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Label Switched Path (LSP) Ping for Segment Routing (SR) Path Segment Identifiers (SIDs) with MPLS Data Planes
draft-xp-mpls-spring-lsp-ping-path-sid-09

Document Type Active Internet-Draft (candidate for mpls WG)
Authors Xiao Min , Shaofu Peng , Liyan Gong , Rakesh Gandhi , Carlos Pignataro
Last updated 2024-02-26 (Latest revision 2024-01-26)
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draft-xp-mpls-spring-lsp-ping-path-sid-09
MPLS Working Group                                                X. Min
Internet-Draft                                                   S. Peng
Intended status: Standards Track                               ZTE Corp.
Expires: 29 July 2024                                            L. Gong
                                                            China Mobile
                                                               R. Gandhi
                                                     Cisco Systems, Inc.
                                                            C. Pignataro
                                         North Carolina State University
                                                         26 January 2024

  Label Switched Path (LSP) Ping for Segment Routing (SR) Path Segment
                Identifiers (SIDs) with MPLS Data Planes
               draft-xp-mpls-spring-lsp-ping-path-sid-09

Abstract

   Path Segment is a type of Segment Routing (SR) segment, which is used
   to identify an SR path.  This document provides Target Forwarding
   Equivalence Class (FEC) Stack TLV definitions for Path Segment
   Identifiers.

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/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents 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 29 July 2024.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.

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   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   2
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     2.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Path Segment ID Sub-TLVs  . . . . . . . . . . . . . . . . . .   3
     3.1.  SR Policy's Path SID  . . . . . . . . . . . . . . . . . .   3
     3.2.  SR Candidate Path's Path SID  . . . . . . . . . . . . . .   5
     3.3.  SR Segment List's Path SID  . . . . . . . . . . . . . . .   6
   4.  Path-SID FEC Validation . . . . . . . . . . . . . . . . . . .   9
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   Path Segment is a type of SR segment, which is used to identify an SR
   path.  Path Segment in MPLS based segment routing network is defined
   in [I-D.ietf-spring-mpls-path-segment].

   As specified in [I-D.ietf-spring-mpls-path-segment], when a Path
   Segment is used, it's inserted by the ingress node of the SR path,
   and then processed by the egress node of the SR path.  The Path
   Segment Label is placed within the MPLS label stack as the last
   segment identifier of the segment list.  The Path Segment would not
   be popped up until it reaches the egress node, and the egress node
   would pop the path segment up.

   This document provides Target Forwarding Equivalence Class (FEC)
   Stack TLV definitions for Path-SIDs.  Procedures for LSP Ping as
   defined in [RFC8287] and [RFC8690] are applicable to Path-SIDs as
   well.

2.  Conventions

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2.1.  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.

2.2.  Terminology

   This document uses the terminology defined in [RFC3031], [RFC8402],
   and [RFC8029], readers are expected to be familiar with those terms.

3.  Path Segment ID Sub-TLVs

   Analogous to what's defined in Section 5 of [RFC8287] and Section 4
   of [I-D.ietf-mpls-sr-epe-oam], three new sub-TLVs are defined for the
   Target FEC Stack TLV (Type 1), the Reverse-Path Target FEC Stack TLV
   (Type 16), and the Reply Path TLV (Type 21).

        Sub-Type    Sub-TLV Name
        --------    -----------------------------
         TBD1       SR Policy's Path SID
         TBD2       SR Candidate Path's Path SID
         TBD3       SR Segment List's Path SID

   As specified in Section 2 of [I-D.ietf-spring-mpls-path-segment], a
   Path Segment can be used to identify a Segment List, some or all
   Segment lists in a Candidate path or an SR policy, so three different
   Target FEC Stack sub-TLVs need to be defined for Path Segment ID.
   When a Path Segment is used to identify an SR Policy, the Target FEC
   Stack sub-TLV of the type "SR Policy's Path SID" would be used to
   validate the control plane to forwarding plane synchronization for
   this Path-SID; When a Path Segment is used to identify an SR
   Candidate Path, the Target FEC Stack sub-TLV of the type "SR
   Candidate Path's Path SID" would be used to validate the control
   plane to forwarding plane synchronization for this Path-SID; When a
   Path Segment is used to identify a Segment List, the Target FEC Stack
   sub-TLV of the type "SR Segment List's Path SID" would be used to
   validate the control plane to forwarding plane synchronization for
   this Path-SID.  Note that the three new Target FEC Stack sub-TLVs are
   mutual exclusive and they wouldn't be present in one message
   simultaneously.

3.1.  SR Policy's Path SID

   The format of SR Policy's Path SID sub-TLV is specified as below:

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    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Type = TBD1          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                     Headend  (4/16 octets)                    ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Color  (4 octets)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                    Endpoint  (4/16 octets)                    ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 1: SR Policy's Path SID sub-TLV

   Type

      This field is set to the value (TBD1) which indicates that it's an
      SR Policy's Path SID sub-TLV.

   Length

      This field is set to the length of the sub-TLV's Value field in
      octets.  If Headend and Endpoint fields are in IPv4 address format
      which is 4 octets long, it MUST be set to 12; If Headend and
      Endpoint fields are in IPv6 address format which is 16 octets
      long, it MUST be set to 36.

   Headend

      This field identifies the headend of an SR Policy, the same as
      defined in Section 2.1 of [RFC9256].  The headend is a 4-octet
      IPv4 address or a 16-octet IPv6 address.

   Color

      This field associates the SR Policy with an intent or objective
      (e.g., low latency), the same as defined in Section 2.1 of
      [RFC9256].  The color is an unsigned non-zero 4-octet integer
      value.

   Endpoint

      This field identifies the endpoint of an SR Policy, the same as
      defined in Section 2.1 of [RFC9256].  The endpoint is a 4-octet
      IPv4 address or a 16-octet IPv6 address.

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3.2.  SR Candidate Path's Path SID

   The format of SR Candidate Path's Path SID sub-TLV is specified as
   below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Type = TBD2          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                     Headend  (4/16 octets)                    ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Color  (4 octets)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                    Endpoint  (4/16 octets)                    ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Protocol-Origin|                    Reserved                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                                                               |
   |                  Originator  (20 octets)                      |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Discriminator  (4 octets)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 2: SR Candidate Path's Path SID sub-TLV

   Type

      This field is set to the value (TBD2) which indicates that it's an
      SR Candidate Path's Path SID sub-TLV.

   Length

      This field is set to the length of the sub-TLV's Value field in
      octets.  If Headend and Endpoint fields are in IPv4 address format
      which is 4 octets long, it MUST be set to 40; If Headend and
      Endpoint fields are in IPv6 address format which is 16 octets
      long, it MUST be set to 64.

   Headend

      This field identifies the headend of an SR Policy, the same as
      defined in Section 2.1 of [RFC9256].  The headend is a 4-octet
      IPv4 address or a 16-octet IPv6 address.

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   Color

      This field associates the SR Policy with an intent or objective
      (e.g., low latency), the same as defined in Section 2.1 of
      [RFC9256].  The color is an unsigned non-zero 4-octet integer
      value.

   Endpoint

      This field identifies the endpoint of an SR Policy, the same as
      defined in Section 2.1 of [RFC9256].  The endpoint is a 4-octet
      IPv4 address or a 16-octet IPv6 address.

   Protocol-Origin

      This field is associated with the mechanism or protocol used for
      signaling/provisioning the SR Policy, the same as defined in
      Section 2.3 of [RFC9256].  The protocol-origin of a candidate path
      is a 1-octet value indicating PCEP, BGP SR Policy, or Via
      Configuration.  The value of protocol-origin is set as specified
      in Section 2.3 of [RFC9256].

   Originator

      This field identifies the node that provisioned or signaled the
      candidate path on the headend, the same as defined in Section 2.4
      of [RFC9256].  The originator is a 20-octet numerical value formed
      by the concatenation of the fields of the tuple <Autonomous System
      Number (ASN), node-address>, among which ASN is a 4-octet number
      and node address is a 16-octet value (an IPv6 address or an IPv4
      address encoded in the lowest 4 octets).  When procotol-origin is
      respectively indicating Via Configuration, PCEP, or BGP SR Policy,
      the value of originator is set as specified in Section 2.4 of
      [RFC9256].

   Discriminator

      This field uniquely identifies a candidate path within the context
      of an SR policy from a specific protocol-origin, the same as
      defined in Section 2.5 of [RFC9256].  The discriminator is a
      4-octet value.  When protocol-origin is respectively indicating
      Via Configuration, PCEP, or BGP SR Policy, the value of
      discriminator is set as specified in Section 2.5 of [RFC9256].

3.3.  SR Segment List's Path SID

   The format of SR Segment List's Path SID sub-TLV is specified as
   below:

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    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Type = TBD3          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                     Headend  (4/16 octets)                    ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Color  (4 octets)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                    Endpoint  (4/16 octets)                    ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Protocol-Origin|                    Reserved                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                                                               |
   |                  Originator  (20 octets)                      |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Discriminator  (4 octets)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Segment-List-ID  (4 octets)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 3: SR Segment List's Path SID sub-TLV

   Type

      This field is set to the value (TBD3) which indicates that it's an
      SR Segment List's Path SID sub-TLV.

   Length

      This field is set to the length of the sub-TLV's Value field in
      octets.  If Headend and Endpoint fields are in IPv4 address format
      which is 4 octets long, it MUST be set to 44; If Headend and
      Endpoint fields are in IPv6 address format which is 16 octets
      long, it MUST be set to 68.

   Headend

      This field identifies the headend of an SR Policy, the same as
      defined in Section 2.1 of [RFC9256].  The headend is a 4-octet
      IPv4 address or a 16-octet IPv6 address.

   Color

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      This field associates the SR Policy with an intent or objective
      (e.g., low latency), the same as defined in Section 2.1 of
      [RFC9256].  The color is an unsigned non-zero 4-octet integer
      value.

   Endpoint

      This field identifies the endpoint of an SR Policy, the same as
      defined in Section 2.1 of [RFC9256].  The endpoint is a 4-octet
      IPv4 address or a 16-octet IPv6 address.

   Protocol-Origin

      This field is associated with the mechanism or protocol used for
      signaling/provisioning the SR Policy, the same as defined in
      Section 2.3 of [RFC9256].  The protocol-origin of a candidate path
      is a 1-octet value indicating PCEP, BGP SR Policy, or Via
      Configuration.  The value of protocol-origin is set as specified
      in Section 2.3 of [RFC9256].

   Originator

      This field identifies the node that provisioned or signaled the
      candidate path on the headend, the same as defined in Section 2.4
      of [RFC9256].  The originator is a 20-octet numerical value formed
      by the concatenation of the fields of the tuple <Autonomous System
      Number (ASN), node-address>, among which ASN is a 4-octet number
      and node address is a 16-octet value (an IPv6 address or an IPv4
      address encoded in the lowest 4 octets).  When procotol-origin is
      respectively indicating Via Configuration, PCEP, or BGP SR Policy,
      the value of originator is set as specified in Section 2.4 of
      [RFC9256].

   Discriminator

      This field uniquely identifies a candidate path within the context
      of an SR policy from a specific protocol-origin, the same as
      defined in Section 2.5 of [RFC9256].  The discriminator is a
      4-octet value.  When protocol-origin is respectively indicating
      Via Configuration, PCEP, or BGP SR Policy, the value of
      discriminator is set as specified in Section 2.5 of [RFC9256].

   Segment-List-ID

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      This field identifies an SR path within the context of a candidate
      path of an SR Policy, the same as "Path ID" defined in Section 4.2
      of [I-D.ietf-pce-multipath], or "Segment List ID" defined in
      Section 2.1 of [I-D.ietf-idr-sr-policy-seglist-id].  The segment-
      list-id is a 4-octet identifier of a segment list.

4.  Path-SID FEC Validation

   The MPLS LSP Ping procedures may be initiated by the headend of the
   Segment Routing path or a centralized topology-aware data plane
   monitoring system as described in [RFC8403].  For the Path-SID, the
   responder nodes that receive echo request and send echo reply MUST be
   the endpoint of the Segment Routing path.

   When an endpoint receives the LSP echo request packet with top FEC
   being the Path-SID, it SHOULD perform validity checks on the content
   of the Path-SID FEC Stack sub-TLV.  The basic length check should be
   performed on the received FEC.

       SR Policy's Path SID
       ------------------
       Length = 12 or 36 octets

       SR Candidate Path's Path SID
       ------------------
       Length = 40 or 64 octets

       SR Segment List's Path SID
       ------------------
       Length = 44 or 68 octets

   If a malformed FEC Stack sub-TLV is received, then a return code of
   1, "Malformed echo request received" as defined in [RFC8029] SHOULD
   be sent.  The below section augments Section 7.4 of [RFC8287].

      4a.  Segment Routing Path-SID Validation:

      If the Label-stack-depth is 0 and the Target FEC Stack sub-TLV at
      FEC-stack-depth is TBD1 (SR Policy's Path SID sub-TLV), {

      -  Set the Best-return-code to 10, "Mapping for this FEC is not
         the given label at stack-depth <RSC>" if any below conditions
         fail (the notation <RSC> refers to the Return Subcode):

         o  Validate that the Path Segment ID is signaled or provisioned
            for the SR Policy {

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            +  Validate that the signaled or provisioned headend, color
               and end-point for the Path SID, matches with the
               corresponding fields in the received SR Policy's Path SID
               sub-TLV.

            }

         }

      -  If all the above validations have passed, set the return code
         to 3 "Replying router is an egress for the FEC at stack-depth
         <RSC>".

      -  Set FEC-Status to 1 and return.

      }

      Else, if the Label-stack-depth is 0 and the Target FEC Stack sub-
      TLV at FEC-stack-depth is TBD2 (SR Candidate Path's Path SID sub-
      TLV), {

      -  Set the Best-return-code to 10, "Mapping for this FEC is not
         the given label at stack-depth <RSC>" if any below conditions
         fail:

         o  Validate that the Path Segment ID is signaled or provisioned
            for the SR Candidate Path {

            +  When the Protocol-Origin field in the received SR
               Candidate Path's Path SID sub-TLV is a value indicating
               PCEP, "PCEP" is the used signaling protocol.  And then
               validate that the Path Segment ID matches with the tuple
               identifying the SR Candidate Path within PCEP {

               *  Validate that the signaled headend, color, end-point,
                  originator ASN, originator address and discriminator
                  defined in [I-D.ietf-pce-segment-routing-policy-cp]
                  and [I-D.ietf-pce-sr-path-segment], for the Path SID,
                  matches with the corresponding fields in the received
                  SR Candidate Path's Path SID sub-TLV.

               }

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            +  When the Protocol-Origin field in the received SR
               Candidate Path's Path SID sub-TLV is a value indicating
               BGP SR Policy, "BGP SR Policy" is the used signaling
               protocol.  And then validate that the Path Segment ID
               matches with the tuple identifying the SR Candidate Path
               within BGP SR Policy {

               *  Validate that the signaled headend, policy color,
                  endpoint, ASN, BGP Router-ID and distinguisher defined
                  in [I-D.ietf-idr-segment-routing-te-policy] and
                  [I-D.ietf-idr-sr-policy-path-segment], for the Path
                  SID, matches with the corresponding fields in the
                  received SR Candidate Path's Path SID sub-TLV.

               }

            +  When the Protocol-Origin field in the received SR
               Candidate Path's Path SID sub-TLV is a value indicating
               Via Configuration, "Via Configuration" is the used
               provisioning mechanism.  And then validate that the Path
               Segment ID matches with the tuple identifying the SR
               Candidate Path within Configuration {

               *  Validate that the provisioned headend, color,
                  endpoint, originator and discriminator, for the Path
                  SID, matches with the corresponding fields in the
                  received SR Candidate Path's Path SID sub-TLV.

               }

            }

      -  If all the above validations have passed, set the return code
         to 3 "Replying router is an egress for the FEC at stack-depth
         <RSC>".

      -  Set FEC-Status to 1 and return.

      }

      Else, if the Label-stack-depth is 0 and the Target FEC Stack sub-
      TLV at FEC-stack-depth is TBD3 (SR Segment List's Path SID sub-
      TLV), {

      -  Set the Best-return-code to 10, "Mapping for this FEC is not
         the given label at stack-depth <RSC>" if any below conditions
         fail:

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         o  Validate that the Path Segment ID is signaled or provisioned
            for the SR Segment List {

            +  When the Protocol-Origin field in the received SR Segment
               List's Path SID sub-TLV is a value indicating PCEP,
               "PCEP" is the used signaling protocol.  And then validate
               that the Path Segment ID matches with the tuple
               identifying the SR Segment List within PCEP {

               *  Validate that the signaled headend, color, end-point,
                  originator ASN, originator address and discriminator
                  defined in [I-D.ietf-pce-segment-routing-policy-cp]
                  and [I-D.ietf-pce-sr-path-segment], and the signaled
                  Path ID defined in [I-D.ietf-pce-multipath], for the
                  Path SID, matches with the corresponding fields in the
                  received SR Segment List's Path SID sub-TLV.

               }

            +  When the Protocol-Origin field in the received SR Segment
               List's Path SID sub-TLV is a value indicating BGP SR
               Policy, "BGP SR Policy" is the used signaling protocol.
               And then validate that the Path Segment ID matches with
               the tuple identifying the SR Segment List within BGP SR
               Policy {

               *  Validate that the signaled headend, policy color,
                  endpoint, ASN, BGP Router-ID and distinguisher defined
                  in [I-D.ietf-idr-segment-routing-te-policy] and
                  [I-D.ietf-idr-sr-policy-path-segment], and the
                  signaled Segment List ID defined in
                  [I-D.ietf-idr-sr-policy-seglist-id], for the Path SID,
                  matches with the corresponding fields in the received
                  SR Segment List's Path SID sub-TLV.

               }

            +  When the Protocol-Origin field in the received SR Segment
               List's Path SID sub-TLV is a value indicating Via
               Configuration, "Via Configuration" is the used
               provisioning mechanism.  And then validate that the Path
               Segment ID matches with the tuple identifying the SR
               Segment List within Configuration {

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               *  Validate that the provisioned headend, color,
                  endpoint, originator, discriminator and Segment-List-
                  ID, for the Path SID, matches with the corresponding
                  fields in the received SR Segment List's Path SID sub-
                  TLV.

               }

            }

      -  If all the above validations have passed, set the return code
         to 3 "Replying router is an egress for the FEC at stack-depth
         <RSC>".

      -  Set FEC-Status to 1 and return.

      }

5.  Security Considerations

   This document defines additional MPLS LSP Ping sub-TLVs and follows
   the mechanisms defined in [RFC8029].  All the security considerations
   defined in [RFC8029] will be applicable for this document and, in
   addition, the MPLS LSP Ping sub-TLVs defined in this document do not
   impose any additional security challenges to be considered.

6.  IANA Considerations

   IANA is requested to assign three new sub-TLVs from the "sub-TLVs for
   TLV Types 1, 16, and 21" subregistry of the "Multi-Protocol Label
   Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters"
   registry.

     Sub-Type   Sub-TLV Name                    Reference
     --------   -----------------------------   ------------
      TBD1      SR Policy's Path SID            Section 3.1
      TBD2      SR Candidate Path's Path SID    Section 3.2
      TBD3      SR Segment List's Path SID      Section 3.3

7.  Acknowledgements

   The authors would like to acknowledge Loa Andersson and Detao Zhao
   for their thorough review and very helpful comments.

   The authors would like to acknowledge Yao Liu for the very helpful
   f2f discussion.

8.  References

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8.1.  Normative References

   [I-D.ietf-spring-mpls-path-segment]
              Cheng, W., Li, H., Li, C., Gandhi, R., and R. Zigler,
              "Path Segment Identifier in MPLS Based Segment Routing
              Network", Work in Progress, Internet-Draft, draft-ietf-
              spring-mpls-path-segment-22, 30 November 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-spring-
              mpls-path-segment-22>.

   [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/info/rfc2119>.

   [RFC8029]  Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
              Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
              Switched (MPLS) Data-Plane Failures", RFC 8029,
              DOI 10.17487/RFC8029, March 2017,
              <https://www.rfc-editor.org/info/rfc8029>.

   [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/info/rfc8174>.

   [RFC8287]  Kumar, N., Ed., Pignataro, C., Ed., Swallow, G., Akiya,
              N., Kini, S., and M. Chen, "Label Switched Path (LSP)
              Ping/Traceroute for Segment Routing (SR) IGP-Prefix and
              IGP-Adjacency Segment Identifiers (SIDs) with MPLS Data
              Planes", RFC 8287, DOI 10.17487/RFC8287, December 2017,
              <https://www.rfc-editor.org/info/rfc8287>.

   [RFC8690]  Nainar, N., Pignataro, C., Iqbal, F., and A. Vainshtein,
              "Clarification of Segment ID Sub-TLV Length for RFC 8287",
              RFC 8690, DOI 10.17487/RFC8690, December 2019,
              <https://www.rfc-editor.org/info/rfc8690>.

   [RFC9256]  Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
              A., and P. Mattes, "Segment Routing Policy Architecture",
              RFC 9256, DOI 10.17487/RFC9256, July 2022,
              <https://www.rfc-editor.org/info/rfc9256>.

8.2.  Informative References

   [I-D.ietf-idr-segment-routing-te-policy]
              Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., and
              D. Jain, "Advertising Segment Routing Policies in BGP",
              Work in Progress, Internet-Draft, draft-ietf-idr-segment-

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              routing-te-policy-26, 23 October 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-idr-
              segment-routing-te-policy-26>.

   [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-idr-sr-policy-seglist-id]
              Lin, C., Cheng, W., Liu, Y., Talaulikar, K., and M. Chen,
              "BGP SR Policy Extensions for Segment List Identifier",
              Work in Progress, Internet-Draft, draft-ietf-idr-sr-
              policy-seglist-id-00, 17 December 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-idr-sr-
              policy-seglist-id-00>.

   [I-D.ietf-mpls-sr-epe-oam]
              Hegde, S., Srivastava, M., Arora, K., Ninan, S., and X.
              Xu, "Label Switched Path (LSP) Ping/Traceroute for Segment
              Routing (SR) Egress Peer Engineering Segment Identifiers
              (SIDs) with MPLS Data Planes", Work in Progress, Internet-
              Draft, draft-ietf-mpls-sr-epe-oam-12, 16 January 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-mpls-sr-
              epe-oam-12>.

   [I-D.ietf-pce-multipath]
              Koldychev, M., Sivabalan, S., Saad, T., Beeram, V. P.,
              Bidgoli, H., Yadav, B., Peng, S., and G. S. Mishra, "PCEP
              Extensions for Signaling Multipath Information", Work in
              Progress, Internet-Draft, draft-ietf-pce-multipath-10, 16
              January 2024, <https://datatracker.ietf.org/doc/html/
              draft-ietf-pce-multipath-10>.

   [I-D.ietf-pce-segment-routing-policy-cp]
              Koldychev, M., Sivabalan, S., Barth, C., Peng, S., and H.
              Bidgoli, "PCEP Extensions for SR Policy Candidate Paths",
              Work in Progress, Internet-Draft, draft-ietf-pce-segment-
              routing-policy-cp-13, 16 January 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-pce-
              segment-routing-policy-cp-13>.

   [I-D.ietf-pce-sr-path-segment]
              Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong,
              "Path Computation Element Communication Protocol (PCEP)

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              Extension for Path Segment in Segment Routing (SR)", Work
              in Progress, Internet-Draft, draft-ietf-pce-sr-path-
              segment-08, 24 August 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-pce-sr-
              path-segment-08>.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,
              <https://www.rfc-editor.org/info/rfc3031>.

   [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>.

   [RFC8403]  Geib, R., Ed., Filsfils, C., Pignataro, C., Ed., and N.
              Kumar, "A Scalable and Topology-Aware MPLS Data-Plane
              Monitoring System", RFC 8403, DOI 10.17487/RFC8403, July
              2018, <https://www.rfc-editor.org/info/rfc8403>.

Authors' Addresses

   Xiao Min
   ZTE Corp.
   Nanjing
   China
   Phone: +86 18061680168
   Email: xiao.min2@zte.com.cn

   Shaofu Peng
   ZTE Corp.
   Nanjing
   China
   Email: peng.shaofu@zte.com.cn

   Liyan Gong
   China Mobile
   Beijing
   China
   Email: gongliyan@chinamobile.com

   Rakesh Gandhi
   Cisco Systems, Inc.
   Canada

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   Email: rgandhi@cisco.com

   Carlos Pignataro
   North Carolina State University
   United States of America
   Email: cpignata@gmail.com, cmpignat@ncsu.edu

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