Segment Routing MPLS Point-to-Multipoint (P2MP) Policy Ping
draft-ietf-pim-p2mp-policy-ping-19

Network Working Group                                    H. Bidgoli, Ed.
Internet-Draft                                                     Nokia
Intended status: Standards Track                                  Z. Ali
Expires: 25 February 2026                                   Cisco System
                                                                Z. Zhang
                                                        Juniper Networks
                                                           A. BudhirajaC
                                                                D. Voyer
                                                            Cisco System
                                                          24 August 2025

      Segment Routing MPLS Point-to-Multipoint (P2MP) Policy Ping
                   draft-ietf-pim-p2mp-policy-ping-19

Abstract

   Point-to-Multipoint (P2MP) Policies are used to define and manage
   explicit P2MP paths within a network.  These policies are typically
   calculated via a controller-based mechanism and installed via, e.g.,
   a Path Computation Element (PCE).  In other cases these policies can
   be installed via using NETCONF/YANG or CLI.  They are used to steer
   multicast traffic along optimized paths from a Root to a set of Leaf
   routers.

   This document defines extensions to Ping and Traceroute mechanisms
   for SR-P2MP Policy with MPLS encapsulation to provide OAM
   (Operations, Administration, and Maintenance) capabilities.  The
   extensions enable operators to verify connectivity, diagnose failures
   and troubleshoot forwarding issues within P2MP Policy multicast
   trees.

   By introducing new mechanisms for detecting failures and validating
   path integrity, this document enhances the operational robustness of
   P2MP multicast deployments.  Additionally, it ensures that existing
   MPLS and SR-based OAM tools can be effectively applied to networks
   utilizing P2MP Policies.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
   3.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  MPLS P2MP Policy Ping and Traceroute  . . . . . . . . . .   4
       3.1.1.  Applicability of current RFC to SR P2MP Policies  . .   4
       3.1.2.  Conformance to Existing Procedures and Additional
               Considerations  . . . . . . . . . . . . . . . . . . .   6
       3.1.3.  Considerations for Interworking with Unicast SR
               Domains . . . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  Packet format and new TLVs  . . . . . . . . . . . . . . .   6
       3.2.1.  Identifying a P2MP Policy . . . . . . . . . . . . . .   7
         3.2.1.1.  SR MPLS P2MP Policy Tree Instance FEC Stack
                 Sub-TLVs  . . . . . . . . . . . . . . . . . . . . .   7
     3.3.  Limiting the Scope of Response  . . . . . . . . . . . . .   8
   4.  Implementation Status . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Nokia Implementation  . . . . . . . . . . . . . . . . . .   9
   5.  IANA Consideration  . . . . . . . . . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

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1.  Introduction

   [draft-ietf-pim-sr-p2mp-policy] explains the concept of the P2MP
   Policy and its Candidate Paths (CPs).  It also explains the concept
   of how a CP is selected to be the active CP.  To enable seamless
   global optimization a CP may consist of multiple P2MP Tree Instances
   (PTIs), allowing for Make-Before-Break (MBB) procedures between an
   active PTI and a newly established, optimized PTI.  A PTI is the
   actual P2MP tunnel set up from the Root to a set of Leaves via
   transit routers.  A PTI is identified on the Root node by the PTI's
   instance ID.

   To ensure reliable network operation, it is essential to verify end-
   to-end connectivity for both active and backup CPs, as well as all
   associated PTIs.  This document specifies a mechanism for detecting
   data plane failures within a P2MP Policy CP and its associated PTIs,
   enabling operators to monitor and troubleshoot multicast path
   integrity.

   This specification applies exclusively to Replication Segments
   (Replication SIDs) that use MPLS encapsulation for forwarding and
   does not cover Segment Routing over IPv6 (SRv6).  The mechanisms
   described herein build upon the concepts established in [RFC6425] for
   P2MP MPLS Operations, Administration, and Maintenance (OAM).  All
   considerations and limitations described in section 6 of [RFC6425]
   apply to this document as well.

1.1.  Terminology

   The readers of this document should familiarize themselves with the
   following documents and sections for terminology and details
   implementation of the P2MP SR Policy

   [RFC9524] section 1.1 defines terms specific to SR Replication
   Segment and also explains the Node terminology in a Multicast domain,
   including the Root Node, Leaf Node and a Bud Node.

   [draft-ietf-pim-sr-p2mp-policy] section 2, defines terms and concepts
   specific to SR P2MP Policy including the CP and the PTI.

2.  Conventions used in this document

   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.

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3.  Motivation

   A P2MP Policy and its corresponding Replication Segments are
   typically provisioned via a centralized controller or configured
   using NETCONF/YANG or CLI.  The root and the leaves are discovered in
   accordance with [draft-ietf-pim-sr-p2mp-policy] and the multicast
   tree is computed from the root to the leaves.  However, there is no
   underlay signaling protocol to distribute the P2MP Policy from the
   root to the leaf routers.  Consequently, when a P2MP tree fails to
   deliver user traffic, identifying the failure can be challenging
   without ping and traceroute mechanisms to isolate faults along the
   tree.

   To address this challenge, P2MP Policy ping and traceroute can be
   utilized to detect and localize faults within the P2MP tree and its
   associated Replication Segments, as defined in [RFC9524].  These OAM
   tools enable periodic ping operations to verify connectivity between
   the root and the leaves.  In cases where a ping fails, a traceroute
   can be initiated to determine the point of failure along the tree.
   This diagnostic process can be initiated from the node responsible
   for establishing the P2MP Policy, ensuring proactive monitoring and
   fault detection.

3.1.  MPLS P2MP Policy Ping and Traceroute

   Ping/Traceroute packets are forwarded based upon the P2MP Policy, on
   a specific CP and its PTI toward the designated leaf routers.  These
   packets are replicated at the replication point based on the
   Replication Segment forwarding information on the corresponding
   router.

   Packets are processed based on the standard behavior when their Time-
   to-Live (TTL) expires or when they reach the egress (leaf) router.
   The appropriate response is sent back to the root node following the
   procedures outlined in [RFC6425].

3.1.1.  Applicability of current RFC to SR P2MP Policies

   The procedures in [RFC6425] define fault detection and isolation
   mechanisms for P2MP MPLS LSPs and extend the LSP ping techniques
   described in [RFC8029] such that they may be applied to P2MP MPLS
   LSPs, ensuring alignment with existing fault management tools.
   [RFC6425] emphasizes the reuse of existing LSP ping mechanisms
   designed for Point-to-Point P2P LSPs, adapting them to P2MP MPLS LSPs
   to facilitate seamless implementation and network operation.

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   The fault detection procedures specified in [RFC6425] are applicable
   to all P2MP MPLS protocols, including P2MP RSVP-TE and Multicast LDP
   and now P2MP SR Policy.  While [RFC6425] highlights specific
   differences for P2MP RSVP-TE and Multicast LDP, this document
   introduces considerations unique to P2MP SR Policies, including:

   1.  Egress Address P2MP Responder Sub-TLVs: Multicast LDP, as per
       section 3.2.1 of [RFC6425], does not allow for the inclusion of
       Egress Address P2MP Responder Sub-TLVs, as upstream LSRs lack
       visibility into downstream leaf nodes.  Similarly, P2MP SR
       Policies often rely on a Path Computation Element (PCE) for
       programming transit routers.  This is why in P2MP SR domain,
       transit routers do not have knowledge of the leaf nodes.  Only
       the Root node, where the P2MP SR Policy is programmed, may have
       visibility into the leaf nodes.  Consequently, these Sub-TLVs
       SHOULD NOT be used when an echo request carries a P2MP Policy
       MPLS Candidate Path FEC.  If a node receives the Egress Address
       P2MP Responder Sub-TLVs in an echo request, then it will not
       respond since it is unaware of whether it lies on the path to the
       address in the sub-TLV.

   2.  End of Processing for Traceroutes: In Multicast LDP LSPs, the
       initiating LSR may not always be aware of all egress nodes,
       unlike P2MP RSVP-TE.  In the case of P2MP SR Policies, the Root
       of the tree may have full visibility into the egress nodes if the
       P2MP SR Policy is PCC-initiated.  If the P2MP SR Policy is PCE-
       initiated, the Root may or may not have visibility into the
       egress nodes, as this depends on the specific implementation and
       configuration of the PCE.  Based on this, a P2MP SR Policy SHOULD
       follow the recommendations in Section 4.3.1 of [RFC6425],
       depending on the level of visibility the Root has into the egress
       nodes.  For example, in a PCC-initiated P2MP SR Policy, the Root
       can learn egress node identities through Next-Generation MVPN
       procedures and BGP, as described in [RFC6514].  In contrast, for
       a PCE-initiated P2MP SR Policy, the PCE may not provide the
       egress node information to the Root, making this process optional
       and implementation-specific.

   3.  Identification of the LSP under test: [RFC6425], in Section 3.1,
       defines distinct identifiers for P2MP RSVP-TE and Multicast LDP
       when identifying an LSP under test.  As each protocol has its own
       identifier, this document introduces a new Target FEC Stack TLV
       specific to P2MP SR Policies to uniquely identify their Candidate
       Paths (CPs) and P2MP Tree Instances (PTIs).  These modifications
       ensure that P2MP Policy OAM mechanisms are properly aligned with
       existing MPLS ping and traceroute tools while addressing the
       specific operational characteristics of P2MP SR Policies.

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3.1.2.  Conformance to Existing Procedures and Additional Considerations

   In addition to major differences outlined in the previous section,
   P2MP SR Policies SHOULD follow to the common procedures specified in
   [RFC6425] for P2MP MPLS LSPs.  Furthermore, this specification reuses
   the same destination UDP port as defined in [RFC8029] for consistency
   with existing MPLS OAM mechanism.

   Implementations MUST account for the fact that a P2MP Policy may
   contain multiple CPs, and each CP may consist of multiple PTIs.  As
   such, implementations SHOULD support the ability to individually test
   each CP and its corresponding PTI using ping and traceroute
   mechanisms.  The ping and traceroute packets are forwarded along the
   specified CP and its PTI, traversing the associated Replication
   Segments.  When a downstream node capable of understanding the
   replication SID receives a ping or traceroute packet, it MUST process
   the request and generate a response even if the CP and its PTI are
   not currently the active path.

3.1.3.  Considerations for Interworking with Unicast SR Domains

   In certain deployments, two Replication Segments may be
   interconnected via an intermediate Unicast SR domain, as an example
   ingress replication.  In such scenarios, proper TTL handling is
   required based on the hierarchical MPLS TTL mode being used (e.g.,
   Pipe Mode vs. Uniform Mode).  For example, when a P2MP Policy Ping or
   Traceroute packet between two Replication Segment is transiting over
   an Unicast SR domain, it must be only processed on Replication
   Segments, based on the Replication SID's TTL value.  The Unicast SR
   domain MUST be treated as a single hop for Replication SID's TTL
   value, meaning that the Replication SID TTL MUST be decremented by
   one before it is forwarded through the Unicast SR domain and the
   replication SID TTL should be examined on the next replication
   segment.  The Unicast SR domain Failure detection is considered out
   of scope for this document.  The operator can use the OAM mechanisms
   available for Unicast SR to farther troubleshoot the Unicast SR
   domain.

3.2.  Packet format and new TLVs

   The packet format used in this specification follow section 3 of
   [RFC8029].  However, additional TLVs and sub-TLVs are required to
   support the new functionality introduced for P2MP Policies.  These
   extensions are described in the following sections.

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3.2.1.  Identifying a P2MP Policy

   [RFC8029] defines a standardized mechanism for detecting data-plane
   failures in Multiprotocol Label Switching (MPLS) Label Switched Paths
   (LSPs).  To correctly identify the Replication Segment associated
   with a given Candidate Path (CP) and P2MP Tree Instance (PTI), the
   Echo Request message MUST include a Target FEC Stack TLV that
   explicitly specifies the Candidate Path and P2MP Tree Instance under
   test.

   This document introduces a new sub-TLV, referred to as the SR MPLS
   P2MP Policy Tree Instance sub-TLV, which is defined as follows:

   Sub-Type       Length            Value Field
   --------       ------            -----------
       41        Variable          SR MPLS P2MP Policy Tree Instance

   Further details regarding the structure and processing of this sub-
   TLV are provided in subsequent sections.

3.2.1.1.  SR MPLS P2MP Policy Tree Instance FEC Stack Sub-TLVs

   The SR MPLS P2MP Policy Tree Instance sub-TLV value field follows the
   format specified in Section 2.3 of [draft-ietf-pim-sr-p2mp-policy].
   The structure of this sub-TLV is illustrated in the figure below.  It
   should be noted that this sub-TLV is testing a specific PTI within a
   specific CP and it is not testing the CP.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        Address Family         | Address Length|   Reserved    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                            Root                               ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Tree-ID                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Instance-ID               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   *  Address Family: (2 octets) IPv4/IPv6 ADDRESS FAMILY NUMBERS as
      specified in [IANA-AF] , indicating the address family of the
      Root.  Any other Address Family but IPv4/IPv6 is not supported by
      this draft.

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   *  Address Length: (1 octet) specifying the length of the Root
      Address in octets (4 octets for IPv4, 16 octets for IPv6).

   *  Reserved: Must be set to zero.

   *  Root: (variable length depending on the address family field) The
      root node of the P2MP Policy, as defined in
      [draft-ietf-pim-sr-p2mp-policy]

   *  Tree-ID: (4 octets) A unique identifier for the P2MP tree, as
      defined in [draft-ietf-pim-sr-p2mp-policy]

   *  Instance-ID: (2 octets) identifies the specific Path-Instance as
      defined in[draft-ietf-pim-sr-p2mp-policy]

3.3.  Limiting the Scope of Response

   As specified in section 3.2 of [RFC6425] , four sub-TLVs are used
   within the P2MP Responder Identifier TLV included in the echo request
   message.

   The Sub-TLVs for IPv4 and IPv6 egress addresses of P2MP responder are
   aligned with section 3.2.1 of [RFC6425].

   The sub-TLVs for IPv4 and IPv6 node addresses of the P2MP responder
   are aligned with Section 3.2.2 of [RFC6425]

   These mechanisms ensure that responses are appropriately scoped to
   limit unnecessary processing and improve the efficiency of P2MP OAM
   procedures.

4.  Implementation Status

   Note to the RFC Editor: please remove this section before
   publication.  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,

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   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".

4.1.  Nokia Implementation

   Nokia has implemented [draft-ietf-pim-sr-p2mp-policy] and [RFC9524].
   In addition, Nokia has implemented P2MP policy ping as defined in
   this draft to verify the end to end connectivity of a P2MP tree in
   segment routing domain.  The implementation supports SR-MPLS
   encapsulation and has all the MUST and SHOULD clause in this draft.
   The implementation is at general availability maturity and is
   compliant with the latest version of the draft.  The documentation
   for implementation can be found at Nokia help and the point of
   contact is hooman.bidgoli@nokia.com.

5.  IANA Consideration

   IANA has assigned a TEMPORARY code point for the "SR MPLS P2MP Policy
   Tree Instance" Sub-TLV Name.  This Sub-TLV is assigned from TLV type
   1 (Target FEC Stack) from the "Multi-Protocol Label Switching (MPLS)
   Label Switched Paths (LSPs) Ping Parameters" registry group.  The
   Sub-TLVs for TLV type 1 are listed under "Sub-TLVs for TLV Types 1,
   16, and 21" sub-registry.  This sub-type value is assigned from the
   standards Action range of 0-16383 from the "Sub-TLVs for TLV Types 1,
   16, and 21" sub-registry.

   Sub-Type Sub-TLV Name

   41 SR MPLS P2MP Policy Tree Instance

6.  Security Considerations

   Overall, the security needs for P2MP policy ping are the same as
   [draft-ietf-pim-sr-p2mp-policy] and[RFC8029].  The P2MP policy ping
   is susceptible to the same three attack vectors as explained in
   RFC8029 section 5.  The same procedures and recommendations explained
   in [RFC8029] section 5 should be taken and implemented to mitigate
   these attack vectors for P2MP policy Ping as well.

7.  Acknowledgments

8.  References

8.1.  Normative References

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   [draft-ietf-pim-sr-p2mp-policy]
              "D. Yoyer, C. Filsfils, R.Prekh, H.bidgoli, Z. Zhang,
              "draft-ietf-pim-sr-p2mp-policy"", July 2025.

   [RFC2119]  "S. Brandner, "Key words for use in RFCs to Indicate
              Requirement Levels"", March 1997.

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

   [RFC6514]  "R.Aggarwal, E. Rosen, T. Morin, Y. Rekhter "BGP Encodings
              and Procedures for Multicast in MPLS/BGP IP VPNs"",
              February 2012.

   [RFC8029]  "K. Kompella, G. Swallow, C. Pgnataro, N. kumar, S. Aldrin
              M.  Chen, "Detecting Multiprotocol Label Switched (MPLS)
              Data-Plane Failures.", February 2006.

   [RFC8174]  "B. Leiba, "ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words"", May 2017.

   [RFC9524]  "D. Voyer, C. Filsfils, R. Parekh, H. Bidgoli, Z. Zhang,
              "Segment Routing Replication for Multipoint Service
              Delivery"", February 2024.

8.2.  Informative References

   [IANA-AF]  "IANA Assigned Port Numbers,
              "http://www.iana.org/assignments/address-family-numbers"".

Authors' Addresses

   Hooman Bidgoli (editor)
   Nokia
   Ottawa
   Canada
   Email: hooman.bidgoli@nokia.com

   Zafar
   Cisco System
   San Jose,
   United States of America
   Email: zali@cisco.com

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   Zhaohui Zhang
   Juniper Networks
   Boston,
   United States of America
   Email: zzhang@juniper.net

   Anuj Budhiraja
   Cisco System
   San Jose,
   United States of America
   Email: abudhira@cisco.com

   Daniel Voyer
   Cisco System
   Montreal
   Canada
   Email: davoyer@cisco.com

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