wdiff rfc7140.original rfc7140.txt

Network Working Group
Internet Engineering Task Force (IETF) L. Jin
Internet-Draft
Intended status:
Request for Comments: 7140
Category: Standards Track F. Jounay
Expires: July 2, 2014 France Telecom
I.
ISSN: 2070-1721 Orange CH
IJ. Wijnands
Cisco Systems, Inc
N. Leymann
Deutsche Telekom AG
December 29, 2013
February 2014

LDP Extensions for Hub & and Spoke Multipoint Label Switched Path
draft-ietf-mpls-mldp-hsmp-06.txt

Abstract

This draft document introduces a hub & and spoke multipoint (HSMP) Label
Switched Path (LSP), which allows traffic both from root to leaf through
point-to-multipoint (P2MP) LSP LSPs and also leaf to root along the
reverse path. That means traffic entering the HSMP LSP from the
application/customer at the root node travels downstream to each leaf
node, exactly as if it is travelling were traveling downstream along a P2MP LSP to
each leaf node. Upstream traffic entering the HSMP LSP at any leaf
node travels upstream along the tree to the root, as if it is were
unicast to the root. Direct communication among the leaf nodes is
not allowed.

Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [RFC2119].

Status of this This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of six months this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 2, 2014.
http://www.rfc-editor.org/info/rfc7140.

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Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3
3. Setting up Up HSMP LSP with LDP . . . . . . . . . . . . . . . . . 5 4
3.1. Support for HSMP LSP Setup with LDP . . . . . . . . . . . 5 4
3.2. HSMP FEC Elements . . . . . . . . . . . . . . . . . . . . 6 5
3.3. Using the HSMP FEC Elements . . . . . . . . . . . . . . . 6 5
3.4. HSMP LSP Label Map . . . . . . . . . . . . . . . . . . . . 7 6
3.4.1. HSMP LSP Leaf Node Operation . . . . . . . . . . . . . 8 7
3.4.2. HSMP LSP Transit Node Operation . . . . . . . . . . . 8 7
3.4.3. HSMP LSP Root Node Operation . . . . . . . . . . . . . 9 8
3.5. HSMP LSP Label Withdraw . . . . . . . . . . . . . . . . . 10 9
3.5.1. HSMP Leaf Operation . . . . . . . . . . . . . . . . . 10 9
3.5.2. HSMP Transit Node Operation . . . . . . . . . . . . . 10 9
3.5.3. HSMP Root Node Operation . . . . . . . . . . . . . . . 10
3.6. HSMP LSP Upstream LSR Change . . . . . . . . . . . . . . . 11 10
3.7. Determining Forwarding Interface . . . . . . . . . . . . . 11 10
4. HSMP LSP on a LAN . . . . . . . . . . . . . . . . . . . . . . 11
5. Redundancy Considerations . . . . . . . . . . . . . . . . . . 12 11
6. Failure Detection of HSMP LSP . . . . . . . . . . . . . . . . 12 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 12
8.1. New LDP FEC Element types Types . . . . . . . . . . . . . . . . 13 12
8.2. HSMP LSP capability Capability TLV . . . . . . . . . . . . . . . . . 13
8.3. New sub-TLVs Sub-TLVs for the Target Stack TLV . . . . . . . . . . 14 13
9. Acknowledgement Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Normative references . References . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 14

1. Introduction

The point-to-multipoint (P2MP) Label Switched Path (LSP) defined in
[RFC6388] allows traffic to transmit from root to several leaf nodes,
and multipoint-to-multipoint (MP2MP) LSP allows traffic from every
node to transmit to every other node. This draft document introduces a hub &
and spoke multipoint (HSMP) LSP, which has one root node and one or
more leaf nodes. An HSMP LSP allows traffic both from root to leaf
through downstream LSP and also leaf to root along the upstream LSP.
That means traffic entering the HSMP LSP at the root node travels
along the downstream LSP, exactly as if it is travelling were traveling along a
P2MP LSP, and traffic entering the HSMP LSP at any other leaf nodes
travels along the upstream LSP toward only the root node. The
upstream LSP should be thought of as a unicast LSP to the root node,
except that it follows the reverse direction of the downstream LSP,
rather than routing protocol
based the unicast path. path based on the routing protocol. The
combination of upstream LSPs initiated from all leaf nodes forms a
multipoint-to-point LSP.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

This document uses some the following terms and acronyms as follows: acronyms:

mLDP: Multipoint extensions for Label Distribution Protocol (LDP)
defined in [RFC6388].

P2MP LSP: point-to-multipoint Label Switched Path. An LSP that
has one Ingress Label Switching Router (LSR) and one or more
Egress LSRs.

MP2MP LSP: multipoint-to-multipoint Label Switched Path. An LSP
that connects a set of nodes, such that traffic sent by any node
in the LSP is delivered to all others.

HSMP LSP: hub & and spoke multipoint Label Switched Path. An LSP
that has one root node and one or more leaf nodes, allows traffic
from the root to all leaf nodes along the downstream P2MP LSP and
also leaf to root node along the upstream unicast LSP.

FEC: Forwarding Equivalence Class

3. Setting up Up HSMP LSP with LDP

An HSMP LSP is similar to MP2MP LSP described in [RFC6388], with the
difference being that, when the leaf LSRs send traffic on the LSP,
the traffic is first delivered only to the root node and follows the
upstream path from the leaf node to the root node. The root node
then distributes the traffic on the P2MP tree to all of the leaf
nodes.

An HSMP LSP consists of a downstream path and upstream path. The
downstream path is the same as P2MP LSP, while the upstream path is
only from leaf to root node, without communication between the leaf and leaf
nodes.
nodes themselves. The transmission of packets from the root node of
an HSMP LSP to the receivers (the leaf nodes) is identical to that of
a P2MP LSP. Traffic from a leaf node to the root follows the
upstream path that is the reverse of the path from the root to the
leaf. Unlike an MP2MP LSP, traffic from a leaf node does not branch
toward other leaf nodes, but it is sent direct to the root where it
is placed on the P2MP path and distributed to all leaf nodes
including the original sender.

To set up the upstream path of an HSMP LSP, ordered mode MUST be
used. Ordered mode can guarantee that a leaf to will start sending
packets to the root immediately after the upstream path is installed,
without being dropped due to an incomplete LSP.

3.1. Support for HSMP LSP Setup with LDP

An HSMP LSP requires the LDP capabilities [RFC5561] for nodes to
indicate that they support setup of HSMP LSPs. An implementation
supporting the HSMP LSP procedures specified in this document MUST
implement the procedures for Capability Parameters in Initialization
Messages.
messages. Advertisement of the HSMP LSP Capability indicates support
of the procedures for HSMP LSP setup.

A new Capability Parameter TLV is defined, the HSMP LSP Capability
Parameter. Following Below is the format of the HSMP LSP Capability Parameter.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| HSMP LSP Cap(TBD IANA) Cap (0x0902) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Reserved |
+-+-+-+-+-+-+-+-+

Figure 1. 1: HSMP LSP Capability Parameter encoding Encoding
U-bit: Unknown TLV bit, as described in [RFC5036]. The value MUST
be 1. The unknown TLV MUST be silently ignored and the rest
of the message processed as if the unknown TLV did not exist.

F-bit: Forward unknown TLV bit, as described in [RFC5036]. The
value of this bit MUST be 0 since a Capability Parameter TLV
is sent only in Initialization and Capability messages, which
are not forwarded.

The length

Length: SHOULD be 1, and the S bit and reserved bits are 1.

S-bit: As defined in [RFC5561] section 3.

The Section 3 of [RFC5561].

Reserved: As defined in Section 3 of [RFC5561].

HSMP LSP Capability Parameter type is to be assigned by IANA. type: 0x0902.

If the peer has not advertised the corresponding capability, then
label messages using the HSMP Forwarding Equivalence Class (FEC)
Element SHOULD NOT (as described in [RFC6388] section 2.1) be sent to the peer. peer (as described in Section 2.1
of [RFC6388]). Since ordered mode is applied for HSMP LSP signalling, signaling,
the label message break would ensure that the initiating leaf node is
unable to establish the upstream path to root node.

3.2. HSMP FEC Elements

Similar as MP2MP LSP, we

We define two new protocol entities, entities: the HSMP Downstream FEC Element
and Upstream FEC Element. If a FEC TLV contains one of the HSMP FEC
Elements, the HSMP FEC Element MUST be the only FEC Element in the
FEC TLV. The structure, encoding encoding, and error handling for the HSMP Downstream HSMP-
downstream FEC Element and Upstream HSMP-upstream FEC Element are the same as
for the P2MP FEC Element described in
[RFC6388] Section 2.2. 2.2 of [RFC6388]. The
difference is that two additional new FEC types are defined: HSMP Downstream HSMP-
downstream FEC (to be assigned by IANA) (10) and
HSMP Upstream HSMP-upstream FEC (to be assigned by IANA). (9).

3.3. Using the HSMP FEC Elements

In order to describe the message processing clearly, the

The entries in the list below define describe the processing of the HSMP FEC
Elements. Additionally, the entries defined in [RFC6388] section Section 3.3 of
[RFC6388] are also reused in the following sections.

1. HSMP downstream LSP <X, Y> (or simply downstream <X, Y>): an
HSMP LSP downstream path with root node address X and opaque
value Y.

2. HSMP upstream LSP <X, Y> (or simply upstream <X, Y>): an HSMP
LSP upstream path for root node address X and opaque value Y which
that will be used by any of downstream node to send traffic
upstream to root node.

3. HSMP downstream HSMP-downstream FEC Element <X, Y>: a FEC Element with root node
address X and opaque value Y used for a downstream HSMP LSP.

4. HSMP upstream HSMP-upstream FEC Element <X, Y>: a FEC Element with root node
address X and opaque value Y used for an upstream HSMP LSP.

5. HSMP-D Label Mapping <X, Y, L>: A Label Mapping message with a
single HSMP downstream HSMP-downstream FEC Element <X, Y> and label TLV with
label L. Label L MUST be allocated from the per-platform label
space of the LSR sending the Label Mapping Message.

6. HSMP-U Label Mapping <X, Y, Lu>: A Label Mapping message with a
single HSMP upstream FEC Element <X, Y> and label TLV with label
Lu. Label Lu MUST be allocated from the per-platform label
space of the LSR sending the Label Mapping Message.

7. HSMP-D Label Withdraw <X, Y, L>: a Label Withdraw message with a
FEC TLV with a single HSMP downstream HSMP-downstream FEC Element <X, Y> and
label TLV with label L.

8. HSMP-U Label Withdraw <X, Y, Lu>: a Label Withdraw message with
a FEC TLV with a single HSMP upstream HSMP-upstream FEC Element <X, Y> and
label TLV with label Lu.

9. HSMP-D Label Release <X, Y, L>: a Label Release message with a
FEC TLV with a single HSMP downstream HSMP-downstream FEC Element <X, Y> and
Label TLV with label L.

10. HSMP-U Label Release <X, Y, Lu>: a Label Release message with a
FEC TLV with a single HSMP upstream HSMP-upstream FEC Element <X, Y> and label
TLV with label Lu.

3.4. HSMP LSP Label Map

This section specifies the procedures for originating HSMP Label
Mapping messages and processing received HSMP Label Mapping messages
for a particular HSMP LSP. The procedure of a downstream HSMP LSP is
similar as to that of a downstream MP2MP LSP described in [RFC6388].
When LDP operates in Ordered Label Distribution Control mode
[RFC5036], the upstream LSP will be set up by sending an HSMP LSP LDP
Label Mapping message with a label which that is allocated by the upstream
LSR to its downstream LSR hop by hop hop-by-hop from root to leaf node,
installing the upstream forwarding table by every node along the LSP.

The detail detailed procedure of setting up upstream HSMP LSP is different with
than that of upstream MP2MP LSP, and it is specified in below the remainder
of this section.

All labels discussed here are downstream-assigned [RFC5332] except
those which that are assigned using the procedures described in Section 4.

Determining the upstream LSR for the HSMP LSP <X, Y> follows the
procedure for a P2MP LSP described in [RFC6388] Section 2.4.1.1. 2.4.1.1 of [RFC6388].
That is, a node Z that wants to join an HSMP LSP <X, Y> determines
the LDP peer U that is Z's next-hop next hop on the best path from Z to the
root node X. If there are multiple upstream LSRs, a local algorithm
should be applied to ensure that there is a single exactly one upstream LSRs LSR
for a particular LSP.

To determining determine one's HSMP downstream LSR, an upstream LDP peer which that
receives a Label Mapping with HSMP downstream the HSMP-downstream FEC Element from an
LDP peer D will treat D as HSMP downstream LDP peer.

3.4.1. HSMP LSP Leaf Node Operation

The leaf node operation is much the same as the operation of MP2MP
LSP defined in [RFC6388] Section 3.3.1.4. 3.3.1.4 of [RFC6388]. The only difference is
the FEC elements as specified below.

A leaf node Z of an HSMP LSP <X, Y> determines its upstream LSR U for
<X, Y> as per Section 3.3, allocates a label L, and sends an HSMP-D
Label Mapping <X, Y, L> to U. Leaf node Z expects an HSMP-U Label
Mapping <X, Y, Lu> from node U and checks whether it already has
forwarding state for upstream <X, Y>. If not, Z creates forwarding
state to push label Lu onto the traffic that Z wants to forward over
the HSMP LSP. How it determines what traffic to forward on this HSMP
LSP is outside the scope of this document.

3.4.2. HSMP LSP Transit Node Operation

The procedure of for processing an HSMP-D Label Mapping message is much
the same as
processing that for an MP2MP-D Label Mapping message defined in [RFC6388]
Section
3.3.1.5. 3.3.1.5 of [RFC6388]. The processing of an HSMP-U Label
Mapping message is different
with from that of an MP2MP-U Label Mapping
message as specified below.

Suppose node Z receives an HSMP-D Label Mapping <X, Y, L> from LSR D.
Z checks whether it has forwarding state for downstream <X, Y>. If
not, Z determines its upstream LSR U for <X, Y> as per Section 3.3.
Using this Label Mapping to update the label forwarding table MUST
NOT be done as long as LSR D is equal to LSR U. If LSR U is
different from LSR D, Z will allocate a label L' and install
downstream forwarding state to swap label L' with label L over
interface I associated with LSR D and send an HSMP-D Label Mapping
<X, Y, L'> to U. Interface I is determined via the procedures in
Section 3.7.

If Z already has forwarding state for downstream <X, Y>, all that Z
needs to do in this case is check that LSR D is not equal to the
upstream LSR of <X, Y> and update its forwarding state. Assuming its
old forwarding state was L'-> {<I1, L1> <I2, L2> ..., <In, Ln>}, its
new forwarding state becomes L'-> {<I1, L1> <I2, L2> ..., <In, Ln>,
<I, L>}. If the LSR D is equal to the installed upstream LSR, the
Label Mapping from LSR D MUST be retained and MUST NOT update the
label forwarding table.

Node Z checks if the upstream LSR U already has assigned a label Lu
to upstream <X, Y>. If not, transit node Z waits until it receives
an HSMP-U Label Mapping <X, Y, Lu> from LSR U. Once the HSMP-U Label
Mapping is received from LSR U, node Z checks whether it already has
forwarding state upstream <X, Y> with incoming label Lu' and outgoing
label Lu. If it does not, it allocates a label Lu' and creates a new
label swap for Lu' with Label Lu over interface Iu. Interface Iu is
determined via the procedures in Section 3.7. Node Z determines the
downstream HSMP LSR as per Section 4.3.1, 3.4 and sends an HSMP-U Label
Mapping <X, Y, Lu'> to node D.

Since a packet from any downstream node is forwarded only to the
upstream node, the same label (representing the upstream path) SHOULD
be distributed to all downstream nodes. This differs from the
procedures for MP2MP LSPs [RFC6388], where a distinct label must be
distributed to each downstream node. The forwarding state upstream
<X, Y> on node Z will be like this this: {<Lu'>, <Iu Lu>}. Iu means the
upstream interface over which Z receives HSMP-U Label Map <X, Y, Lu>
from LSR U. Packets from any downstream interface over which Z sends
HSMP-U Label Map <X, Y, Lu'> with label Lu' will be forwarded to Iu
with label Lu' swap swapped to Lu.

3.4.3. HSMP LSP Root Node Operation

The procedure of for an HSMP-D Label Mapping message is much the same as
processing an MP2MP-D Label Mapping message defined in [RFC6388]
Section
3.3.1.6. 3.3.1.6 of [RFC6388]. The processing of an HSMP-U Label
Mapping message is different
with from that of an MP2MP-U Label Mapping
message as specified below.

Suppose the root node Z receives an HSMP-D Label Mapping <X, Y, L>
from node D. Z checks whether it already has forwarding state for
downstream <X, Y>. If not, Z creates downstream forwarding state and
installs a an outgoing label L over interface I. Interface I is
determined via the procedures in Section 3.7. If Z already has
forwarding state for downstream <X, Y>, then Z will add label L over
interface I to the existing state.

Node Z checks if it has forwarding state for upstream <X, Y>. If
not, Z creates a forwarding state for incoming label Lu' that
indicates that Z is the HSMP LSP egress LER. E.g., Label Edge Router (LER). For
example, the forwarding state might specify that the label stack is
popped and the packet passed to some specific application. Node Z
determines the downstream HSMP LSR as per Section 3.3, 3.3 and sends an
HSMP-U Label Map <X, Y, Lu'> to node D.

Since Z is the root of the tree, Z will not send an HSMP-D Label Map
and will not receive an HSMP-U Label Mapping.

Root

The root node could also be a leaf node, and it is able to determine
what traffic to forward on this HSMP LSP which LSP; that determination is
outside the scope of this document.

3.5. HSMP LSP Label Withdraw

3.5.1. HSMP Leaf Operation

If a leaf node Z discovers that it has no need to be an Egress LSR
for that LSP (by means outside the scope of this document), then it
SHOULD send an HSMP-D Label Withdraw <X, Y, L> to its upstream LSR U
for <X, Y>, where L is the label it had previously advertised to U
for <X,Y>. <X, Y>. Leaf node Z will also send an unsolicited HSMP-U Label
Release <X, Y, Lu> to U to indicate that the upstream path is no
longer used and that label Lu can be removed.

Leaf node Z expects the upstream router U to respond by sending a
downstream Label Release for L.

3.5.2. HSMP Transit Node Operation

If a transit node Z receives an HSMP-D Label Withdraw message
<X, Y, L> from node D, it deletes label L from its forwarding state
downstream <X, Y>. Node Z sends an HSMP-D Label Release message with
label L to D. There is no need to send an HSMP-U Label Withdraw <X,
Y, Lu> to D because node D already removed Lu and sent a label
release for Lu to Z.

If deleting L from Z's forwarding state for downstream <X, Y> results
in no state remaining for <X, Y>, then Z propagates the HSMP-D Label
Withdraw <X, Y, L> to its upstream node U for <X, Y>. Z should also
check if there are any incoming interface interfaces in forwarding state
upstream <X, Y>. If all downstream nodes are released and there is
no incoming interface, Z should delete the forwarding state upstream
<X, Y> and send an HSMP-U Label Release message to its upstream node.
Otherwise, no HSMP-U Label Release message will be sent to the
upstream node.

3.5.3. HSMP Root Node Operation

When the root node of an HSMP LSP receives an HSMP-D Label Withdraw
message and an HSMP-U Label Release message, the procedure is the
same as that for transit nodes, except that the root node will not
propagate the Label Withdraw and Label Release upstream (as it has no
upstream).

3.6. HSMP LSP Upstream LSR Change

The procedure for changing the upstream LSR is the same as defined in
[RFC6388]
Section 2.4.3, 2.4.3 of [RFC6388], only with different processing of the FEC
Element.

When the upstream LSR changes from U to U', node Z should set up the
HSMP LSP <X, Y> to U' by applying the procedures in Section 3.4. Z
will also remove the HSMP LSP <X, Y> to U by applying the procedure
in Section 3.5.

To set up an HSMP LSP to U' before/after removing the HSMP LSP to U
is a local matter, and the matter. The recommended default behavior is to remove
before adding.

3.7. Determining Forwarding Interface

The co-routed path between upstream and downstream LSP would LSPs can be
achieved for HSMP LSP. co-routed by applying the
procedures below. Both LSR U and LSR D would ensure that the same
interface to send sends traffic by applying some procedures. For a network
with symmetric IGP cost configuration, the following procedure MAY be
used. To determine the downstream interface, LSR U MUST do a lookup
in the unicast routing table to find the best interface and next-hop next hop
to reach LSR D. If the next-hop next hop and interface are also advertised by
LSR D via the LDP session, it should be used to transmit the packet
to LSR D. Determine The mechanism to determine the upstream interface mechanism is the
same as
determining that used to determine the downstream interface by exchanging except the role
roles of LSR U and LSR D. D are switched. If symmetric IGP cost could
not be ensured, static route configuration on LSR U and D could also
be a possible way to ensure a co-routed path.

If a co-routed path is not required for the HSMP LSP, the procedure
defined in
[RFC6388] Section 2.4.1.2 of [RFC6388] could be applied. LSR U is
free to transmit the packet on any of the interfaces to LSR D. The
algorithm it uses to choose a particular interface is a local matter.
Determine

The mechanism to determine the upstream interface mechanism is the same as determining that
used to determine the downstream interface.

4. HSMP LSP on a LAN

The procedure to process the downstream HSMP LSP on a LAN is much the
same as for a downstream MP2MP LSP as described in [RFC6388] section 6.1.1. Section 6.1.1 of
[RFC6388].

When establishing the downstream path of an HSMP LSP, as defined in
[RFC6389], a Label Request message for an LSP label is sent to the
upstream LSR. The upstream LSR should send a Label Mapping message
that contains the LSP label for the downstream HSMP FEC and the
upstream LSR context label defined in [RFC5331]. When the LSR
forwards a packet downstream on one of those LSPs, the packet's top
label must be the "upstream LSR context label", label" and the packet's
second label is the "LSP label". The HSMP downstream path will be
installed in the context-specific forwarding table corresponding to
the upstream LSR label. Packets sent by the upstream LSR can be
forwarded downstream using this forwarding state based on a two-label
lookup.

The upstream path of an HSMP LSP on a LAN is the same as the one on
other kind kinds of links. That is, the upstream LSR must send a Label
Mapping message that contains the LSP label for the upstream HSMP FEC
to the downstream node. Packets travelling traveling upstream need to be
forwarded in the direction of the root by using the label allocated
for the upstream HSMP FEC.

5. Redundancy Considerations

In some scenarios, it is necessary to provide two root nodes for
redundancy purpose. purposes. One way to implement this is to use two
independent HSMP LSPs acting as active/standby. active and standby. At one a given time,
only one HSMP LSP will be active, and active; the other will be standby. After
detecting the failure of the active HSMP LSP, the root and leaf nodes
will switch the traffic to the standby HSMP LSP LSP, which takes on the
role as active HSMP LSP. The detail details of the redundancy mechanism is are
out of the scope. scope of this document.

6. Failure Detection of HSMP LSP

The idea of LSP ping for HSMP LSPs could be expressed as an intention
to test the LSP Ping Echo Request packets that enter at the root
along a particular downstream path of HSMP LSP, LSP and that end their
MPLS path on the leaf. The leaf node then sends the LSP Ping Echo
Reply along the upstream path of HSMP LSP, and end it ends on the root
that are is the (intended) root node.

New sub-TLVs are required to be have been assigned by IANA in Target FEC Stack TLV and
Reverse-path Target FEC Stack TLV to define the corresponding
HSMP-downstream HSMP-
downstream FEC type and HSMP-upstream FEC type. In order to ensure
that the leaf node to send sends the LSP Ping Echo Reply along the HSMP
upstream path, the R bit flag (Validate Reverse Path) in the Global Flags
Field
field defined in [RFC6426] is reused here.

The node processing node-processing mechanism of LSP Ping Echo Request and Echo Reply
for the HSMP LSP is inherited from [RFC6425] and [RFC6426] Section 3.4, 3.4 of
[RFC6426], except for the following:

1. The root node sending the LSP Ping Echo Request message for the
HSMP LSP MUST attach the Target FEC Stack TLV with HSMP the HSMP-
downstream FEC, FEC type, and set the R bit flag to '1' in the Global
Flags Field. field.

2. When the leaf node receiving receives the LSP Ping Echo Request, it MUST
send the LSP Ping Echo Reply to the associated HSMP upstream
path. The Reverse-path Target FEC Stack TLV attached by the leaf
node in the Echo Reply message SHOULD contain the sub-TLV of the
associated HSMP upstream HSMP-upstream FEC.

7. Security Considerations

The same security considerations apply as for the MP2MP LSP described
in [RFC6388] and [RFC6425].

Although this document introduces new FEC Elements and corresponding
procedures, the protocol does not bring any new security issues
compared to
beyond those in [RFC6388] and [RFC6425].

8. IANA Considerations

8.1. New LDP FEC Element types

This document requires allocation of two Types

Two new LDP FEC Element types have been allocated from the "Label
Distribution Protocol (LDP) Parameters registry" the Parameters" registry, under "Forwarding
Equivalence Class (FEC) Type Name Space":

1. the HSMP-upstream FEC type - requested value TBD 9

2. the HSMP-downstream FEC type - requested value TBD 10

The values should be have been allocated using the lowest free values from the "IETF Consensus"-range Consensus" [RFC5226]
range (0-127).

8.2. HSMP LSP capability Capability TLV

This document requires allocation of one

One new code points point has been allocated for the HSMP LSP capability TLV
from "Label Distribution Protocol (LDP) Parameters
registry" the Parameters" registry, under
"TLV Type Name Space":

HSMP LSP Capability Parameter - requested value TBD 0x0902

The value should be has been allocated from the the"IETF Consensus" range 0x0901-0x3DFF (IETF
Consensus) using the first free value within this range.
(0x0901-0x3DFF).

8.3. New sub-TLVs Sub-TLVs for the Target Stack TLV

This document requires allocation of two

Two new sub-TLV types have been allocated for inclusion within the
LSP ping [RFC4379] Target FEC Stack TLV (TLV type 1) and 1), Reverse-path
Target FEC Stack TLV (TLV type 16).

1. 16), and Reply Path TLV (TLV type 21).

o the HSMP-upstream LDP FEC Stack - requested value TBD

2. 29

o the HSMP-downstream LDP FEC Stack - requested value TBD 30

The value should be has been allocated from the IETF "IETF Standards Action Action" range
(0-16383) that is used for mandatory and optional sub-TLVs that
requires a response if not understood. The value should be allocated
using the lowest free value within this range.

9. Acknowledgement Acknowledgements

The author would like to thank Eric Rosen, Sebastien Jobert, Fei Su,
Edward, Mach Chen, Thomas Morin, and Loa Andersson for their valuable
comments.

10. References

10.1. Normative references References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC5331] Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
Label Assignment and Context-Specific Label Space", RFC
5331, August 2008.

[RFC5332] Eckert, T., Rosen, E., Aggarwal, R., and Y. Rekhter, "MPLS
Multicast Encapsulations", RFC 5332, August 2008.

[RFC5561] Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL.
Le Roux, "LDP Capabilities", RFC 5561, July 2009.

[RFC6388] Wijnands, IJ., Minei, I., Kompella, K., and B. Thomas,
"Label Distribution Protocol Extensions for Point-to-
Multipoint and Multipoint-to-Multipoint Label Switched
Paths", RFC 6388, November 2011.

[RFC6389] Aggarwal, R. and JL. Le Roux, "MPLS Upstream Label
Assignment for LDP", RFC 6389, November 2011.

[RFC6425] Saxena, S., Swallow, G., Ali, Z., Farrel, A., Yasukawa,
S., and T. Nadeau, "Detecting Data-Plane Failures in
Point-to-Multipoint MPLS - Extensions to LSP Ping", RFC
6425, November 2011.

[RFC6426] Gray, E., Bahadur, N., Boutros, S., and R. Aggarwal, "MPLS
On-Demand Connectivity Verification and Route Tracing",
RFC 6426, November 2011.

10.2. Informative References

[RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
February 2006.

[RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.

Authors' Addresses

Lizhong Jin
Shanghai,
Shanghai
China

Email:

EMail: lizho.jin@gmail.com

Frederic Jounay
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex, FRANCE

Email:
Orange CH
4 rue du Caudray
1007 Lausanne
Switzerland

EMail: frederic.jounay@orange.ch

IJsbrand Wijnands
Cisco Systems, Inc
De kleetlaan 6a
Diegem 1831, 1831
Belgium

Email:

EMail: ice@cisco.com

Nicolai Leymann
Deutsche Telekom AG
Winterfeldtstrasse 21
Berlin 10781

Email:
Germany

EMail: N.Leymann@telekom.de