SPRING Working Group
Internet Engineering Task Force (IETF) W. Cheng, Ed.
Internet-Draft
Request for Comments: 9545 H. Li
Intended status:
Category: Standards Track China Mobile
Expires: 2 June 2024
ISSN: 2070-1721 C. Li, Ed.
Huawei Technologies
R. Gandhi
Cisco Systems, Inc.
R. Zigler
Broadcom
30 November 2023
February 2024
Path Segment Identifier in MPLS Based MPLS-Based Segment Routing Network
draft-ietf-spring-mpls-path-segment-22 Networks
Abstract
A Segment Routing (SR) path is identified by an SR segment list. A
sub-set
subset of segments from the segment list cannot be leveraged to
distinguish one SR path from another as they may be partially
congruent. SR path identification is a pre-requisite prerequisite for various
use-cases use
cases such as Performance Measurement, performance measurement and end-to-end 1+1 path
protection.
In an SR for over MPLS (SR-MPLS) data plane (SR-MPLS), plane, an Egress egress node cannot
determine on which SR path a packet traversed the network from the
label stack because the segment identifiers are removed from the
label stack as the packet transits the network.
This document defines a Path Segment Identifier(PSID) Identifier (PSID) to identify an
SR path on the egress node of the path.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of six months RFC 7841.
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This Internet-Draft will expire on 2 June 2024.
https://www.rfc-editor.org/info/rfc9545.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Abbreviations and Terms . . . . . . . . . . . . . . . . . 3
2. Path Segment . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Equal-Cost Multipath(ECMP) Multipath (ECMP) Considerations . . . . . . . . 5
3. Use cases . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Cases
3.1. PSID for Performance Measurement . . . . . . . . . . . . 6
3.2. PSID for Bidirectional SR Path . . . . . . . . . . . . . 7 Paths
3.3. PSID for End-to-end End-to-End Path Protection . . . . . . . . . . . 7
3.4. Nesting of PSIDs . . . . . . . . . . . . . . . . . . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 8
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 9
5.1. Huawei Technologies . . . . . . . . . . . . . . . . . . . 10
5.2. ZTE Corp . . . . . . . . . . . . . . . . . . . . . . . . 10
5.3. New H3C Technologies . . . . . . . . . . . . . . . . . . 11
5.4. Spirent Communications . . . . . . . . . . . . . . . . . 11
5.5. Fiberhome . . . . . . . . . . . . . . . . . . . . . . . . 12
5.6. Interoperability Test . . . . . . . . . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
7.
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1.
6.1. Normative References . . . . . . . . . . . . . . . . . . 13
7.2.
6.2. Informative References . . . . . . . . . . . . . . . . . 13
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 16
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
Segment Routing (SR) [RFC8402] leverages the source-routing paradigm
to steer packets from a source node through a controlled set of
instructions, called segments, "segments", by prepending the packet with an SR
header. In SR with the MPLS data plane SR-MPLS [RFC8660] [RFC8660], the SR header is
instantiated through a label stack.
In an SR-MPLS network, when a packet is transmitted along an SR path,
the labels in the MPLS label stack will be swapped or popped. The
result of this is that no label or only the last label may be left in
the MPLS label stack when the packet reaches the egress node. Thus,
the egress node cannot use the SR label stack to determine along
which SR path the packet came.
However, identifying a path on the egress node is a pre-requisite prerequisite for
various use-cases use cases in SR-MPLS networks, such as Performance
Measurement performance
measurement (Section 3.1), bidirectional path paths (Section 3.2), and end-
to-end
end-to-end 1+1 path protection (Live-Live (a Live-Live case) (Section 3.3).
Therefore, this document defines a new segment type, referred to
herein as a Path Segment. "Path Segment". A Path Segment is defined to uniquely
identify an SR path on the egress node of the path. It MAY be used
by the egress node for path identification. Note that, that per-path state
will be maintained in the egress node due to the requirements in the
aforementioned use cases, though in normal cases that cases, the per-
path per-path state
will be maintained in the ingress node only.
1.1. Requirements Language
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 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
1.2. Abbreviations and Terms
MPLS: Multiprotocol Label Switching.
SR: Switching
PSID: Path Segment Routing. Identifier
SID: Segment Identifier. Identifier
SR: Segment Routing
SR-MPLS: Instantiation of SR on the over MPLS data plane.
SR path: A SR path is a path described by a Segment-List. segment list.
Sub-Path: A sub-path is a part of a path, which contains a sub-set subset of the nodes and
links of the path.
PSID: Path Segment Identifier.
2. Path Segment
A Path Segment is a Local Segment local segment [RFC8402] which that uniquely identifies
an SR path on the egress node. A Path Segment Identifier(PSID) Identifier (PSID) is a
single label that is assigned from the Segment Routing Local Block
(SRLB) [RFC8402] of the egress node of an SR path.
A PSID is used to identify a Segment List. segment list. However, one PSID can be
used to identify multiple Segment Lists segment lists in some use cases if needed.
For example, one single PSID MAY be used to identify some or all
Segment
segment lists in a Candidate candidate path or an SR policy, policy if an operator
would like to aggregate these Segment Lists segment lists in operation.
When a PSID is used, the PSID can be inserted at the ingress node and
MUST immediately follow the last label of the SR path, path; in other
words, it must be inserted after the routing segment (adjacency/node/prefix (adjacency,
node, or prefix segment) that is pointing to the egress node of the
SR path. Therefore, a PSID will not be the top label in the label
stack when received on an intermediate node of the associated path,
but it can be the top label in the label stack on the penultimate
node.
The value of the TTL field in the MPLS label stack entry containing a
PSID can be set to any value except 0. If a PSID is the bottom
label, the S bit MUST be set, and if the PSID is NOT the bottom
label, the S bit MUST be 0.
The egress node MUST pop the PSID. The egress node MAY use the PSID
for further processing. For example, when performance measurement is
enabled on the SR path, it can trigger packet counting or
timestamping.
The addition of the PSID will require the egress to read and process
the PSID label in addition to the regular processing. This
additional processing may have an impact on forwarding performance.
Behavior relating to the use of explicit null directly preceding the
PSID is undefined in this document.
A Generic Associated Channel Label (GAL) MAY be used for Operations,
Administration
Administration, and Maintenance (OAM) in MPLS networks. As per
[RFC5586], when a GAL is used, the ACH Associated Channel Header (ACH)
appears immediately after the bottom of the label stack.
The SR path computation needs to know the Maximum SID Depth (MSD)
that can be imposed at the ingress node of a given SR path [RFC8664].
This ensures that the SID stack depth of a computed path does not
exceed the number of SIDs the node is capable of imposing. As per
[RFC8491]
[RFC8491], the MSD signals the total number of MPLS labels that can
be imposed, where the total number of MPLS labels includes the PSID.
An example label stack with a PSID is shown in Figure 1:
+--------------------+
| ... |
+--------------------+
| Label 1 |
+--------------------+
| Label 2 |
+--------------------+
| ... |
+--------------------+
| Label n |
+--------------------+
| PSID |
+--------------------+
~ Payload ~
+--------------------+
Figure 1: Label Stack with a PSID
Where:
* The Labels 1 to n are the segment label stack used to direct how
to steer the packets along the SR path.
* The PSID identifies the SR path in the context of the egress node
of the SR path.
Signaling
The signaling of the PSID between the egress node, the ingress node node,
and possibly a centralized controller is out of the scope of this
document.
2.1. Equal-Cost Multipath(ECMP) Multipath (ECMP) Considerations
If an Entropy Label(EL) Label (EL) is also used on the egress node, as per
[RFC6790]
[RFC6790], the Entropy label Indicator (ELI) EL and Entropy Label (EL) Indicator (ELI) would be placed
before the tunnel label and hence does label; hence, they do not interfere with the PSID PSID,
which is placed below.
It is worthy to note that in the case of ECMP, with or without the
use of an EL, the SR packets may be forwarded over multiple paths.
In this case, the SID list cannot directly reflect the actual
forwarding path and the PSID can only identify the SID list rather
than the actual forwarding path.
Also, similar to a Synonymous Flow Labels(SFL) Label (SFL) [RFC8957], the
introduction of an a PSID to an existing flow may cause that flow to
take a different path through the network under the conditions of Equal-
Cost Multipath. This, in
ECMP. In turn, this may invalidate certain uses of the PSID, such as
performance measurement applications. Therefore, the considerations
of SFLs as per section Section 5 in [RFC8957] of SFL [RFC8957] also apply to
PSID PSIDs in
implementation.
3. Use cases Cases
This section describes use cases which that can leverage the PSID. The
content is for informative purpose, purposes, and the detailed solutions might
be defined in other documents in the future.
3.1. PSID for Performance Measurement
As defined in [RFC7799], performance measurement can be classified
into Passive, Active, and Hybrid measurement. measurements. Since a PSID is
encoded in the SR-MPLS Label Stack label stack, as shown in Figure 1, existing
implementation
implementations on the egress node can leverage a PSID for measuring
packet counts.
For Passive performance measurement, path identification at the
measuring points is the pre-requisite. prerequisite. A PSID can be used by the
measuring points (e.g., the ingress and egress nodes of the SR path
or a centralized controller) to correlate the packet counts and
timestamps from the ingress and egress nodes for a specific SR path,
then path;
then, packet loss and delay can be calculated for the end-to-end
path, respectively.
Furthermore, a PSID can also be used for:
* Active Performance Measurement performance measurement for an SR path in SR-MPLS networks
for collecting packet counters and timestamps from the egress node
using probe messages.
* In-situ OAM[RFC9197] In situ OAM [RFC9197] for SR-MPLS to identify the SR Path path
associated with the in-situ in situ data fields in the data packets on the
egress node.
* In-band Performance Measurement performance measurement for SR-MPLS to identify the SR
Path
path associated with the collected performance metrics.
3.2. PSID for Bidirectional SR Path Paths
In some scenarios, for example, scenarios (e.g., mobile backhaul transport networks, networks), there
are requirements to support bidirectional paths[RFC6965], paths [RFC6965], and the
path is normally treated as a single entity. Forward and reverse
directions of the path have the same fate, fate; for example, failure in
one direction will result in switching traffic at both directions.
MPLS supports this by introducing the concepts of a co-routed
bidirectional LSP Label Switched Path (LSP) and an associated
bidirectional LSP [RFC5654].
In the current SR architecture, an SR path is a unidirectional path
[RFC8402]. In order to support bidirectional SR paths, a
straightforward way is to bind two unidirectional SR paths to a
single bidirectional SR path. PSIDs can be used to identify and
correlate the traffic for the two unidirectional SR paths at both
ends of the bidirectional path.
The mechanism of constructing bidirectional path paths using a PSID is out
of the scope of this document and has been described in several
documents, such as [I-D.ietf-pce-sr-bidir-path] [BIDIR-PATH] and
[I-D.ietf-idr-sr-policy-path-segment]. [SR-EXTENSIONS].
3.3. PSID for End-to-end End-to-End Path Protection
For end-to-end 1+1 path protection (i.e., a Live-Live case), the
egress node of the path needs to know the set of paths that
constitute the primary and the secondaries, secondaries in order to select the
primary path packets for onward transmission, transmission and to discard the
packets from the secondaries [RFC4426].
To do this in Segment Routing, SR, each SR path needs a path identifier that is unique
at the egress node. For SR-MPLS, this can be the Path Segment label
allocated by the egress node.
The detailed solution of using a PSID in end-to-end 1+1 path
protection is out of the scope of this document.
3.4. Nesting of PSIDs
A Binding SID (BSID) [RFC8402] can be used for SID list compression.
With a BSID, an end-to-end SR path in a trusted domain can be split
into several sub-paths, where each sub-path is identified by a BSID. Then
Then, an end-to-end SR path can be identified by a list of BSIDs, BSIDs;
therefore, it can provide better scalability.
A BSID and a PSID can be combined to achieve both sub-path and end-to-end end-
to-end path monitoring. A reference model for such a combination in
(Figure 2) shows an end-to-end path (A->D) in a trusted domain that
spans three subdomains (Access, Aggregation (the Access, Aggregation, and Core domain) domains)
and consists of three sub-paths, one in each subdomain (sub-path
(A->B), sub-path (B->C) (B->C), and sub-path (C->D)).
The SID list of a sub-path can be expressed as <SID1, SID2, ...SIDn, ...,
SIDn, s-PSID>, where the s-PSID is the PSID of the sub-path. Each
sub-path is associated with a BSID and an s-PSID.
The SID list of the end-to-end path can be expressed as <BSID1,
BSID2, ..., BSIDn, e-PSID>, where the e-PSID is the PSID of the end-
to-end path.
Figure 2 shows the details of the label stacks when a PSID and a BSID
are used to support both sub-path and end-to-end path monitoring in a
multi-domain scenario.
/--------\ /--------\ /--------\
/ \ / \ / \
A{ Access }B{ Aggregation }C{ Core }D
\ / \ / \ /
\--------/ \--------/ \--------/
Sub-path(A->B) Sub-path(B->C) Sub-path(C->D)
sub-path(A->B) sub-path(B->C) sub-path(C->D)
|<--------------->|<-------------->|<-------------->|
E2E Path(A->D)
|<------------------------------------------------->|
+------------+
+-------------+
~A->B SubPath~
+------------+ +------------+
|s-PSID(A->B)| sub-path~
+-------------+ +-------------+
|s-PSID(A->B) | ~B->C SubPath~
+------------+ +------------+ +------------+ sub-path~
+-------------+ +-------------+ +-------------+
| BSID(B->C) | |s-PSID(B->C)| |s-PSID(B->C) | ~C->D SubPath~
+------------+ +------------+ +------------+ sub-path~
+-------------+ +-------------+ +-------------+
| BSID(C->D) | | BSID(C->D) | |s-PSID(C->D)|
+------------+ +------------+ +------------+ |s-PSID(C->D) |
+-------------+ +-------------+ +-------------+ +------------+
|e-PSID(A->D) | |e-PSID(A->D) | |e-PSID(A->D) | |e-PSID(A->D)| |e-PSID(A->D)| |e-PSID(A->D)| |e-PSID(A->D)|
+------------+ +------------+ +------------+
+-------------+ +-------------+ +-------------+ +------------+
Figure 2: Nesting of PSIDs
4. Security Considerations
A PSID in SR-MPLS is a local label similar to other labels/Segment, labels and
segments, such as a VPN label, defined in MPLS and SR-MPLS. The data
plane processing of a PSID is a local implementation of an ingress node,
node or an egress node, which follows the same logic of an existing
MPLS
dataplane. data plane. As per the definition of a PSID, only the egress
node and the ingress node of the associated path will learn the
information of a PSID. The intermediate nodes of this path will not
learn it.
A PSID may be used on an ingress node that is not the ingress of the
associated path, path if the associated label stack with the PSID is part
of a deeper label stack which that represents a longer path. For example example,
the case described in Section 3.4 and the related BSID is are not used
while the original label stack of a sub-path is inserted as a part of
the whole label stack. In this case, the PSID must be distributed in
a trusted domain under the considerations defined in Section 8.1 of
[RFC8402].
A PSID is used within an SR-MPLS trusted domain [RFC8402] and must
not leak outside the domain, therefore domain; therefore, no new security threats are
introduced comparing compared to current SR-MPLS. As per [RFC8402], SR domain
boundary routers MUST filter any external traffic destined to a label
associated with a segment within the trusted domain, domain; this applies to
a PSID as well. Other security considerations of SR-MPLS, SR-MPLS described
in Section 8.1 of [RFC8402] applies apply to this document.
The distribution of a PSID from an egress node to an ingress nodes node is
performed within an SR trusted SR-trusted domain, and it is out of the scope of
this document. The details of the mechanism and related security
considerations will be described in other documents.
5. Implementation Status
[Note to the RFC Editor - remove this section before publication, as
well as remove the reference to [RFC7942].
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
5.1. Huawei Technologies
* Organization: Huawei Technologies.
* Implementation: Huawei PTN7900 Series Routers implementation of
SR-TP[HW-IMP].
* Description: SR-TP is a feature of Huawei PTN7900 series Routers,
which uses PSIDs to associate with paths and build up
bidirectional paths. Huawei PTN7900 Series Routers with version
V100R018C00 and above have commercially implemented the definition
of PSID and use cases which is defined in section 2 and
Section 3.2 in this document, including all the "MUST" and
"SHOULD" clauses, while other use cases for PSID in section 3 are
not yet implemented. For control plane, PTN7900 Series Routers
support configuring PSID using NETCONF.
* Maturity Level: Product
* Coverage: Partial, section 2 and use case section 3.2.
* Version: Draft-12
* Licensing: N/A
* Implementation experience: Nothing specific.
* Contact: li.fan@huawei.com
* Last updated: September 14, 2023
5.2. ZTE Corp
* Organization: ZTE Corporation.
* Implementation: ZTE's SPN implementation of PSID[ZTE-IMP].
* Description: The feature of SR-MPLS PSID has been implemented in
ZTE SPN products and follows the definition and mechanism as
defined in section 2 and Section 3.2 including all the "MUST" and
"SHOULD" clauses while other use cases for PSID in section 3 are
not yet implemented.
* Maturity Level: Product
* Coverage: Partial,section 2 and use case section 3.2.
* Version: Draft-12
* Licensing: N/A
* Implementation experience: Nothing specific.
* Contact: liu.aihua@zte.com.cn
* Last updated: September 21, 2023
5.3. New H3C Technologies
* Organization: New H3C Technologies.
* Implementation: H3C CR16000, CR19000 series routers implementation
of PSID.
* Description: Section 2 and Section 3.2 including all the "MUST"
and "SHOULD" clauses have been implemented in above-mentioned New
H3C Products(running Version 7.1.086 and above) for testing, while
other use cases for PSID in section 3 are not yet implemented.
* Maturity Level: Beta
* Coverage: Partial, section 2 and use case section 3.2.
* Version: Draft-12
* Licensing: N/A
* Implementation experience: Nothing specific.
* Contact: linchangwang.04414@h3c.com
* Last updated: September 13, 2023
5.4. Spirent Communications
* Organization: Spirent Communications
* Implementation: Spirent Testcenter Product Family implementation
of SR-TP test capability[SP-IMP].
* Description: Spirent Testcenter product family implements SR-MPLS
PSID test capabilities on the versions above Spirent Testcenter
4.85. Spirent Testcenter fully support testing all clauses
defined in section 2 and Section 3.1,3.2,3.4 , including all the
"MUST" and "SHOULD" clauses, and partially support the test of
clauses in section 3.3.
* Maturity Level: Production
* Coverage: fully cover section 2 and use case section 3.1,3.2, 3.4,
partially cover section 3.3
* Version: Draft-12
* Licensing: N/A
* Implementation experience: Nothing specific.
* Contact: junqi.zhao@spirent.com
* Last updated: September 21, 2023
5.5. Fiberhome
* Organization: Fiberhome Corporation.
* Implementation: Fiberhome SPN series of products (Citrans
650/690E) implementation of PSID[FH-IMP].
* Description: SR-TP is a feature of SPN products, which realizes a
controllable L3 tunnel, builds the end-to-end L3 deployment
business model. The PSID follows the definition and mechanism as
defined in section 2 and Section 3.2 including all the "MUST" and
"SHOULD" clauses had been implemented, while other use cases for
PSID in section 3 are not yet implemented.
* Maturity Level: Product
* Coverage: Partial,section 2 and use case section 3.2.
* Version: Draft-12
* Licensing: N/A
* Implementation experience: Nothing specific.
* Contact: zhhan@fiberhome.com
* Last updated: September 21, 2023
5.6. Interoperability Test
[Note to the RFC Editor - remove this section before publication, as
well as remove the reference to [RFC7942].
The Interoperability test of PSID had been done among products from
several vendors, including Huawei(PTN7900, V100R018C00), ZTE(ZXCTN
6180, Ver 4.00.00), FiberHome(Citrans 650/690E) , Spirent (Chassis:
SPT-N4U-220.Test. Module: PX3-QSFP28-12-225A. Version: 4.86) and
Nokia in 2018[INTEROP-TEST]. Note that PSID is a key feature of
Layer3 in SPN architecture [SPN-L3]. This is reported by Weiqiang
Cheng from China Mobile at September, 21, 2023.
6. IANA Considerations
This document does not require any has no IANA actions.
7.
6. References
7.1.
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>. <https://www.rfc-editor.org/info/rfc8174>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/rfc/rfc8402>. <https://www.rfc-editor.org/info/rfc8402>.
[RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC8660, December 2019,
<https://www.rfc-editor.org/rfc/rfc8660>.
7.2.
<https://www.rfc-editor.org/info/rfc8660>.
6.2. Informative References
[FH-IMP] "Fiberhome Routers", 21 September 2021,
<https://www.fiberhome.com/operator/product/
products/294.aspx.html>.
[HW-IMP] "Huawei PTN7900 Routers", 21 September 2021,
<https://carrier.huawei.com/en/products/fixed-network/
carrier-ip/router/ptn/ptn7900>.
[I-D.ietf-idr-sr-policy-path-segment]
Li, C., Li, Z., Yin, Y., Cheng, W., and K. Talaulikar, "SR
Policy Extensions for Path Segment and Bidirectional
Path", Work in Progress, Internet-Draft, draft-ietf-idr-
sr-policy-path-segment-08, 16 August 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-sr-
policy-path-segment-08>.
[I-D.ietf-pce-sr-bidir-path]
[BIDIR-PATH]
Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong,
"Path Computation Element Communication Protocol (PCEP)
Extensions for Associated Bidirectional Segment Routing
(SR) Paths", Work in Progress, Internet-Draft, draft-ietf-
pce-sr-bidir-path-12, 9 September 2023,
pce-sr-bidir-path-13, 13 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-sr-
bidir-path-12>.
[INTEROP-TEST]
China Mobile, "Adhering to Innovation-Driven Development
and Focusing on Technological Breakthroughs--China Mobile
Research Institute Accelerates 5G R&D and Tests", 30 May
2019, <http://www.cww.net.cn/web/news/channel/
articleinfo.action?id=452789>.
bidir-path-13>.
[RFC4426] Lang, J., Ed., Rajagopalan, B., Ed., and D. Papadimitriou,
Ed., "Generalized Multi-Protocol Label Switching (GMPLS)
Recovery Functional Specification", RFC 4426,
DOI 10.17487/RFC4426, March 2006,
<https://www.rfc-editor.org/rfc/rfc4426>.
<https://www.rfc-editor.org/info/rfc4426>.
[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
"MPLS Generic Associated Channel", RFC 5586,
DOI 10.17487/RFC5586, June 2009,
<https://www.rfc-editor.org/rfc/rfc5586>.
<https://www.rfc-editor.org/info/rfc5586>.
[RFC5654] Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
Sprecher, N., and S. Ueno, "Requirements of an MPLS
Transport Profile", RFC 5654, DOI 10.17487/RFC5654,
September 2009, <https://www.rfc-editor.org/rfc/rfc5654>. <https://www.rfc-editor.org/info/rfc5654>.
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/rfc/rfc6790>.
<https://www.rfc-editor.org/info/rfc6790>.
[RFC6965] Fang, L., Ed., Bitar, N., Zhang, R., Daikoku, M., and P.
Pan, "MPLS Transport Profile (MPLS-TP) Applicability: Use
Cases and Design", RFC 6965, DOI 10.17487/RFC6965, August
2013, <https://www.rfc-editor.org/rfc/rfc6965>. <https://www.rfc-editor.org/info/rfc6965>.
[RFC7799] Morton, A., "Active and Passive Metrics and Methods (with
Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
May 2016, <https://www.rfc-editor.org/rfc/rfc7799>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/rfc/rfc7942>. <https://www.rfc-editor.org/info/rfc7799>.
[RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
DOI 10.17487/RFC8491, November 2018,
<https://www.rfc-editor.org/rfc/rfc8491>.
<https://www.rfc-editor.org/info/rfc8491>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/rfc/rfc8664>.
<https://www.rfc-editor.org/info/rfc8664>.
[RFC8957] Bryant, S., Chen, M., Swallow, G., Sivabalan, S., and G.
Mirsky, "Synonymous Flow Label Framework", RFC 8957,
DOI 10.17487/RFC8957, January 2021,
<https://www.rfc-editor.org/rfc/rfc8957>.
<https://www.rfc-editor.org/info/rfc8957>.
[RFC9197] Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi,
Ed., "Data Fields for In Situ Operations, Administration,
and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197,
May 2022, <https://www.rfc-editor.org/rfc/rfc9197>.
[SP-IMP] "Spirent Devices", 21 September 2021,
<https://www.spirent.com/assets/u/flexe-test-solution-for-
5g-backhaul>.
[SPN-L3] China Mobile, "The-transport-network-consi-deration-for-
5G-in-CMCC", 1 December 2018, <https://opennetworking.org/
wp-content/uploads/2018/12/The-transport-network-consi-
deration-for-5G-in-CMCC.pdf>.
[ZTE-IMP] "ZTE ZXCTN-6700 Routers", 21 September 2021,
<https://www.zte.com.cn/china/product_index/ip_network/
item01/zxctn-6700/zxctn_6700.html>. <https://www.rfc-editor.org/info/rfc9197>.
[SR-EXTENSIONS]
Li, C., Li, Z., Yin, Y., Cheng, W., and K. Talaulikar, "SR
Policy Extensions for Path Segment and Bidirectional
Path", Work in Progress, Internet-Draft, draft-ietf-idr-
sr-policy-path-segment-08, 16 August 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-sr-
policy-path-segment-08>.
Acknowledgements
The authors would like to thank Adrian Farrel, Stewart Bryant,
Shuangping Zhan, Alexander Vainshtein, Andrew G. Malis, Ketan
Talaulikar, Shraddha Hegde, Xinyue Zhang, Loa Andersson Andersson, and Bruno
Decraene for their review, suggestions, comments comments, and contributions
to this document.
The authors would like to acknowledge the contribution from Alexander
Vainshtein on "Nesting of PSIDs". PSIDs" (Section 3.4).
Contributors
The following people have substantially contributed to this document.
Mach(Guoyi) Chen
Huawei Technologies Co., Ltd Ltd.
Email: mach.chen@huawei.com
Lei Wang
China Mobile
Email: wangleiyj@chinamobile.com
Aihua Liu
ZTE Corp Corp.
Email: liu.aihua@zte.com.cn
Greg Mirsky
ZTE Corp Corp.
Email: gregimirsky@gmail.com
Gyan S. Mishra
Verizon Inc.
Email: gyan.s.mishra@verizon.com
Authors' Addresses
Weiqiang Cheng (editor)
China Mobile
Email: chengweiqiang@chinamobile.com
Han Li
China Mobile
Email: lihan@chinamobile.com
Cheng Li (editor)
Huawei Technologies
China
Email: c.l@huawei.com
Rakesh Gandhi
Cisco Systems, Inc.
Canada
Email: rgandhi@cisco.com
Royi Zigler
Broadcom
Email: royi.zigler@broadcom.com