrin gs
for a BIER packet to a set of BFERs with known BFR-ids.</t> for a BIER packet to a set of BFERs with known BFR-ids.</t>
<t>In BIER-TE, this mapping needs to be equally supported for flow ove
<t>In BIER-TE this mapping needs to be equally supported for flow overlays. rlays.
This section outlines two core options, based on what type of Tree Engineering This section outlines two core options, based on what type of Tree Engineering
the BIER-TE controller needs to performs for a particular application.</t> the BIER-TE controller needs to perform for a particular application.</t>
<dl spacing="normal">
<t>"Independent branches": For a given flow overlay instance, the branches <dt>"Independent branches":</dt><dd>For a given flow overlay instance,
the branches
from a BFIR to every BFER are calculated by the BIER-TE controller to be from a BFIR to every BFER are calculated by the BIER-TE controller to be
independent of the branches to any other BFER. Shortest path trees are the most common independent of the branches to any other BFER. Shortest path trees are the most common
examples of trees with independent branches.</t> examples of trees with independent branches.</dd>
<dt>"Interdependent branches":</dt><dd>When a BFER is added to or dele
<t>"Interdependent branches": When a BFER is added or deleted from a particular ted from a particular
distribution tree, the BIER-TE controller has to recalculate the branches to oth distribution tree, the BIER-TE controller has to recalculate the branches to oth
er BFER, er BFERs,
because they may need to change. Steiner trees are examples of interdependent b because they may need to change. Steiner trees are examples of interdependent b
ranch trees.</t> ranch trees.</dd>
</dl>
<t>If "independent branches" are used, the BIER-TE Controller <t>If "independent branches" are used, the BIER-TE controller
can signal to the BFIR flow overlay for every BFER an SI:BitString that can signal to the BFIR flow overlay for every BFER an SI:BitString that
represents the branch to that BFER. The flow overlay on the BIFR can then indep represents the branch to that BFER. The flow overlay on the BFIR can then, inde
endently pendently
of the controller calculate the SI:BitString for all desired BFERs by OR'ing the of the controller, calculate the SI:BitString for all desired BFERs by ORing the
ir BitStrings. ir BitStrings.
This allows for flow overlay applications to operate independently of the contro This allows flow overlay applications to operate independently of the controller
ller whenever they need to determine which subset of BFERs needs to receive a particu
whenever it needs to determine which subset of BFERs need to receive a particula lar packet.</t>
r packet.</t> <t>If "interdependent branches" are required, an application would nee
d to query
<t>If "interdependent branches" are required, the application would need to inqu the SI:BitString for a given set of BFERs whenever the set changes.</t>
ire <t>Note that in either case (unlike the scenario for BIER), the bits m
the SI:BitString for a given set of BFER whenever the set changes.</t> ay need to
change upon link/node failure/recovery, network expansion, or network resource c
<t>Note that in either case (unlike in BIER), the bits may need to onsumption
change upon link/node failure/recovery, network expansion and network resource c by other traffic as part of achieving Traffic Engineering goals (e.g., reoptimiz
onsumption ation of
by other traffic as part of traffic engineering goals (e.g.: re-optimization of lower-priority traffic flows). Interactions between such BFIR applications and t
lower he BIER-TE controller
priority traffic flows). Interactions between such BFIR applications and the BIE do therefore need to support dynamic updates to the SIs:BitStrings.</t>
R-TE Controller <t>Communications between the BFIR flow overlay and the BIER-TE contro
do therefore need to support dynamic updates to the SI:BitStrings.</t> ller
require some way to identify the BFERs. If BFR-ids are used in the deployment, a
<t>Communications between the BFIR flow overlay and the BIER-TE controller s
requires some way to identify the BFER. If BFR-ids are used in the deployment, a outlined in <xref target="bfr-id" format="default"/>, then those are the "natura
s l" BFR-ids. If
outlined in <xref target="bfr-id"/>, then those are the natural BFR identifier. BFR-ids are not used, then any other unique identifier, such as a BFR's BFR-pref
If ix
BFR-ids are not used, then any other unique identifier, such as the BFR-prefix <xref target="RFC8279" format="default"/>, could be used.</t>
of the BFR (<xref target="RFC8279"/>) could be used.</t> </section>
</section>
<!-- bfr-id -->
<section anchor="assigning" title="Assigning BFR-ids for BIER-TE">
<t>It is not currently determined if a single sub-domain could or should be <section anchor="assigning" numbered="true" toc="default">
<name>Assigning BFR-ids for BIER-TE</name>
<t>It is not currently determined if a single subdomain could or shoul
d be
allowed to forward both (non-TE) BIER and BIER-TE packets. If this should be allowed to forward both (non-TE) BIER and BIER-TE packets. If this should be
supported, there are two options:</t> supported, there are two options:</t>
<ol spacing="normal" type="A">
<t>A. BIER and BIER-TE have different BFR-id in the same sub-domain. This allows <li>BIER and BIER-TE have different BFR-ids in the same subdomain. Thi
higher replication efficiency for BIER because their BFR-id can be assigned s allows higher replication efficiency for BIER because the BIER BFR-ids can be
sequentially, while the BitStrings for BIER-TE will have also the additional assigned
bits for the topology. There is no relationship between a BFR BIER BFR-id and it sequentially, while the BitStrings for BIER-TE will also have to assign the addi
s tional
BIER-TE BFR-id.</t> bits for the topology adjacencies. There is no relationship between a BFR BIER B
FR-id and its
<t>B. BIER and BIER-TE share the same BFR-id. The BFR-ids are assigned as explai BIER-TE BFR-id.</li>
ned <li>BIER and BIER-TE share the same BFR-id. The BFR-ids are assigned a
s explained
above for BIER-TE and simply reused for BIER. The replication efficiency for BIE R will above for BIER-TE and simply reused for BIER. The replication efficiency for BIE R will
be as low as that for BIER-TE in this approach.</t> be as low as that for BIER-TE in this approach.</li>
</ol>
</section> </section>
<!-- assigning -->
<section anchor="allocation-example" title="Example bit allocations">
<section anchor="with-bier" title="With BIER">
<t>Consider a network setup with a BSL of 256 for a network
topology as shown in <xref target="scaling-picture"/>. The network has 6 areas,
each with
170 BFERs, connecting via a core with 4 (core) BFRs. To address all BFERs with B
IER,
4 SIs are required. To send a BIER
packet to all BFER in the network, 4 copies need to be sent by the BFIR. On the
BFIR it does not make a difference how the BFR-ids are allocated to BFER
in the network, but for efficiency further down in the network it does
make a difference.</t>
<figure anchor="scaling-picture" title="Scaling BIER-TE bits by reuse"> <section anchor="allocation-example" numbered="true" toc="default">
<artwork align="left"><![CDATA[ <name>Example Bit Allocations</name>
<section anchor="with-bier" numbered="true" toc="default">
<name>With BIER</name>
<t>Consider a network setup with a BSL of 256 for a network
topology as shown in <xref target="scaling-picture" format="default"/>. The netw
ork has six areas, each with
170 BFERs, connecting via a core with four (core) BFRs. To address all BFERs wit
h BIER,
four SIs are required. To send a BIER
packet to all BFERs in the network, four copies need to be sent by the BFIR. On
the
BFIR, it does not matter how the BFR-ids are allocated to BFERs
in the network, but it does matter for efficiency further down in the network.</
t>
<figure anchor="scaling-picture">
<name>Scaling BIER-TE Bits by Reuse</name>
<artwork align="left" name="" type="" alt=""><![CDATA[
area1 area2 area3 area1 area2 area3
BFR1a BFR1b BFR2a BFR2b BFR3a BFR3b BFR1a BFR1b BFR2a BFR2b BFR3a BFR3b
| \ / \ / | | \ / \ / |
................................ ................................
. Core . . Core .
................................ ................................
| / \ / \ | | / \ / \ |
BFR4a BFR4b BFR5a BFR5b BFR6a BFR6b BFR4a BFR4b BFR5a BFR5b BFR6a BFR6b
area4 area5 area6 area4 area5 area6
]]></artwork></figure> ]]></artwork>
</figure>
<t>With random allocation of BFR-id to BFER, each receiving area would (most lik <t>With random allocation of BFR-ids to BFERs, each receiving area w
ely) ould (most likely)
have to receive all 4 copies of the BIER packet because there would be have to receive all four copies of the BIER packet because there would be
BFR-id for each of the 4 SIs in each of the areas. Only further towards each BFR-ids for each of the four SIs in each of the areas. Only further towards each
BFER would this duplication subside - when each of the 4 trees runs out of BFER would this duplication subside -- when each of the four trees runs out of
branches.</t> branches.</t>
<t>If BFR-ids are allocated intelligently, then all the BFERs in an
<t>If BFR-ids are allocated intelligently, then all the BFER in an area area
would be given BFR-id with as few as possible different SIs. would be given BFR-ids with as few different SIs as possible.
Each area would only have to forward one or two packets instead of 4.</t> Each area would only have to forward one or two packets instead of four.</t>
<t>Given how networks can grow over time, replication efficiency in
<t>Given how networks can grow over time, replication efficiency in an area an area
will then also go down over time when BFR-ids are only allocated sequentially, n etwork wide. will then also go down over time when BFR-ids are only allocated sequentially, n etwork wide.
An area that initially only has BFR-id in one SI An area that initially only has BFR-ids in one SI
might end up with many SIs over a longer period of growth. Allocating SIs might end up with many SIs over a longer period of growth. Allocating SIs
to areas with initially sufficiently many spare bits for growths can help to areas that initially have sufficiently many spare bits for growth can help
to alleviate this issue. Or renumber BFERs after network expansion. In alleviate this issue. Alternatively, BFERs can be renumbered after network expan
this example one may consider to use 6 SIs and assign one to each area.</t> sion. In
this example, one may consider using six SIs and assigning one to each area.</t>
<t>This example shows that intelligent BFR-id allocation within at least <t>This example shows that intelligent BFR-id allocation within at l
sub-domain 0 can even be helpful or even necessary in BIER.</t> east
subdomain 0 can be helpful or even necessary in BIER.</t>
</section> </section>
<!-- with-bier -->
<section anchor="with-bier-te" title="With BIER-TE">
<t>In BIER-TE one needs to determine a subset of the physical topology <section anchor="with-bier-te" numbered="true" toc="default">
<name>With BIER-TE</name>
<t>In BIER-TE, one needs to determine a subset of the physical topol
ogy
and attached BFERs so that the "desired" representation of this topology and attached BFERs so that the "desired" representation of this topology
and the BFER fit into a single BitString. This process needs to be and the BFERs fit into a single BitString. This process needs to be
repeated until the whole topology is covered.</t> repeated until the whole topology is covered.</t>
<t>Once bits/SIs are assigned to the topology and BFERs, BFR-ids are
<t>Once bits/SIs are assigned to topology and BFERs, BFR-id is just a derived just a derived
set of identifiers from the operator/BIER-TE Controller as explained above.</t> set of identifiers from the operator / BIER-TE controller as explained above.</t
>
<t>Every time that different sub-topologies have overlap, bits need to <t>Whenever different subtopologies have overlap, bits need to
be repeated across the BitStrings, increasing the overall amount of bits be repeated across the BitStrings, increasing the overall amount of bits
required across all BitString/SIs. In the worst case, one assigns random subsets required across all BitStrings/SIs. In the worst case, one assigns random subset
of BFERs s of BFERs
to different SIs. This will result in an outcome much worse than in (non-TE) BIE to different SIs. This will result in an outcome much worse than in (non-TE) BIE
R: It R: it
maximizes the amount of unnecessary topology overlap across SI and therefore maximizes the amount of unnecessary topology overlap across SIs and therefore
reduces the number of BFER that can be reached across each individual SI. reduces the number of BFERs that can be reached across each individual SI.
Intelligent BFER to SI assignment and selecting specific "desired" subtopologies Intelligent BFER-to-SI assignment and selecting specific "desired" subtopologies
can can
minimize this problem.</t> minimize this problem.</t>
<t>To set up BIER-TE efficiently for the topology shown in <xref tar
<t>To set up BIER-TE efficiently for the topology of <xref target="scaling-pictu get="scaling-picture" format="default"/>, the following bit
re"/>, the following bit
allocation method can be used. This method can easily be expanded to allocation method can be used. This method can easily be expanded to
other, similarly structured larger topologies.</t> other, similarly structured larger topologies.</t>
<t>Each area is allocated one or more SIs, depending on the number o
<t>Each area is allocated one or more SIs depending on the number of future f future
expected BFERs and number of bits required for the topology in the area. expected BFERs and the number of bits required for the topology in the area.
In this example, 6 SIs, one per area.</t> In this example, six SIs are used, one per area.</t>
<t>In addition, we use four bits in each SI:</t>
<t>In addition, we use 4 bits in each SI: bia, bib, bea, beb: (b)it (i)ngress (a <dl spacing="normal">
), <dt>bia:</dt><dd>(b)it (i)ngress (a)</dd>
(b)it (i)ngress (b), (b)it (e)gress (a), (b)it (e)gress (b). These bits will be <dt>bib:</dt><dd>(b)it (i)ngress (b)</dd>
used to pass BIER <dt>bea:</dt><dd>(b)it (e)gress (a)</dd>
packets from any BFIR via any combination of ingress area a/b BFR and egress are <dt>beb:</dt><dd>(b)it (e)gress (b)</dd>
a </dl>
a/b BFR into a specific target area. These bits are then set up with the right <t>These bits will be used to pass BIER
forward_routed() adjacencies on the BFIR and area edge BFR:</t> packets from any BFIR via any combination of ingress area a/b BFRs and egress ar
ea
<t>On all BFIRs in an area j|j=1...6, bia in each BIFT:SI is populated with the a/b BFRs into a specific target area. These bits are then set up with the right
same forward_routed() adjacencies on the BFIRs and area edge BFRs as follows.</t>
forward_routed(BFRja), and bib with forward_routed(BFRjb). On all area <t>On all BFIRs in an area, j|j=1...6, bia in each BIFT:SI is popula
edge BFR, bea in BIFT:SI=k|k=1...6 is populated with forward_routed(BFRka) and ted with the same
forward_routed(BFRja) and bib with forward_routed(BFRjb). On all area
edge BFRs, bea in BIFT:SI=k|k=1...6 is populated with forward_routed(BFRka) and
beb in BIFT:SI=k with forward_routed(BFRkb).</t> beb in BIFT:SI=k with forward_routed(BFRkb).</t>
<t>For BIER-TE forwarding of a packet to a subset of BFERs across al
<t>For BIER-TE forwarding of a packet to a subset of BFERs across all areas, l areas,
a BFIR would create at most 6 copies, with SI=1...SI=6, In each packet, a BFIR would create at most six copies, with SI=1...SI=6. In each packet,
the bits indicate bits for topology and BFER in that topology plus the four bits the BitString includes bits for one area and the BFERs in that area, plus the fo
ur bits
to indicate whether to pass this packet via the ingress area a or b border BFR to indicate whether to pass this packet via the ingress area a or b border BFR
and the egress area a or b border BFR, therefore allowing path steering and the egress area a or b border BFR, therefore allowing path steering
for those two "unicast" legs: 1) BFIR to ingress area edge and 2) core to egress for those two "unicast" legs: 1) BFIR to ingress area edge and 2) core to egress
area edge. Replication only happens inside the egress areas. For BFER in the area edge. Replication only happens inside the egress areas. For BFERs that are
same area as in the BFIR, these four bits are not used.</t> in the
same area as the BFIR, these four bits are not used.</t>
</section> </section>
<!-- with-bier-te -->
</section> </section>
<!-- example -->
<section anchor="summary" title="Summary">
<t>BIER-TE can, like BIER, support multiple SIs within a sub-domain. This allows <section anchor="summary" numbered="true" toc="default">
to apply the mapping BFR-id = SI * BSL + BP. This allows to re-use <name>Summary</name>
the BIER architecture concept of BFR-id and therefore minimize BIER-TE specific <t>BIER-TE can, like BIER, support multiple SIs within a subdomain. Th
functions in possible is allows
application of the mapping BFR-id = SI * BSL + BP. This also permits the reuse o
f
the BIER architecture concept of BFR-ids and, therefore, minimization of BIER-TE
-specific functions in possible
BIER layer control plane mechanisms with BIER-TE, including flow overlay methods and BIER header fields.</t> BIER layer control plane mechanisms with BIER-TE, including flow overlay methods and BIER header fields.</t>
<t>The number of BFIRs/BFERs possible in a subdomain is smaller than i
<t>The number of BFIR/BFER possible in a sub-domain is smaller than in BIER n BIER
because BIER-TE uses additional bits for topology.</t> because BIER-TE uses additional bits for the topology.</t>
<t>Subdomains in BIER-TE can be used as they are in BIER to create mor
<t>Sub-domains (SDs) in BIER-TE can be used like in BIER to create more efficien e efficient
t
replication to known subsets of BFERs.</t> replication to known subsets of BFERs.</t>
<t>Assigning bits for BFERs intelligently into the right SI is more im
<t>Assigning bits for BFERs intelligently into the right SI is more important in portant in
BIER-TE than in BIER because of replication efficiency and overall amount of BIER-TE than in BIER because of replication efficiency and the overall amount of
bits required.</t> bits required.</t>
</section>
</section>
<!-- example -->
</section> </section>
<!-- mgmt-stuff -->
</section> </section>
<!-- controller-ops -->
<section anchor="security" title="Security Considerations">
<t>If <xref target="RFC8296"/> is used, BIER-TE shares its security consideratio
ns.</t>
<t>BIER-TE shares the security considerations of BIER, <xref target="RFC8279"/>, <section anchor="security" numbered="true" toc="default">
with <name>Security Considerations</name>
<t>If "<xref target="RFC8296" format="title"/>" <xref target="RFC8296" for
mat="default"/> is used, its security considerations also apply to BIER-TE.</t>
<t>The security considerations of "<xref target="RFC8279" format="title"/>
" <xref target="RFC8279" format="default"/> also apply to BIER-TE, with
the following overriding or additional considerations.</t> the following overriding or additional considerations.</t>
<t>BIER-TE forwarding explicitly supports unicast "tunneling" of BIER pack
<t>BIER-TE forwarding explicitly supports unicast "tunneling" of BIER packets vi ets via forward_routed()
a forward_routed()
adjacencies. The BIER domain security model is based on a subset of interfaces o n a BFR adjacencies. The BIER domain security model is based on a subset of interfaces o n a BFR
that connect to other BFRs of the same BIER domain. For BIER-TE, this security m odel equally applies that connect to other BFRs of the same BIER domain. For BIER-TE, this security m odel equally applies
to such unicast "tunneled" BIER packets. This does not only include the need to to such unicast "tunneled" BIER packets. This not only includes the need to filt
filter er
received unicast "tunneled" BIER packets to prohibit injection of such "tunneled received unicast "tunneled" BIER packets to prohibit the injection of such "tunn
" BIER eled" BIER
packets from outside the BIER domain, but also prohibiting forward_routed() adja packets from outside the BIER domain but also the need to prohibit forward_route
cencies d() adjacencies
to leak BIER packets from the BIER domain. It SHOULD be possible to configure from leaking BIER packets from the BIER domain. It <bcp14>SHOULD</bcp14> be poss
interfaces to be part of a BIER domain solely for sending and receiving of unica ible to configure
st interfaces to be part of a BIER domain solely for sending and receiving unicast
"tunneled" BIER packets even if the interface can not send/receive BIER encapsul "tunneled" BIER packets even if the interface cannot send/receive BIER encapsula
ated packets.</t> ted packets.</t>
<t>In BIER, the standardized methods for the routing underlays are IGPs
<t>In BIER, the standardized methods for the routing underlays are IGPs
with extensions to distribute BFR-ids and BFR-prefixes. with extensions to distribute BFR-ids and BFR-prefixes.
<xref target="RFC8401"/> specifies the extensions for IS-IS and <xref target="RF C8444"/> specifies the extensions for OSPF. <xref target="RFC8401" format="default"/> specifies the extensions for IS-IS, an d <xref target="RFC8444" format="default"/> specifies the extensions for OSPF.
Attacking the protocols for the BIER routing underlay or (non-TE) BIER layer con trol Attacking the protocols for the BIER routing underlay or (non-TE) BIER layer con trol
plane, or impairment of any BFR in a domain may lead to successful attacks plane, or the impairment of any BFRs in a domain, may lead to successful attacks
against the results of the routing protocol, enabling DoS attacks against against the information that BIER-TE learns from the routing protocol (routes, n
paths or the addressing (BFR-id, BFR-prefixes) used by BIER.</t> ext hops, BFR-ids, ...), enabling DoS attacks against
paths or the addressing (BFR-ids, BFR-prefixes) used by BIER.</t>
<t>The reference model for the BIER-TE layer control plane is a BIER-TE controll <t>The reference model for the BIER-TE layer control plane is a BIER-TE co
er. ntroller.
When such a controller is used, impairment of an individual BFR in a domain caus When such a controller is used, the impairment of an individual BFR in a domain
es causes
no impairment of the BIER-TE control plane on other BFRs. If a routing no impairment of the BIER-TE control plane on other BFRs. If a routing
protocol is used to support forward_routed() adjacencies, then this is still an protocol is used to support forward_routed() adjacencies, then this is still an
attack vector as in BIER, but only for BIER-TE forward_routed() adjacencies, and attack vector as in BIER, but only for BIER-TE forward_routed() adjacencies and
not other adjacencies.</t> not other adjacencies.</t>
<t>Whereas IGP routing protocols are most often not well secured through
<t>Whereas IGP routing protocols are most often not well secured through
cryptographic authentication and confidentiality, communications between control lers and routers such as those cryptographic authentication and confidentiality, communications between control lers and routers such as those
to be considered for the BIER-TE controller/control-plane can be and are much mo to be considered for the BIER-TE controller / control plane can be, and are, muc
re commonly h more commonly
secured with those security properties, for example by using Secure SHell (SSH), secured with those security properties -- for example, by using "Secure Shell" (
<xref target="RFC4253"/> for NETCONF (<xref target="RFC6242"/>), or via Transpo SSH) <xref target="RFC4253" format="default"/> for NETCONF <xref target="RFC6242
rt Layer Security (TLS), such as <xref target="RFC8253"/> for PCEP, <xref target " format="default"/>; or via "Transport Layer Security" (TLS), such as <xref tar
="RFC5440"/>, or <xref target="RFC7589"/> for NETCONF. BIER-TE controllers SHOUL get="RFC8253" format="default"/> for PCEP <xref target="RFC5440" format="default
D use security equal to or better than these mechanisms.</t> "/> or <xref target="RFC7589" format="default"/> for NETCONF. BIER-TE controller
s <bcp14>SHOULD</bcp14> use security equal to or better than these mechanisms.</
<t>When any of these security mechanisms/protocols are used for communications t>
<t>When any of these security mechanisms/protocols are used for communicat
ions
between a BIER-TE controller and BFRs, their security considerations apply to BI ER-TE. between a BIER-TE controller and BFRs, their security considerations apply to BI ER-TE.
In addition, the security considerations of PCE, <xref target="RFC4655"/> apply. In addition, the security considerations of "<xref target="RFC4655" format="titl
</t> e"/>" <xref target="RFC4655" format="default"/> apply.</t>
<t>The most important attack vector in BIER-TE is misconfiguration,
<t>The most important attack vector in BIER-TE is misconfiguration, either on the BFRs themselves or via the BIER-TE controller.
either on the BFR themselves or via the BIER-TE controller.
Forwarding entries with DNC could be set up to create persistent loops, in which Forwarding entries with DNC could be set up to create persistent loops, in which
packets only expire because of TTL. To minimize the impact of such attacks packets only expire because of TTL. To minimize the impact of such attacks
(or more likely unintentional misconfiguration by operators and/or bad BIER-TE c ontroller software), (or, more likely, unintentional misconfiguration by operators and/or bad BIER-TE controller software),
the BIER-TE forwarding rules are defined to be as strict in clearing the BIER-TE forwarding rules are defined to be as strict in clearing
bits as possible. The clearing of all bits with an adjacency on bits as possible. The clearing of all bits with an adjacency on
a BFR prohibits that a looping packet creates additional packet amplification a BFR prohibits a looping packet from creating additional packet amplification
through the misconfigured loop on the packet's second or further times around th through the misconfigured loop on the packet's second time or subsequent times a
e round the
loop, because all relevant adjacency bits would have been cleared on the first r ound loop, because all relevant adjacency bits would have been cleared on the first r ound
through the loop. In result, BIER-TE has the same degree of looping packets through the loop. As a result, looping packets can occur in BIER-TE to the same
as possible with unintentional or malicious loops in the routing underlay degree
with BIER or even with unicast traffic.</t> as is possible with unintentional or malicious loops in the routing underlay wit
h BIER, or even with unicast traffic.</t>
<t>Deployments where BIER-TE would likely be beneficial <t>Deployments where BIER-TE would likely be beneficial
may include operational models where actual configuration changes may include operational models where actual configuration changes
from the controller are only required during non-production phases of from the controller are only required during non-production phases of
the network's life-cycle, such as in embedded networks or in manufacturing the network's life cycle, e.g., in embedded networks or in manufacturing
networks during e.g. plant reworking/repairs. In these networks during such activities as plant reworking or repairs. In these
type of deployments, configuration changes could be locked out when the types of deployments, configuration changes could be locked out when the
network is in production state and could only be (re-)enabled through network is in production state and could only be (re-)enabled through
reverting the network/installation into non-production state. Such reverting the network/installation to non-production state. Such
security designs would not only allow to provide additional layers security designs would not only allow a deployment to provide additional layers
of protection against configuration attacks, but would foremost of protection against configuration attacks but would, first and foremost,
protect the active production process from such configuration attacks.</t> protect the active production process from such configuration attacks.</t>
</section>
</section> <section anchor="iana" numbered="true" toc="default">
<!-- security --> <name>IANA Considerations</name>
<t>This document has no IANA actions.</t>
<section anchor="iana" title="IANA Considerations"> </section>
</middle>
<t>This document requests no action by IANA. </t> <back>
</section>
<!-- iana -->
<section anchor="ack" title="Acknowledgements">
<t>The authors would like to thank Greg Shepherd, Ijsbrand Wijnands, Neale Ran
ns, Dirk Trossen, Sandy Zheng, Lou Berger, Jeffrey Zhang, Carsten Borman and Wol
fgang Braun for their reviews and suggestions.</t>
<t> Special thanks to Xuesong Geng for shepherding the document and for IESG r
eview/suggestions by Alvaro Retana (responsible AD/RTG), Benjamin Kaduk (SEC), T
ommy Pauly (TSV), Zaheduzzaman Sarker (TSV), Eric Vyncke (INT), Martin Vigoureux
(RTG), Robert Wilton (OPS), Eric Kline (INT), Lars Eggert (GEN), Roman Danyliv
(SEC), Ines Robles (RTGDIR), Robert Sparks (Gen-ART), Yingzhen Qu (RTGdir), Mart
in Duke (TSV).</t>
</section>
<!-- ack -->
<section anchor="changes" title="Change log [RFC Editor: Please remove]">
<t>draft-ietf-bier-te-arch:
<list>
<t>13:</t>
<t>Changed Gregs author association/email.</t>
<t>Fixed Nits in -12 from Ben Kaduk.</t>
<t>Fixed Alvaro's concerns: (1) Removed references to SR in Abstract/Overv
iew (2) removed section 4.5.</t>
<t>12:</t>
<t>AD review Alvaro Retana.</t>
<t>Various textual/editorial nits including adding () to all instances of
forwarding adjacency name instances.</t>
<t>3.1 Added new paragraph outlining possible use of BGP as RR in BIER-TE
controller
as core of multicast flow overlay component of BIER-TE.</t>
<t>3.2 added xref's to relevant sections to the listed control plane point
s.</t>
<t>4.1 rewrote paragraphs of 4.1 leading up to Figure 4. to eliminate any
confusion in
how the BIFT work and how it compares to the notions in rfc8279, as wel
l as better
linking it to the Pseudocode.</t>
<t>Moved SR section into appendix.</t>
<t>TSV review Martin Duke.</t>
<t>Text/editorial nits.</t>
<t>4.4 improved text describing handling of F-BM.</t>
<t>RTGdir review Yingzhen Qu.</t>
<t>Various text/editorial nits.</t>
<t>Added notion that BitStrings represent loop free tree for packet to abs
tract and intro.</t>
<t>Various text nit and editorial improvements.</t>
<t>Fixed some BFR-id field -> BFIR-id field mistakes.</t>
<t>Capitalized NETCONF/RESTCONF/YANG, added RFC references.</t>
<t>Improved Figure 16 with explicitly two links into BFR3 and explanatory
text.</t>
<t>Gen-ART review Robert Sparks.</t>
<t>Various textual nits, editorial improvements.</t>
<t>3.2 Introduced terms "BIER-TE topology control" and "BIER-TE tree contr
ol" for the two functional components of the control plane. </t>
<t>3.2.1 - 3.2 change introduces the open RFC-editor issue of appropriate
xrfs (to be resolved by RFC-editor).</t>
<t>3.3 Rewrote last paragraph to better describe loop prevention through c
learing of bits in BitString.</t>
<t>4.1 Fixed up text/formula describing mapping between bfr-id, SI:BP and
SI,BSL and BP. Fix offset bug.</t>
<t>5.3.6.2 Improved description paragraph explaining overlap of topology f
or different SI.</t>
<t>5.3.7 Improved first summary paragraph.</t>
<t>7. Rephrased applicability statement of control plane protocol security
considerations to BIER-TE security.</t>
<t>RTGDIR review Ines Robles.</t>
<t>Fixed up adjacencies in Example 2 and explanation text to be explicit a
bout which BFR not
only passes, but also receives the packet.</t>
<t>7. (security considerations). Added paragraph about forward_routed() an
d prohibiting BIER packet leaking in/out of domain.</t>
<t>IESG review Roman Danyliv (SEC).</t>
<t>Several textual/sentence nits/editorials.</t>
<t>IESG review Lars Eggert (GEN).</t>
<t>Various good editorial word fixed.</t>
<t>Pointer to non-false-positive bloom filter work that looks like it happ
ened after our IETF discussions documented in this doc, so will not add it to do
c, but here is URL for folks interested: https://ieeexplore.ieee.org/document/84
86415.</t>
<t>Did not change "native" to a different word for inclusivity because of
my worry there is no estavblished single replacement word, making reading/search
ing/understanding more difficult.</t>
<t>IESG review Martin Vigeureux (RTG).</t>
<t>Added back reference to RFC8402. Textual fixes.</t>
<t>IESG review Eric Kline (INT).</t>
<t>2.1 Fixed typo in BFR* explanations.</t>
<t>4.3 Added explanatio about MTU handling.</t>
<t>IESG review Eric Vyncke (INT).</t>
<t>Fixed up initial text to introduce various abbreviations.</t>
<t>2.4 refined wording to "with the _intent_ to easily build common forwar
ding planes...".</t>
<t>4.2.3 refined text about entropy in ECMP - now taken text from rfc8279.
</t>
<t>IESG review Zaheduzzaman Sarker (TSV).</t>
<t>5.1.7 Refined text explaining documentation of ECMP algorithm.</t>
<t>5.3.6.2. fixed range of areas/SI over which to build the example large
network BPs - removed explanation of the large network shown to be only used for
sources in area 1 (IPTV), because it was a stale explanation.</t>
<t>IESG review Ben Kaduk (round 2):</t>
<t>4.4 Advanced pseudocode still had one wrong "~". Root cause seems to ha
ve been day 0 problem in pseudocode written for -01, "~" was inserted in the wro
ng one of two code lines. Also enhanced textual description and comments in pseu
docode, changed variable name AdjacentBits to PktAdjacentBits to avoid confusion
with AdjacentBits[SI].</t>
<t>5.1.3 Rewrote last two paragraphs explaining the sharing of bit positio
ns for lead-BFER hopefully better. Also detailled how it interacts with other op
timizations and the type of payload BIER-TE packets may carry.</t>
<t>4.4 (from Carsten Borman) changed spacing in pseudocode to be consisten
t. Fixed {VRF}, clarified pseudocode object syntax, typos.</t>
<t>11: IESG review Ben Kaduk, summary:</t>
<t>One discuss for bug in pseudocode. turned out to be one cahrcter typo.<
/t>
<t>Added (non-TE) prefix in places where BIER by itsels had to be better d
isambiguated.</t>
<t>enhanced text for hub-and-spoke to indicate we're only talking about hu
b to spoke traffic.</t>
<t> long list ot language fixes/improvement (nits). Thanks a lot!.</t>
<t>add suggestion to SHOULD use known confidentiality protocols between co
ntroller and BFR.</t>
<t>10: AD review Alvaro Retana, summary:</t>
<t>Note: rfcdiff shows more changes than actually exist because text moved aroun
d.</t>
<t>Summary:<list style="numbers">
<t>restructuring: merged all controller sections under common controller ops ma
in section, moved unfitting stuff out to other parts of doc. Split Intro section
into Overview and Intro. Shortened Abstract, moved text into Overview,
added sections overview.</t>
<t>enhanced/rewrote: 2.3 Comparison with -> Relationship to BIER-TE</t>
<t>enhanced/rewrote: 3.2 BIER-TE controller -> BIER-TE control plane, 3.2.1 BIE
R-TE controller, for consistency with rfc8279</t>
<t>additional subsections for Alvaros asks</t>
<t>added to: 3.3 BIER-TE forwarding plane (consistency with rfc8279)</t>
<t>Enhanced description of 4.3/encap considerations to better explain how BIER/
BIER-TE can run together.</t>
</list></t>
<t>Notation: Markers (a),(b),... at end of points are references from the review discussion with Alvaro to the changes made.</t> <displayreference target="I-D.ietf-roll-ccast" to="CONSTRAINED-CAST"/>
<t>Details:.</t> <references>
<t>Throughout text: changed term spelling to rfc8279 - bit positions, sub-domai <name>References</name>
n, ... (i).</t> <references>
<t>Reset changed to clear, also DNR changed to DNC (Do Not Clear) (q).</t> <name>Normative References</name>
<t>Abstract: Shortened. Removed name explanation note (Tree Engineering), (a).< <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
/t> FC.2119.xml"/>
<t>1. Introduction -> Overview: Moved important explanation paragraph from abst <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
ract to Introduction. Fixed text, (a).</t> FC.8279.xml"/>
<t> Added bullet point list explanation of structure of document (e).</t> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<t> Renamed to Overview because that is now more factually correct.</t> FC.8174.xml"/>
<t>1.1. Fixed bug in example adding bit p15.(l).</t> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<t>2. (New - Introduction): Moved section 1.1 - 1.3 (examples, comparison with FC.8296.xml"/>
BIER-TE) from Introduction into new "Overview" section. Primarily so that "requi </references>
rements language" section (at end of Introduction) is not in middle of document <references>
after all the Introduction.</t> <name>Informative References</name>
<t>2.1 Removed discussion of encap, moved to 4.2.2 (m).</t> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<t>2.2 enhanced paragraph suggesting native/overlay topology types, also sugest FC.4253.xml"/>
type hybrid (n).</t> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<t>2.3 Overhauled comparison text BIER/BIER-TE, structured into common, differe FC.4456.xml"/>
nt, not-required-by-te, integration-bier-bier-te. Changed title to "Relationship <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
" to allow including last point. (f).</t> FC.4655.xml"/>
<t>2.4 moved Hardware forwarding comparison section into section 2 to allow coa <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
lescing of sections into section 5 about the controller operations (hardware for FC.5440.xml"/>
warding was in the middle of it, wrong place). Shortened/improved third paragrap <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
h by pointing to BIFT as deciding element for selection between BIER/BIER-TE. Re FC.6241.xml"/>
moved notion of experimentation (this now targets standard) (g).</t> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<t>3. (Components): Aligned component name and descriptions better with RFC8279 FC.6242.xml"/>
. Now describe exactly same three layers. BIER layer constituted from BIER-TE c <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
ontrol plane and BIER-TE forwarding plane. BIER-TE controller is now simply comp FC.7589.xml"/>
onent of BIER-TE control plane. (b).</t> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<t>3.1. shortened/improved paragraph explaining use of SI:BP instead of also bf FC.7752.xml"/>
r-id as index into BIFT, rewrote paragraph talking about reuse of BPs(o).</t> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<t>3.2. rewrote explanation of BIER-TE control plane in the style of RFC8729 Se FC.7950.xml"/>
ction 4.2 (BIER layer) with numbered points. Note that RFC8729 mixes control and <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
forwarding plane bullet points (this doc does not). Merged text from old sectio FC.7988.xml"/>
ns 2.2.1 and 2.2.3 into list. (b).</t> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<t>3.2.1. Expanded/improved explanation of BIER-TE Controller (b).</t> FC.8040.xml"/>
<t>3.2.1.1. Added subsection for topology discovery and creation (d).</t> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<t>3.2.1.2. Added subsection for engineered BitStrings as key novel aspect not FC.8253.xml"/>
found in BIER. (X).</t> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<t>3.3. Added numbered list for components of BIER-TE forwarding plane (complet FC.8345.xml"/>
ing the comparable text from RFC8729 Section 4.2).</t> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<t>3.4 Alvaro does not mind additional example, fixed bugs.</t> FC.8401.xml"/>
<t>3.5 Removed notion about using IGP BIER extensions for BIER-TE, such as BIFT <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
address ranges. After -10 making use of BIFT clearer, it now looks to authors a FC.8402.xml"/>
s if use of IGP extensions would not be beneficial, as long as we do need to use <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
the BIER-TE controller, e.g. unlike in BIER, a BFR could not learn from the IGP FC.8444.xml"/>
information what traffic to send towards a particular BIFT-ID, but instead that <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
is the core of what the controller needs to provide.</t> FC.8556.xml"/>
<t>4.2.2 Improved text to explain requirement to identify BIER-TE in the tunnel
encap and compress description of use-cases (m).</t>
<t>4.2.3 enhanced ECMP text (p).</t>
<t>4.3. rewrote most of Encapsulation Considerations to better explain to Alvar
os question re sharing or not sharing SD via BIER/BIER-TE. Added reference to I-
D.ietf-bier-non-mpls-bift-encoding as a very helpful example. (f).</t>
<t>4.3 Renamed title to "...Co-Existence with BIER" as this is what it is about
and to help finding it from abstract/intro ("co-exist") (j).</t>
<t>4.4. Moved BIER-TE Forwarding Pseudocode here to coalesce text logically. Ch
anged text to better compare with BIER pseudo forwarding code. Numerical list of
how F-BM works for BIER-TE. Removed efficiency comparison with BIER (too diffic
ult to provide sufficient justification, derails from focus of section) (j).</t>
<t>4.6. (Requirements) Restructured: Removed notion of "basic" BIER-TE forwardi
ng, simply referring to it now as "mandatory" BIER-TE forwarding. Cleaned up tex
t to have requirements for different adjacencies in different paragraphs. (c).</
t>
<t>5. Created new main section "BIER-TE Controller operational considerations",
coalesced old sections 4., 5., 7. into this new main section. No text changes.
(k).</t>
<t>5.1.9 Added new separate picture instead of referring to a picture later in
text, adjusted text (r).</t>
<t>5.3.2 Changed title to not include word "comparison" to avoid this being acc
ounted against Alvaros concern about scattering comparison (IMHO text already ha
s little comparison, so title was misleading) (h).</t>
<t>co-authors internal review:</t> <!-- draft-ietf-teas-rfc3272bis (I-D Exists)
<t>4.4 Added xref to Figure 5.</t> (have to do "long way" because Adrian Farrel is editor) -->
<t>5.2.1 Duplicated ring picture, added visuals for described miswiring (s).</t <reference anchor="TE-OVERVIEW">
> <front>
<t>5.2.2 replace "topology" with graph (wrong word).</t> <title>Overview and Principles of Internet Traffic Engineering</title>
<t>5.3.3 rewrote explanation of how to map BFR-id to SI:BP and assign them, cla <author fullname="Adrian Farrel" surname="Farrel" initials="A" role="edito
rified BFR-id is option. Retitled to better explain scope of section.</t> r">
<t>5.3.4 Removed considerations in 5.3.4 for sharing BFR-id across BIER/BIER-TE </author>
(t), changed title to explain how BFIR/BIER-TE controller interactions need som <date month="September" day="11" year="2022" />
e form of identifying BFR but this does not have to be BFR-id.</t> </front>
<t>7. Added new security considerations (u).</t> <seriesInfo name="Internet-Draft" value="draft-ietf-teas-rfc3272bis-21" />
<t></t> </reference>
<t>09: Incorporated fixes for feedback from Shepherd (Xuesong Geng).</t> <!-- draft-ietf-bier-multicast-http-response (Expired)
<t> Added references for Bloom Filters and Rate Controlled Service Disc (have to do "long way" to fix Toerless Eckert's initial) -->
iplines.</t> <reference anchor="BIER-MCAST-OVERLAY">
<t> 1.1 Fixed numbering of example 1 topology explanation. Improved lan <front>
guage on second example (less abbreviating to avoid confusion about meaning).</t <title>Applicability of BIER Multicast Overlay for Adaptive Streaming Serv
> ices</title>
<t> 1.2 Improved explanation of BIER-TE topology, fixed terminology of <author initials="D." surname="Trossen" fullname="Dirk Trossen">
graphs (BIER-TE topology is a directed graph where the edges are the adjacencies <organization>Huawei Technologies Duesseldorf GmbH</organization>
).</t> </author>
<t> 2.4 Fixed and amended routing underlay explanations: detailed why n <author initials="A." surname="Rahman" fullname="Akbar Rahman">
o need for BFER routing underlay routing protocol extensions, but potential to r <organization>InterDigital Communications, LLC</organization>
e-use BIER routing underlay routing protocol extensions for non-BFER related ext </author>
ensions.</t> <author initials="C." surname="Wang" fullname="Chonggang Wang">
<t> 3.1 Added explanation for VRF and its use in adjacencies.</t> <organization>InterDigital Communications, LLC</organization>
<t>08: Incorporated (with hopefully acceptable fixes) for Lou suggested se </author>
ction 2.5, TE considerations.</t> <author initials="T." surname="Eckert" fullname="Toerless Eckert">
<t> Fixes are primarily to the point to a) emphasize that BIER-TE does <organization>Futurewei Technologies Inc.</organization>
not depend on the routing underlay unless forward_routed() adjacencies are used, </author>
and b) that the allocation and tracking of resources does not explicitly have t <date month="July" day="10" year="2021" />
o be tied to BPs, because they are just steering labels. Instead, it would ideal </front>
ly come from per-hop resource management that can be maintained only via local a <seriesInfo name="Internet-Draft" value="draft-ietf-bier-multicast-http-respo
ccounting in the controller.</t> nse-06" />
<t>07: Further reworking text for Lou.</t> </reference>
<t> Renamed BIER-PE to BIER-TE standing for "Tree Engineering" after vo
tes from BIER WG.</t>
<t> Removed section 1.1 (introduced by version 06) because not consider
ed necessary in this doc by Lou (for framework doc).</t>
<t> Added [RFC editor pls. remove] Section to explain name change to fu
ture reviewers.</t>
<t>06: Concern by Lou Berger re. BIER-TE as full traffic engineering solut
ion.</t>
<t> Changed title "Traffic Engineering" to "Path Engineering"</t>
<t> Added intro section of relationship BIER-PE to traffic engineering.
</t>
<t> Changed "traffic engineering" term in text" to "path engineering",
where appropriate</t>
<t> Other:</t>
<t> Shortened "BIER-TE Controller Host" to "BIER-TE Controller". Fixed
up all instances of controller to do this.</t>
<t>05: Review Jeffrey Zhang.</t>
<t> Part 2:</t>
<t> 4.3 added note about leaf-BFER being also a propery of routing setu
p.</t>
<t> 4.7 Added missing details from example to avoid confusion with rout
ed adjacencies, also compressed explanatory text and better justification why se
ed is explicitly configured by controller.</t>
<t> 4.9 added section discussing generic reuse of BP methods.</t>
<t> 4.10 added section summarizing BP optimizations of section 4.</t>
<t> 6. Rewrote/compressed explanation of comparison BIER/BIER-TE forwar
ding difference. Explained benefit of BIER-TE per-BP forwarding being independen
t of forwarding for other BPs.</t>
<t> Part 1:</t>
<t> Explicitly ue forwarded_connected adjcency in ECMP adjcency example
s to avoid confusion.</t>
<t> 4.3 Add picture as example for leav vs. non-leaf BFR in topology. I
mproved description.</t>
<t> 4.5 Exampe for traffic that can be broadcast -> for single BP in hu
b&amp;spoke.</t>
<t> 4.8.1 Simplified example picture for routed adjacency, explanatory
text.</t>
<t> Review from Dirk Trossen:</t>
<t> Fixed up explanation of ICC paper vs. bloom filter.</t>
<t>04: spell check run.</t>
<t> Addded remaining fixes for Sandys (Zhang Zheng) review:</t>
<t> 4.7 Enhance ECMP explanations:</t>
<t> example ECMP algorithm, highlight that doc does not standardize ECM
P algorithm.</t>
<t> Review from Dirk Trossen:</t>
<t> 1. Added mentioning of prior work for traffic engineered paths with
bloom filters.</t>
<t> 2. Changed title from layers to components and added "BIER-TE contr
ol plane" to "BIER-TE Controller" to make it clearer, what it does.</t>
<t> 2.2.3. Added reference to I-D.ietf-bier-multicast-http-response as
an example solution.</t>
<t> 2.3. clarified sentence about resetting BPs before sending copies (
also forgot to mention DNR here).</t>
<t> 3.4. Added text saying this section will be removed unless IESG rev
iew finds enough redeeming value in this example given how -03 introduced sectio
n 1.1 with basic examples.</t>
<t> 7.2. Removed explicit numbers 20%/80% for number of topology bits i
n BIER-TE, replaced with more vague (high/low) description, because we do not ha
ve good reference material Added text saying this section will be removed unless
IESG review finds enough redeeming value in this example given how -03 introduc
ed section 1.1 with basic examples.</t>
<t> many typos fixed. Thanks a lot.</t>
<t>03: Last call textual changes by authors to improve readability:</t>
<t> removed Wolfgang Braun as co-authors (as requested).</t>
<t> Improved abstract to be more explanatory. Removed mentioning of FRR
(not concluded on so far).</t>
<t> Added new text into Introduction section because the text was too d
ifficult to jump into
(too many forward pointers). This primarily consists of examples an
d the early introduction
of the BIER-TE Topology concept enabled by these examples.</t>
<t> Amended comparison to SR.</t>
<t> Changed syntax from [VRF] to {VRF} to indicate its optional and to
make idnits happy.</t>
<t> Split references into normative / informative, added references.</t
>
<t>02: Refresh after IETF104 discussion: changed intended status back to s
tandard. Reasoning:</t>
<t> Tighter review of standards document == ensures arch will be better
prepared for possible adoption by other WGs (e.g. DetNet) or std. bodies.</t>
<t> Requirement against the degree of existing implementations is self
defined by the WG. BIER WG seems to think it is not necessary to apply multiple
interoperating implementations against an architecture level document at this ti
me to make it qualify to go to standards track. Also, the levels of support intr
oduced in -01 rev. should allow all BIER forwarding engines to also be able to s
upport the base level BIER-TE forwarding.</t>
<t>01: Added note comparing BIER and SR to also hopefully clarify BIER-TE
vs. BIER comparison re. SR.</t>
<t> - added requirements section mandating only most basic BIER-TE forward
ing features as MUST.</t>
<t> - reworked comparison with BIER forwarding section to only summarize a
nd point to pseudocode section.</t>
<t> - reworked pseudocode section to have one pseudocode that mirrors the
BIER forwarding pseudocode to make comparison easier and a second pseudocode tha
t shows the complete set of BIER-TE forwarding options and simplification/optimi
zation possible vs. BIER forwarding. Removed MyBitsOfInterest (was pure optimiza
tion).</t>
<t> - Added captions to pictures.</t>
<t> - Part of review feedback from Sandy (Zhang Zheng) integrated.</t>
<t>00: Changed target state to experimental (WG conclusion), updated refer
ences, mod auth association.</t>
<t> - Source now on https://www.github.com/toerless/bier-te-arch</t>
<t> - Please open issues on the github for change/improvement requests to
the document - in addition to posting them on the list (bier@ietf.). Thanks!.</t
>
</list>
</t>
<t>draft-eckert-bier-te-arch:
<list>
<t>06: Added overview of forwarding differences between BIER, BIER-TE.</t>
<t>05: Author affiliation change only.</t>
<t>04: Added comparison to Live-Live and BFIR to FRR section (Eckert).</t>
<t>04: Removed FRR content into the new FRR draft [I-D.eckert-bier-te-frr]
(Braun).</t>
<t> - Linked FRR information to new draft in Overview/Introduction</t>
<t> - Removed BTAFT/FRR from "Changes in the network topology"</t>
<t> - Linked new draft in "Link/Node Failures and Recovery"</t>
<t> - Removed FRR from "The BIER-TE Forwarding Layer"</t>
<t> - Moved FRR section to new draft</t>
<t> - Moved FRR parts of Pseudocode into new draft</t>
<t> - Left only non FRR parts</t>
<t> - removed FrrUpDown(..) and //FRR operations in ForwardBierTePacket(..
)</t>
<t> - New draft contains FrrUpDown(..) and ForwardBierTePacket(Packet) fro
m bier-arch-03</t>
<t> - Moved "BIER-TE and existing FRR to new draft</t>
<t> - Moved "BIER-TE and Segment Routing" section one level up</t>
<t> - Thus, removed "Further considerations" that only contained this sect
ion</t>
<t> - Added Changes for version 04</t>
<t></t>
<t>03: Updated the FRR section. Added examples for FRR key concepts. Add
ed BIER-in-BIER tunneling as option for tunnels in backup paths. BIFT structure
is expanded and contains an additional match field to support full node protect
ion with BIER-TE FRR.</t>
<t>03: Updated FRR section. Explanation how BIER-in-BIER encapsulation pr
ovides P2MP protection for node failures even though the routing underlay does n
ot provide P2MP.</t>
<t>02: Changed the definition of BIFT to be more inline with BIER. In revs
. up to -01, the idea was that a BIFT has only entries for a single BitString, a
nd every SI and sub-domain would be a separate BIFT. In BIER, each BIFT covers a
ll SI. This is now also how we define it in BIER-TE.</t>
<t>02: Added <xref target="mgmt-stuff"/> to explain the use of SI, sub-dom
ains and BFR-id in BIER-TE and to give an example how to efficiently assign bits
for a large topology requiring multiple SI.</t>
<t>02: Added further detailed for rings - how to support input from all ri
ng nodes.</t>
<t>01: Fixed BFIR -> BFER for section 4.3.</t>
<t>01: Added explanation of SI, difference to BIER ECMP, consideration for
Segment Routing, unicast FRR, considerations for encapsulation, explanations of
BIER-TE Controller and CLI.</t>
<t>00: Initial version.</t>
</list>
</t>
</section>
<!-- changes -->
</middle> <!-- draft-eckert-bier-te-frr (Expired)
(have to do "long way" to fix Toerless Eckert's initial) -->
<reference anchor="BIER-TE-PROTECTION">
<front>
<title>Protection Methods for BIER-TE</title>
<author initials="T." surname="Eckert" fullname="Toerless Eckert">
<organization>Huawei USA - Futurewei Technologies Inc.</organization>
</author>
<author initials="G." surname="Cauchie" fullname="Gregory Cauchie">
<organization>Bouygues Telecom</organization>
</author>
<author initials="W." surname="Braun" fullname="Wolfgang Braun">
<organization>University of Tuebingen</organization>
</author>
<author initials="M." surname="Menth" fullname="Michael Menth">
<organization>University of Tuebingen</organization>
</author>
<date month="March" day="5" year="2018" />
</front>
<seriesInfo name="Internet-Draft" value="draft-eckert-bier-te-frr-03" />
</reference>
<back> <!-- draft-ietf-roll-ccast (Expired) -->
<xi:include href="https://datatracker.ietf.org/doc/bibxml3/reference.I-D.ietf-ro
ll-ccast.xml"/>
<references title="Normative References"> <!-- draft-ietf-bier-te-yang (I-D Exists)
&RFC2119; (have to do "long way" to get correct capping of "Hu" and fix
&RFC8279; erroneous "chenhuanan" for H. Chen -->
&RFC8174; <reference anchor="BIER-TE-YANG">
&RFC8296; <front>
</references> <title>A YANG data model for Tree Engineering for Bit Index Explicit Repli
cation (BIER-TE)</title>
<author initials="Z." surname="Zhang" fullname="Zheng Zhang">
<organization>ZTE Corporation</organization>
</author>
<author initials="C." surname="Wang" fullname="Cui(Linda) Wang">
<organization>Individual</organization>
</author>
<author initials="R." surname="Chen" fullname="Ran Chen">
<organization>ZTE Corporation</organization>
</author>
<author initials="F." surname="Hu" fullname="fangwei hu">
<organization>Individual</organization>
</author>
<author initials="M." surname="Sivakumar" fullname="Mahesh Sivakumar">
<organization>Juniper networks</organization>
</author>
<author initials="H." surname="Chen" fullname="Huanan Chen">
<organization>China Telecom</organization>
</author>
<date month="May" day="1" year="2022" />
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-bier-te-yang-05" />
</reference>
<references title="Informative References"> <!-- draft-ietf-bier-non-mpls-bift-encoding (Expired)
&RFC4253; (have to do "long way" to get "IJ. Wijnands" and "M. Mishra") -->
&RFC4456; <reference anchor="NON-MPLS-BIER-ENCODING">
&RFC4655; <front>
&RFC5440; <title>An Optional Encoding of the BIFT-id Field in the non-MPLS BIER Enca
&RFC6241; psulation</title>
&RFC6242; <author fullname="IJsbrand Wijnands" surname="Wijnands" initials="IJ"></aut
&RFC7589; hor>
&RFC7752; <author fullname="Mankamana Mishra" surname="Mishra" initials="M"></author>
&RFC7950; <author fullname="Xiaohu Xu" surname="Xu" initials="X"></author>
&RFC7988; <author fullname="Hooman Bidgoli" surname="Bidgoli" initials="H"></author>
&RFC8040; <date month="May" day="30" year="2021" />
&RFC8253; </front>
&RFC8345; <seriesInfo name="Internet-Draft" value="draft-ietf-bier-non-mpls-bift-encoding
&RFC8401; -04" />
&RFC8402; </reference>
&RFC8444;
&RFC8556;
<!--
&RFC2205;
&RFC2212;
&RFC3209;
<?rfc include="reference.I-D.eckert-teas-bier-te-framework"?>
<?rfc include="reference.I-D.qiang-detnet-large-scale-detnet"?>
<?rfc include="reference.I-D.ietf-teas-rfc3272bis"?> <reference anchor="ICC" target="https://ieeexplore.ieee.org/document/751
<?rfc include="reference.I-D.ietf-bier-multicast-http-response"?> 1036">
<?rfc include="reference.I-D.eckert-bier-te-frr"?> <front>
<?rfc include="reference.I-D.ietf-roll-ccast"?> <title>
<?rfc include="reference.I-D.ietf-bier-te-yang"?>
<?rfc include="reference.I-D.ietf-bier-non-mpls-bift-encoding"?>
<reference anchor="ICC" target="https://ieeexplore.ieee.org/document/75110
36">
<front>
<title>
Stateless multicast switching in software defined networks Stateless multicast switching in software defined networks
</title> </title>
<author initials="M. J." surname="Reed"/> <author initials="M. J." surname="Reed"/>
<author initials="M." surname="Al-Naday"/> <author initials="M." surname="Al-Naday"/>
<author initials="N." surname="Thomos"/> <author initials="N." surname="Thomos"/>
<author initials="D." surname="Trossen"/> <author initials="D." surname="Trossen"/>
<author initials="G." surname="Petropoulos"/> <author initials="G." surname="Petropoulos"/>
<author initials="S." surname="Spirou"/> <author initials="S." surname="Spirou"/>
<date month="May" year="2016"/> <date month="May" year="2016"/>
</front> </front>
<seriesInfo name="" value="IEEE International Conference on Communicatio <refcontent>IEEE International Conference on Communications (ICC), Kua
ns (ICC), Kuala Lumpur, Malaysia, 2016"/> la Lumpur, Malaysia</refcontent>
</reference> <seriesInfo name="DOI" value="10.1109/ICC.2016.7511036"/>
</reference>
<reference anchor="RCSD94" target="https://dl.acm.org/doi/10.5555/2692227. <reference anchor="RCSD94" target="https://content.iospress.com/articles
2692232"> /journal-of-high-speed-networks/jhs3-4-05">
<front> <front>
<title> <title>
Rate-Controlled Service Disciplines Rate-Controlled Service Disciplines
</title> </title>
<author initials="H." surname="Zhang"/> <author initials="H." surname="Zhang"/>
<author initials="D." surname="Domenico"/> <author initials="D." surname="Ferrari"/>
<date month="May" year="1994"/> <date month="October" year="1994"/>
</front> </front>
<seriesInfo name="" value="Journal of High-Speed Networks, 1994"/> <refcontent>Journal of High Speed Networks, Volume 3, Issue 4, pp. 389
</reference> -412</refcontent>
<seriesInfo name="DOI" value="10.3233/JHS-1994-3405"/>
<reference anchor="Bloom70"> </reference>
<front>
<title>Space/time trade-offs in hash coding with allowable errors</tit
le>
<author initials="B. H." surname="Bloom" fullname="Burton H. Bloom">
<organization/>
</author>
<date month="July" year="1970"/>
</front>
<seriesInfo name="Comm. ACM " value="13(7):422-6"/>
<format type="PDF" target="https://dl.acm.org/doi/10.1145/362686.362692"
/>
</reference>
<!-- TODO change reference below as soon as its available from tool chain-
->
<!-- <?rfc include="reference.I-D.eckert-bier-te-frr"?> -->
<!----> <reference anchor="Bloom70" target="https://dl.acm.org/doi/10.1145/36268
6.362692">
<front>
<title>Space/time trade-offs in hash coding with allowable errors</t
itle>
<author initials="B. H." surname="Bloom" fullname="Burton H. Bloom">
<organization/>
</author>
<date month="July" year="1970"/>
</front>
<refcontent>Comm. ACM 13(7):422-6</refcontent>
<seriesInfo name="DOI" value="10.1145/362686.362692"/>
</reference>
</references> </references>
</references>
<section anchor="SR" title="BIER-TE and Segment Routing (SR)"> <section anchor="SR" numbered="true" toc="default">
<name>BIER-TE and Segment Routing (SR)</name>
<t>SR (<xref target="RFC8402"/>) aims to enable lightweight path steering <t>SR <xref target="RFC8402" format="default"/> aims to enable lightweight
via loose source routing. Compared to its more heavy-weight predecessor RSVP-TE, path steering
SR does for example not require per-path signaling to each of these hops.</t> via loose source routing. For example, compared to its more heavyweight predeces
sor, RSVP-TE, SR does not require per-path signaling to each of these hops.</t>
<t>BIER-TE supports the same design philosophy for multicast. <t>BIER-TE supports the same design philosophy for multicast.
Like in SR, it relies on source-routing - Like SR, BIER-TE</t>
via the definition of a BitString. Like SR, it only requires to consider <ul spacing="normal">
the "hops" on which either replication has to happen, or across which the <li>relies on source routing (via a BitString), and</li>
traffic should be steered (even without replication). Any other hops can <li>only requires consideration of
the "hops" either (1) on which replication has to happen or (2) across which the
traffic should be steered (even without replication).</li>
</ul>
<t>Any other hops can
be skipped via the use of routed adjacencies.</t> be skipped via the use of routed adjacencies.</t>
<t>BIER-TE "bit positions" (BPs) can be understood as the BIER-TE equivale
<t>BIER-TE bit position (BP) can be understood as the BIER-TE equivalent of nt of
"forwarding segments" in SR, but they have a different scope than SR forwarding "forwarding segments" in SR, but they have a different scope than do forwarding
segments. Whereas forwarding segments in SR are global or local, BPs in BIER-TE segments in SR. Whereas forwarding segments in SR are global or local, BPs in BI
have a scope that is the group of BFR(s) that have adjacencies for this BP in ER-TE
their BIFT. This can be called "adjacency" scoped forwarding segments.</t> have a scope that is comprised of one or more BFRs that have adjacencies for the
BPs in
<t>Adjacency scope could be global, but then every BFR would need an adjacency their BIFTs. These segments can be called "adjacency-scoped" forwarding segments
for this BP, for example a forward_routed() adjacency with encapsulation to .</t>
the global SR SID of the destination. Such a BP would always result in ingress <t>Adjacency scope could be global, but then every BFR would need an adjac
replication though (as in <xref target="RFC7988"/>). The first BFR encountering ency
this BP would directly for a given BP -- for example, a forward_routed() adjacency with encapsulation t
replicate to it. Only by using non-global adjacency scope for BPs can o
traffic be steered and replicated on non-ingress BFR.</t> the global SR "Segment Identifier" (SID) of the destination. Such a BP would alw
ays result in ingress
<t>SR can naturally be combined with BIER-TE and help to optimize it. For exampl replication, though (as in <xref target="RFC7988" format="default"/>). The first
e, BFR encountering this BP would directly
replicate traffic on it. Only by using non-global adjacency scope for BPs can
traffic be steered and replicated on a non-BFIR.</t>
<t>SR can naturally be combined with BIER-TE and can help optimize it. For
example,
instead of defining bit positions for non-replicating hops, it is equally instead of defining bit positions for non-replicating hops, it is equally
possible to use segment routing encapsulations (e.g. SR-MPLS label stacks) possible to use SR encapsulations (e.g., SR-MPLS label stacks)
for the encapsulation of "forward_routed" adjacencies.</t> for the encapsulation of "forward_routed()" adjacencies.</t>
<t>Note that (non-TE) BIER itself can also be seen as being similar to SR.
<t>Note that (non-TE) BIER itself can also be seen to be similar to SR. BIER BPs BIER BPs act
act as global destination Node-SIDs, and the BIER BitString is simply a highly optim
as global destination Node-SIDs and the BIER BitString is simply a highly optimi ized
zed
mechanism to indicate multiple such SIDs and let the network take care of effect ively mechanism to indicate multiple such SIDs and let the network take care of effect ively
replicating the packet hop-by-hop to each destination Node-SID. What BIER does replicating the packet hop by hop to each destination Node-SID. BIER does not a
not allow is to llow the
indicate intermediate hops, or in terms of SR the ability to indicate a sequence indication of intermediate hops or, in terms of SR, the ability to indicate a se
of SID quence of SIDs
to reach the destination. This is what BIER-TE and its adjacency scoped BP enabl to reach the destination. On the other hand, BIER-TE and its adjacency-scoped BP
es.</t> s provide these capabilities.</t>
</section>
</section> <section anchor="ack" numbered="false" toc="default">
<!-- SR --> <name>Acknowledgements</name>
<t>The authors would like to thank <contact fullname="Greg Shepherd"/>, <c
ontact fullname="IJsbrand Wijnands"/>, <contact fullname="Neale Ranns"/>,
<contact fullname="Dirk Trossen"/>, <contact fullname="Sandy Zheng"/>, <contact
fullname="Lou Berger"/>, <contact fullname="Jeffrey Zhang"/>, <contact fullname=
"Carsten Bormann"/>, and <contact fullname="Wolfgang Braun"/> for their reviews
and suggestions.</t>
<t> Special thanks to <contact fullname="Xuesong Geng"/> for shepherding t
his document. Special thanks also for IESG review/suggestions by <contact fulln
ame="Alvaro Retana"/> (responsible AD/RTG), <contact fullname="Benjamin Kaduk"/>
(SEC), <contact fullname="Tommy Pauly"/> (TSV), <contact fullname="Zaheduzzaman
Sarker"/> (TSV), <contact fullname="Éric Vyncke"/> (INT), <contact fullname="Ma
rtin Vigoureux"/> (RTG), <contact fullname="Robert Wilton"/> (OPS), <contact ful
lname="Erik Kline"/> (INT), <contact fullname="Lars Eggert"/> (GEN), <contact fu
llname="Roman Danyliw"/> (SEC), <contact fullname="Ines Robles"/> (RTGDIR), <con
tact fullname="Robert Sparks"/> (Gen-ART), <contact fullname="Yingzhen Qu"/> (RT
GDIR), and <contact fullname="Martin Duke"/> (TSV).</t>
</section>
</back> </back>
</rfc> </rfc>
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