Multicast-only Fast Reroute Based on Topology Independent Loop-free Alternate (TI-LFA) Fast Reroute
draft-ietf-pim-mofrr-tilfa-14

PIM Working Group                                                 Y. Liu
Internet-Draft                                              China Mobile
Intended status: Informational                                M. McBride
Expires: 9 October 2025                                        Futurewei
                                                                Z. Zhang
                                                                     ZTE
                                                                  J. Xie
                                                                  Huawei
                                                                  C. Lin
                                                    New H3C Technologies
                                                            7 April 2025

  Multicast-only Fast Reroute Based on Topology Independent Loop-free
                    Alternate (TI-LFA) Fast Reroute
                     draft-ietf-pim-mofrr-tilfa-14

Abstract

   This document specifies the use of Topology Independent Loop-Free
   Alternate (TI-LFA) mechanisms with Multicast Only Fast ReRoute
   (MoFRR) for Protocol Independent Multicast (PIM).  The TI-LFA
   provides fast reroute protection for unicast traffic in IP networks
   by precomputing backup paths that avoid potential failures.  By
   integrating TI-LFA with MoFRR, this document extends the benefits of
   fast reroute mechanisms to multicast traffic, enabling enhanced
   resilience and minimized packet loss in multicast networks.  The
   document outlines an optional approach to implement TI-LFA in
   conjunction with MoFRR for PIM, ensuring that multicast traffic is
   rapidly rerouted in the event of a failure.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on 9 October 2025.

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Copyright Notice

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  LFA for MoFRR . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  TI-LFA for MoFRR  . . . . . . . . . . . . . . . . . . . .   5
   3.  A Solution  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  Procedure . . . . . . . . . . . . . . . . . . . . . . . .   7
   4.  Illustration  . . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Management and Operational Considerations . . . . . . . . . .  11
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  15
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   Multicast-only Fast Reroute (MoFRR), as defined in [RFC7431], offers
   a mechanism to reduce multicast packet loss in the event of node or
   link failures by introducing simple enhancements to multicast routing
   protocols, such as Protocol Independent Multicast (PIM) [RFC7761].
   However, the [RFC7431] MoFRR mechanism, which selects the secondary
   multicast next-hop based solely on the loop-free alternate fast
   reroute defined in [RFC7431], has limitations in certain multicast
   deployment scenarios (see Section 2).

   This document introduces a new mechanism for MoFRR using Topology
   Independent Loop-Free Alternate (TI-LFA)
   [I-D.ietf-rtgwg-segment-routing-ti-lfa] fast reroute.  Unlike

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   conventional methods, TI-LFA is independent of network topology,
   enabling broader coverage across diverse network environments.  This
   mechanism is applicable to PIM networks,including cases where PIM
   operates natively over IP in Segment Routing (SR) networks.

   The TI-LFA mechanism is designed for standard link-state Interior
   Gateway Protocol (IGP) shortest path and SR scenarios.  For each
   destination advertised by the IGP in a network, TI-LFA pre-installs a
   backup forwarding entry for the protected destination, ready to be
   activated upon the detection of a link failure used to reach that
   destination.  This document leverages the backup path computed by TI-
   LFA through the IGP as a secondary Upstream Multicast Hop (UMH) for
   PIM.  By sending PIM secondary Join messages hop by hop on the TI-LFA
   backup path, a fast reroute backup path can be created for PIM
   multicast.

   The techniques described in this document are limited to protecting
   links and nodes within a link-state IGP area.  Protecting domain exit
   routers and/or links attached to other routing domains is beyond the
   scope of this document.  All the Segment Identifiers (SIDs) required
   are contained within the Link State Database (LSDB) of the IGP.

   The approach does not alter the existing management and operation of
   LFA, RLFA, and TI-LFA [RFC7916] [RFC8102]
   [I-D.ietf-rtgwg-segment-routing-ti-lfa].  Additionally, during post-
   failure reconvergence, micro-loops [RFC5715] may form due to
   transient forwarding inconsistencies across routers.  PIM micro-loop
   prevention is out of scope for this document.

   Note that this document introduces an optional approach for backup
   Join paths, designed to enhance the protection scope of existing
   multicast systems.  It is fully compatible with current protocol
   implementations and does not necessitate any changes to the protocols
   or forwarding functions on intermediate nodes.  All nodes along the
   backup Join paths must support the RPF Vector attribute as defined in
   [RFC5496] and [RFC7891].  If there is a choice between vector and
   non-vector Join messages on the intermediate nodes, the non-vector
   option should be prioritized, which implies that protection paths
   will remain inactive.  This document does not modify the handling of
   conflicts in PIM Join messages.  For guidance on conflicts in Join
   attributes, please refer to Section 3.3.3 of [RFC5384].

1.1.  Terminology

   This document utilizes the terminology as defined in [RFC7431] and
   incorporates the concepts established in [RFC7490].  The definitions
   of individual terms are not reiterated within this document.

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2.  Problem Statement

2.1.  LFA for MoFRR

   Section 3 of [RFC7431] specifies that a secondary UMH in PIM for
   MoFRR is a Loop-Free Alternate (LFA).  However, the conventional LFA
   mechanism requires that at least one neighbor's next-hop to the
   destination node is a loop-free next-hop.  Due to existing
   limitations of the LFA mechanism in network deployments, such as
   topology dependency and incomplete destination coverage, the LFA
   mechanism can only be deployed in certain network topology
   environments.  In specific network topologies, the secondary UMH
   cannot be computed in PIM for MoFRR, preventing PIM from establishing
   a standby multicast tree and thus from implementing MoFRR protection.
   Consequently, the [RFC7431] MoFRR functionality in PIM is applicable
   only in network topologies where LFA is feasible.

   The limitations of the [RFC7431] MoFRR applicability can be
   illustrated using the example network depicted in Figure 1.  In this
   example, the metric of the R1-R4 link is 20, the metric of the R5-R6
   link is 100, and the metrics of the other links are 10.  All link
   metrics are bidirectional.

   For multicast source S1 and receiver R, the primary path of the PIM
   Join packet is R3->R2->R1, and the secondary path is R3->R4->R1,
   which corresponds to the LFA path of unicast routing.  In this
   scenario, the [RFC7431] MoFRR operates effectively.

   For multicast source S2 and receiver R, the primary path of the PIM
   Join packet is R3->R2.  However, an LFA does not exist.  If R3 sends
   the packet to R4, R4 will forward it back to R3 because the IGP
   shortest path from R4 to R1 is R4->R3->R2.  In this case, the
   [RFC7431] MoFRR cannot calculate a secondary UMH.  Similarly, for
   multicast source S3 and receiver R, the [RFC7431] MoFRR mechanism is
   ineffective.

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                 10           20
            [S1]----(R1)-------------(R4)
                     |                |
                     |                |
                     |10              |10
                 10  |                |
            [S2]----(R2)-------------(R3)----[R]
                     |        10      |   10
                     |                |
                     |10              |10
                 10  |                |
            [S3]----(R5)-----(R6)----(R7)
                         100      10

                     Figure 1: Example Network Topology

2.2.  TI-LFA for MoFRR

   The alternate path provided by the TI-LFA mechanism is represented as
   a Segment List, which includes the NodeSID of the P-space node and
   the Adjacency SIDs of the links between the P-space and Q-space
   nodes.  When a remote PQ node exists in both P-space and Q-space, the
   Segment List requires only the PQ node's NodeSID.

   PIM can look up the corresponding node IP address in the unicast
   route base according to the NodeSID and the IP addresses of the
   endpoints of the corresponding link in the unicast route base
   according to the Adjacency SIDs.  However, multicast protocol packets
   cannot be directly forwarded along the path of the Segment List.

   To establish a standby multicast tree, PIM Join messages need to be
   transmitted hop-by-hop.  However, not all nodes and links on the
   unicast alternate path are included in the Segment List.  If PIM
   protocol packets are transmitted solely in unicast mode, they
   effectively traverse the unicast tunnel like unicast traffic and do
   not pass through the intermediate nodes of the tunnel.  Consequently,
   the intermediate nodes on the alternate path cannot forward multicast
   traffic because they lack PIM state entries.  PIM must create entries
   on each device hop-by-hop, generating an incoming interface and an
   outgoing interface list, to form a complete end-to- end multicast
   tree for forwarding multicast traffic.  Therefore, simply sending PIM
   Join packets using the Segment List, as done with unicast traffic, is
   insufficient to establish a standby multicast tree.

3.  A Solution

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3.1.  Overview

   A secondary UMH serves as a candidate next-hop that can be used to
   reach the root of a multicast tree.  In this document, the secondary
   UMH is derived from unicast routing, utilizing the Segment List
   computed by TI-LFA.

   The path information from the Segment List is incorporated into the
   PIM packets to guide hop-by-hop RPF selection.  The IP address
   corresponding to the Node SID can be used as the segmented root node,
   while the IP addresses of the interfaces at both endpoints of the
   link associated with the Adjacency SID can be used as the local
   upstream interface and upstream neighbor.

   [RFC5496] defines the PIM RPF Vector attribute, which can carry the
   node's IP address corresponding to the Node SID.  Additionally,
   [RFC7891] defines the explicit RPF Vector, which can carry the peer's
   IP address corresponding to the Adjacency SID.

   For instance, in the network illustrated in Figure 1, the secondary
   path for the PIM Join packet towards multicast source S2 cannot be
   computed by [RFC7431] MoFRR, as previously described.  Using TI-LFA,
   R3 sends the packet to R4 while including an RPF Vector that contains
   the IP address of R1, which serves as R3's PQ node for the protected
   R3-R2 link.  R4 then forwards the packet to R1 via the R1- R4 link
   according to the unicast route associated with the RPF Vector.  R1
   subsequently forwards the packet to R2, thus establishing the
   secondary path R3->R4->R1->R2.

   Additionally, for multicast source S3 and receiver R, the primary
   path of the PIM Join packet is R3->R2->R5.  Using TI-LFA, R3 sends
   the PIM Join packet to R7 while including two RPF Vectors:

   *  The first RPF Vector contains the IP address of R6, which serves
      as R3's P-node for the protected R3-R2 link.

   *  The second RPF Vector contains the interface IP addresses of R6
      and R5, which serve as R3's Q-node for the protected R3-R2 link.

   The first RPF Vector guides the PIM Join path through R3->R7->R6,
   while the second RPF Vector guides the PIM Join path through R6->R5,
   thereby establishing the secondary path R3->R7->R6->R5.

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   This document leverages the above RPF Vector standards, obviating the
   need for PIM protocol extensions.  This approach allows the
   establishment of a standby multicast tree based on the Segment List
   calculated by TI-LFA, thereby providing comprehensive MoFRR
   protection for multicast services across diverse network
   environments.

3.2.  Procedure

   Consider a Segment List calculated by TI-LFA as (NodeSID(A),
   AdjSID(A-B)).  Node A belongs to the P-space, and node B belongs to
   the Q-space.  The IP address corresponding to NodeSID(A) can be
   retrieved from the local link-state database of the IGP and assumed
   to be IP-a.  Similarly, the IP addresses of the two endpoints of the
   link corresponding to AdjSID(A-B) can also be retrieved from the
   local link-state database and assumed to be IP-La and IP-Lb.

   Within the PIM process, IP-a is treated as the standard RPF Vector
   Attribute and added to the PIM Join packet.  IP-La is considered the
   local address of the incoming interface, and IP-Lb is regarded as the
   address of the upstream neighbor.  Consequently, IP-Lb can be
   included in the PIM Join packet as the explicit RPF Vector Attribute.

   The PIM protocol initially selects the RPF incoming interface and
   upstream neighbor towards IP-a and proceeds hop-by-hop to establish
   the PIM standby multicast tree until reaching node A.  At node A, IP-
   Lb is treated as the PIM upstream neighbor.  Node A identifies the
   incoming interface in the unicast routing table based on IP-Lb, and
   IP-Lb is used as the RPF upstream address for the PIM Join packet
   directed towards node B.

   Upon receiving the PIM Join packet at node B, the PIM protocol,
   finding no additional RPF Vector Attributes, selects the RPF incoming
   interface and upstream neighbor towards the multicast source
   directly.  The protocol, then, continues hop-by-hop to establish the
   PIM standby multicast tree, extending to the router directly
   connected to the source.

   When a remote PQ node exists in both P-space and Q-space, the
   processing can be simplified to involve only Node A.

4.  Illustration

   This section provides an illustration of MoFRR based on TI-LFA.  The
   example topology is depicted in Figure 2.  The metric for the R3-R4
   link is 100, while the metrics for the other links are 10.  All link
   metrics are bidirectional.

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                     <-----Primary Path--- (S,G) Join

             [S]---(R1)---(R2)******(R6)-------[R]
                            |        |
                     <---   |        |   |
                        |   |        |   |
                        |   |       (R5) |
                        |   |        |   |
                        |   |        |   |
                        |   |        |   |
                        | (R3)------(R4) |
                        |                |
                        --Secondary Path--

                         Figure 2: Example Topology

   The IP addresses and SIDs involved in the MoFRR calculation are
   configured as follows:

   IPv4 Data Plane (MPLS-SR [RFC8660])

     Node    IP Address   Node SID
     R4      IP4-R4       Label-R4

     Link    IP Address   Adjacency SID
     R3->R4  IP4-R3-R4    Label-R3-R4
     R4->R3  IP4-R4-R3    Label-R4-R3

   IPv6 Data Plane (SRv6 [RFC8986])

     Node    IP Address   Node SID (End)
     R4      IP6-R4       SID-R4

     Link    IP Address   Adjacency SID (End.X)
     R3->R4  IP6-R3-R4    SID-R3-R4
     R4->R3  IP6-R4-R3    SID-R4-R3

   The primary path of the PIM Join packet is R6->R2->R1, and the
   secondary path is R6->R5->R4->R3->R2->R1.  However, the traditional
   LFA does not function properly for the secondary path because the
   shortest path to R2 from R5 (or from R4) still traverses the R6-R2
   link.  In this scenario, R6 must calculate the secondary UMH using
   the proposed MoFRR method based on TI-LFA.

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   According to the TI-LFA algorithm, the P-space and Q-space are
   illustrated in Figure 3.  The TI-LFA repair path consists of the Node
   SID of R4 and the Adjacency SID of R4->R3.  On the MPLS-SR data
   plane, the repair segment list is (Label-R4, Label-R4-R3).  On the
   SRv6 data plane, the repair segment list is (SID-R4, SID-R4-R3).

                           ........
                           .      .
                 [S]---(R1)---(R2)******(R6)---[R]
                           .   |  .     |
                           .   |  .  +++|++++
                           .   |  .  +  |   +
                           .   |  .  + (R5) +
                           .   |  .  +  |   +
                           .   |  .  +  |   +
                           .   |  .  +  |   +
                           . (R3)------(R4) +
                           .      .  +      +
                           ........  ++++++++
                           Q-Space    P-Space

                       Figure 3: P-Space and Q-Space

   In the PIM process, the IP addresses associated with the repair
   segment list are retrieved from the IGP link-state database.

   On the IPv4 data plane, the Node SID Label-R4 corresponds to IP4-R4,
   which will be carried in the RPF Vector Attribute.  The Adjacency SID
   Label-R4-R3 corresponds to the local address IP4-R4-R3 and the remote
   peer address IP4-R3-R4, with IP4-R3-R4 carried in the Explicit RPF
   Vector Attribute.

   On the IPv6 data plane, the End SID SID-R4 corresponds to IP6-R4,
   which will be carried in the RPF Vector Attribute.  The End.X SID
   SID-R4-R3 corresponds to the local address IP6-R4-R3 and the remote
   peer address IP6-R3-R4, with IP6-R3-R4 carried in the Explicit RPF
   Vector Attribute.

   Subsequently, R6 installs the secondary UMH using these RPF
   Vectors.

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             +---------+
             |Type = 0 |
             |IP4-R4   |
             +---------+    +---------+
             |Type = 4 |    |Type = 4 |
             |IP4-R3-R4|    |IP4-R3-R4|
             +---------+    +---------+   No RPF Vector

          R6----->R5---->R4------------>R3----->R2---->R1

      Figure 4: Forwarding PIM Join Packet along Secondary Path (IPv4)

   On the IPv4 data plane, the forwarding of the PIM Join packet along
   the secondary path is shown in Figure 4.

   R6 inserts two RPF Vector Attributes in the PIM Join packet: IP4-R4
   of Type 0 (RPF Vector Attribute) and IP4-R3-R4 of Type 4 (Explicit
   RPF Vector Attribute).  R6 then forwards the packet along the
   secondary path.

   When R5 receives the packet, it performs a unicast route lookup of
   the first RPF Vector IP4-R4 and sends the packet to R4.

   R4, being the owner of IP4-R4, removes the first RPF Vector from the
   packet and forwards it according to the next RPF Vector.  R4 sends
   the packet to R3 based on the next RPF Vector IP4-R3-R4, as its PIM
   neighbor R3 corresponds to IP4-R3-R4.

   When R3 receives the packet, as the owner of IP4-R3-R4, it removes
   the RPF Vector.  The packet, now devoid of RPF Vectors, is forwarded
   to the source through R3->R2->R1 based on unicast routes.

   After the PIM Join packet reaches R1, a secondary multicast tree,
   R1->R2->R3->R4->R5->R6, is established hop-by-hop for (S, G) using
   MoFRR based on TI-LFA.

             +---------+
             |Type = 0 |
             |IP6-R4   |
             +---------+    +---------+
             |Type = 4 |    |Type = 4 |
             |IP6-R3-R4|    |IP6-R3-R4|
             +---------+    +---------+   No RPF Vector

          R6----->R5---->R4------------>R3----->R2---->R1

      Figure 5: Forwarding PIM Join Packet along Secondary Path (IPv6)

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   On the IPv6 data plane, the forwarding of the PIM Join packet along
   the secondary path is illustrated in Figure 5.  The procedure is
   analogous to that of the IPv4 data plane.

   When a remote PQ node exists in both P-space and Q-space, the
   processing can be simplified to involve only the PQ node.  In this
   case, only a single RPF Vector needs to be carried, and all other
   processing steps remain unchanged.

5.  Management and Operational Considerations

   The management of the proposed approach is consistent with [RFC7916].
   But, in the operation of this approach, the node on the backup Join
   paths must have independent configuration strategy for installing RPF
   Vector Attributes in the PIM Join packet and controlling the sending
   of this PIM Join messages.

   All nodes on the backup Join paths must be able to parse the PIM Join
   message with RPF Vector attribute.  If the nodes do not understand
   the RPF Vector attribute in the PIM Join packet, then it must discard
   the RPF Vector attribute because failing to remove the RPF Vectors
   could cause upstream nodes to send the Join back toward these nodes
   causing loops.

   If an administrator is manually specifying the path that the Join
   messages need to be sent on, it is recommended that the administrator
   computes the path to include nodes that support the Explicit RPF
   Vector and check that the state is created correctly on each node
   along the path.  Tools like mtrace [RFC8487] can be used for
   debugging and to ensure that the Join state is setup correctly.

6.  IANA Considerations

   This document has no IANA actions.

7.  Security Considerations

   This document does not introduce additional security concerns.  It
   does not change the security properties of PIM.  For general PIM-SM
   protocol security considerations, see [RFC7761].  The security
   considerations of LFA, R-LFA, and MoFRR described in [RFC5286],
   [RFC7490], and [RFC7431] should apply to this document.

   When deploying TI-LFA, packets may be sent over nodes and links they
   were not transported through before, potentially raising the
   following security issues:

   1.  Spoofing and False Route Advertisements

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       *  Dependencies of LFA/R-LFA/TI-LFA on Routing Information

          -  LFAs depend on accurate routing information to determine
             alternate paths.  If an attacker can inject false routing
             information (e.g., by spoofing link-state advertisements),
             it could cause the network to select suboptimal or
             malicious paths for LFAs.

          -  R-LFA and TI-LFA also depend on accurate routing
             information, particularly for determining the tunneling
             paths or explicit paths.  False route advertisements could
             mislead the network into using insecure or compromised
             paths.

   2.  On-path Attacks

       *  Use of Alternate Paths

          -  By rerouting traffic through alternate paths, especially
             those that traverse multiple hops (as in R-LFA and TI-LFA),
             the risk of On-path attacks increases if any of the
             intermediate routers on the alternate path is compromised.

          -  TI-LFA, which uses explicit paths, might expose traffic to
             routers that were not originally part of the primary path,
             potentially allowing for interception or alteration of the
             traffic.

   3.  Confidentiality and Integrity

       *  Traffic Encapsulation

          -  R-LFA and TI-LFA involve encapsulating traffic, which may
             expose it to vulnerabilities if the encapsulation
             mechanisms are not secure.  For instance, if IPsec or
             another secure encapsulation method is not used, an
             attacker might be able to intercept or alter the traffic in
             transit.

       *  Protection of Explicit Paths

          -  TI-LFA relies on explicit paths that are typically defined
             using segment routing.  If these paths are not properly
             protected, an attacker could manipulate the segment list to
             reroute traffic through malicious nodes.

   4.  Increased Attack Surface

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       *  Extended Topology

          -  By introducing LFA, R-LFA, and TI-LFA, the network
             increases its reliance on additional routers and links,
             thereby expanding the potential attack surface.  Compromise
             of any router in these alternate paths could expose traffic
             to unauthorized access or disruption.

   To address security issues #1 and #2 mentioned above, control plane
   protocols need to provide security protection.  To mitigate the risks
   associated with false route advertisements and On-path attacks, it is
   recommended to use secure routing protocols (e.g., OSPFv3 with IPsec,
   ISIS HMAC-SHA256, or PIM with IPsec) that provide authentication and
   integrity protection for routing updates.

   To address security issues #3 and #4 mentioned above, these
   mechanisms need to run within a trusted network.  The security of
   LFA, R-LFA, and TI-LFA mechanisms heavily relies on the
   trustworthiness of the underlying routing infrastructure.  As the
   solution described in the document is based on Segment Routing
   technology, readers should be aware of the security considerations
   related to this technology ([RFC8402]) and its data plane
   instantiations ([RFC8660], [RFC8754], and [RFC8986]).

8.  References

8.1.  Normative References

   [I-D.ietf-rtgwg-segment-routing-ti-lfa]
              Bashandy, A., Litkowski, S., Filsfils, C., Francois, P.,
              Decraene, B., and D. Voyer, "Topology Independent Fast
              Reroute using Segment Routing", Work in Progress,
              Internet-Draft, draft-ietf-rtgwg-segment-routing-ti-lfa-
              21, 12 February 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-rtgwg-
              segment-routing-ti-lfa-21>.

   [RFC5286]  Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
              IP Fast Reroute: Loop-Free Alternates", RFC 5286,
              DOI 10.17487/RFC5286, September 2008,
              <https://www.rfc-editor.org/info/rfc5286>.

   [RFC5384]  Boers, A., Wijnands, I., and E. Rosen, "The Protocol
              Independent Multicast (PIM) Join Attribute Format",
              RFC 5384, DOI 10.17487/RFC5384, November 2008,
              <https://www.rfc-editor.org/info/rfc5384>.

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   [RFC5496]  Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse Path
              Forwarding (RPF) Vector TLV", RFC 5496,
              DOI 10.17487/RFC5496, March 2009,
              <https://www.rfc-editor.org/info/rfc5496>.

   [RFC7431]  Karan, A., Filsfils, C., Wijnands, IJ., Ed., and B.
              Decraene, "Multicast-Only Fast Reroute", RFC 7431,
              DOI 10.17487/RFC7431, August 2015,
              <https://www.rfc-editor.org/info/rfc7431>.

   [RFC7490]  Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
              So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)",
              RFC 7490, DOI 10.17487/RFC7490, April 2015,
              <https://www.rfc-editor.org/info/rfc7490>.

   [RFC7761]  Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
              Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
              Multicast - Sparse Mode (PIM-SM): Protocol Specification
              (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
              2016, <https://www.rfc-editor.org/info/rfc7761>.

   [RFC7891]  Asghar, J., Wijnands, IJ., Ed., Krishnaswamy, S., Karan,
              A., and V. Arya, "Explicit Reverse Path Forwarding (RPF)
              Vector", RFC 7891, DOI 10.17487/RFC7891, June 2016,
              <https://www.rfc-editor.org/info/rfc7891>.

   [RFC7916]  Litkowski, S., Ed., Decraene, B., Filsfils, C., Raza, K.,
              Horneffer, M., and P. Sarkar, "Operational Management of
              Loop-Free Alternates", RFC 7916, DOI 10.17487/RFC7916,
              July 2016, <https://www.rfc-editor.org/info/rfc7916>.

   [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/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/info/rfc8660>.

   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
              <https://www.rfc-editor.org/info/rfc8754>.

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   [RFC8986]  Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
              D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
              (SRv6) Network Programming", RFC 8986,
              DOI 10.17487/RFC8986, February 2021,
              <https://www.rfc-editor.org/info/rfc8986>.

8.2.  Informative References

   [RFC5715]  Shand, M. and S. Bryant, "A Framework for Loop-Free
              Convergence", RFC 5715, DOI 10.17487/RFC5715, January
              2010, <https://www.rfc-editor.org/info/rfc5715>.

   [RFC8102]  Sarkar, P., Ed., Hegde, S., Bowers, C., Gredler, H., and
              S. Litkowski, "Remote-LFA Node Protection and
              Manageability", RFC 8102, DOI 10.17487/RFC8102, March
              2017, <https://www.rfc-editor.org/info/rfc8102>.

   [RFC8487]  Asaeda, H., Meyer, K., and W. Lee, Ed., "Mtrace Version 2:
              Traceroute Facility for IP Multicast", RFC 8487,
              DOI 10.17487/RFC8487, October 2018,
              <https://www.rfc-editor.org/info/rfc8487>.

Contributors

   Mengxiao Chen
   New H3C Technologies
   China
   Email: chen.mengxiao@h3c.com

Authors' Addresses

   Yisong Liu
   China Mobile
   China
   Email: liuyisong@chinamobile.com

   Mike McBride
   Futurewei Inc.
   USA
   Email: michael.mcbride@futurewei.com

   Zheng(Sandy) Zhang
   ZTE Corporation
   China
   Email: zzhang_ietf@hotmail.com

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   Jingrong Xie
   Huawei Technologies
   China
   Email: xiejingrong@huawei.com

   Changwang Lin
   New H3C Technologies
   China
   Email: linchangwang.04414@h3c.com

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