Label Switched Path (LSP) Ping/Traceroute for Segment Routing (SR) Path Segment Identifiers (SIDs) with MPLS Data Planes
draft-xp-mpls-spring-lsp-ping-path-sid-00

Document Type Active Internet-Draft (individual)
Authors Xiao Min  , Shaofu Peng 
Last updated 2020-10-30
Stream (None)
Intended RFC status (None)
Formats plain text xml pdf htmlized (tools) htmlized bibtex
Stream Stream state (No stream defined)
Consensus Boilerplate Unknown
RFC Editor Note (None)
IESG IESG state I-D Exists
Telechat date
Responsible AD (None)
Send notices to (None)
MPLS Working Group                                                X. Min
Internet-Draft                                                 P. Shaofu
Intended status: Standards Track                               ZTE Corp.
Expires: May 3, 2021                                    October 30, 2020

Label Switched Path (LSP) Ping/Traceroute for Segment Routing (SR) Path
            Segment Identifiers (SIDs) with MPLS Data Planes
               draft-xp-mpls-spring-lsp-ping-path-sid-00

Abstract

   Path Segment is a type of 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 May 3, 2021.

Copyright Notice

   Copyright (c) 2020 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.  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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Min & Shaofu               Expires May 3, 2021                  [Page 1]
Internet-Draft       LSP Ping/Trace for SR Path SID         October 2020

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   2
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
     2.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Path Segment ID Sub-TLV . . . . . . . . . . . . . . . . . . .   3
     3.1.  SR Candidate Path's Path SID  . . . . . . . . . . . . . .   3
     3.2.  SR Segment List's Path SID  . . . . . . . . . . . . . . .   6
   4.  Path-SID FEC Validation . . . . . . . . . . . . . . . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

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].

   When 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
   position of Path Segment Label within the MPLS label stack is
   immediately following the segment list of the SR path.  Note that the
   Path Segment would not be popped up until it reaches the egress node.

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

2.  Conventions

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.

Min & Shaofu               Expires May 3, 2021                  [Page 2]
Internet-Draft       LSP Ping/Trace for SR Path SID         October 2020

2.2.  Terminology

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

3.  Path Segment ID Sub-TLV

   Analogous to what's defined in Section 5 of [RFC8287] and Section 4
   of [I-D.ietf-mpls-sr-epe-oam], two 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 Candidate Path's Path SID
         TBD2       SR Segment List's Path SID

   As specified in Section 3 of [I-D.ietf-idr-sr-policy-path-segment],
   the Path Segment can be used to identify an SR path (specified by SID
   list) or an SR candidate path, so two different Target FEC sub-TLVs
   need to be defined for Path Segment ID.  When a Path Segment is used
   to identify an SR path, then the Target FEC sub-TLV of SR Segment
   List'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, then the Target FEC
   sub-TLV of SR Candidate Path's Path SID would be used to validate the
   control plane to forwarding plane synchronization for this Path-SID.

3.1.  SR Candidate Path's Path SID

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

Min & Shaofu               Expires May 3, 2021                  [Page 3]
Internet-Draft       LSP Ping/Trace for SR Path SID         October 2020

    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)                    ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Protocol-Origin|                    Reserved                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                                                               |
   |                  Originator  (20 octets)                      |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Discriminator  (4 octets)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

   Type

      This field is set to the value (TBD1) which indicates that it's a
      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
      [I-D.ietf-spring-segment-routing-policy].  The headend is a
      4-octet IPv4 address or a 16-octet IPv6 address.

   Color

Min & Shaofu               Expires May 3, 2021                  [Page 4]
Internet-Draft       LSP Ping/Trace for SR Path SID         October 2020

      This field associates the SR Policy with an intent, the same as
      defined in Section 2.1 of
      [I-D.ietf-spring-segment-routing-policy].  The color is a 4-octet
      numerical value.

   Endpoint

      This field identifies the endpoint of an SR Policy, the same as
      defined in Section 2.1 of
      [I-D.ietf-spring-segment-routing-policy].  The endpoint is a
      4-octet IPv4 address or a 16-octet IPv6 address.

   Protocol-Origin

      This field identifies the component or protocol that originates or
      signals the candidate path for an SR Policy, the same as defined
      in Section 2.3 of [I-D.ietf-spring-segment-routing-policy].  The
      protocol-origin is a 1-octet value that follows the recommendation
      from Table 1 of Section 2.3 of
      [I-D.ietf-spring-segment-routing-policy], which specifies value 10
      for "PCEP", value 20 for "BGP SR Policy" and value 30 for "Via
      Configuration".

   Originator

      This field identifies the node which provisioned or signaled the
      candidate path for an SR Policy, the same as defined in
      Section 2.4 of [I-D.ietf-spring-segment-routing-policy].  The
      originator is a 20-octet numerical value formed by the
      concatenation of the fields of the tuple <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 "Via
      Configuration", or "PCEP", or "BGP SR Policy", the values of ASN
      and node address follow the specification in Section 2.4 of
      [I-D.ietf-spring-segment-routing-policy].

   Discriminator

      This field uniquely identifies a candidate path within the context
      of an SR policy, the same as defined in Section 2.5 of
      [I-D.ietf-spring-segment-routing-policy].  The discriminator is a
      4-octet value.  When Protocol-Origin is respectively "Via
      Configuration", or "PCEP", or "BGP SR Policy", the value of
      discriminator follows the specification in Section 2.5 of
      [I-D.ietf-spring-segment-routing-policy].

Min & Shaofu               Expires May 3, 2021                  [Page 5]
Internet-Draft       LSP Ping/Trace for SR Path SID         October 2020

3.2.  SR Segment List's Path SID

   The format of SR Segment List's Path SID sub-TLV is as specified
   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)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Segment-List-ID  (4 octets)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 2: SR Segment List's Path SID sub-TLV

   Type

      This field is set to the value (TBD2) which indicates that it's a
      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.

Min & Shaofu               Expires May 3, 2021                  [Page 6]
Internet-Draft       LSP Ping/Trace for SR Path SID         October 2020

   Headend

      This field identifies the headend of an SR Policy, the same as
      defined in Section 2.1 of
      [I-D.ietf-spring-segment-routing-policy].  The headend is a
      4-octet IPv4 address or a 16-octet IPv6 address.

   Color

      This field associates the SR Policy with an intent, the same as
      defined in Section 2.1 of
      [I-D.ietf-spring-segment-routing-policy].  The color is a 4-octet
      numerical value.

   Endpoint

      This field identifies the endpoint of an SR Policy, the same as
      defined in Section 2.1 of
      [I-D.ietf-spring-segment-routing-policy].  The endpoint is a
      4-octet IPv4 address or a 16-octet IPv6 address.

   Protocol-Origin

      This field identifies the component or protocol that originates or
      signals the candidate path for an SR Policy, the same as defined
      in Section 2.3 of [I-D.ietf-spring-segment-routing-policy].  The
      protocol-origin is a 1-octet value that follows the recommendation
      from Table 1 of Section 2.3 of
      [I-D.ietf-spring-segment-routing-policy], which specifies value 10
      for "PCEP", value 20 for "BGP SR Policy" and value 30 for "Via
      Configuration".

   Originator

      This field identifies the node which provisioned or signaled the
      candidate path for an SR Policy, the same as defined in
      Section 2.4 of [I-D.ietf-spring-segment-routing-policy].  The
      originator is a 20-octet numerical value formed by the
      concatenation of the fields of the tuple <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 "Via
      Configuration", or "PCEP", or "BGP SR Policy", the values of ASN
      and node address follow the specification in Section 2.4 of
      [I-D.ietf-spring-segment-routing-policy].

   Discriminator

Min & Shaofu               Expires May 3, 2021                  [Page 7]
Internet-Draft       LSP Ping/Trace for SR Path SID         October 2020

      This field uniquely identifies a candidate path within the context
      of an SR policy, the same as defined in Section 2.5 of
      [I-D.ietf-spring-segment-routing-policy].  The discriminator is a
      4-octet value.  When Protocol-Origin is respectively "Via
      Configuration", or "PCEP", or "BGP SR Policy", the value of
      discriminator follows the specification in Section 2.5 of
      [I-D.ietf-spring-segment-routing-policy].

   Segment-List-ID

      This field identifies an SR path within the context of a candidate
      path of an SR Policy, the same as "List Identifier" defined in
      Section 2.2 of [I-D.lp-idr-sr-path-protection].  The segment-list-
      ID is a 4-octet identifier of the corresponding segment list.

4.  Path-SID FEC Validation

   The MPLS LSP Ping/Traceroute 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 sub-TLV.  The basic length check should be
   performed on the received FEC.

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

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

   If a malformed FEC 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 the 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 Candidate Path's Path SID sub-TLV), {

Min & Shaofu               Expires May 3, 2021                  [Page 8]
Internet-Draft       LSP Ping/Trace for SR Path SID         October 2020

         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:

         +  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 10, "PCEP" is used
               as the signaling protocol.  And then validate that the
               Path Segment ID matches with the tuples identifying the
               SR Candidate Path within PCEP {

               o  Validate that the signaled headend 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 headend field in the received SR
                  Candidate Path's Path SID sub-TLV.

               o  Validate that the signaled color 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 color field in the received SR
                  Candidate Path's Path SID sub-TLV.

               o  Validate that the signaled end-point 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 endpoint field in the received SR
                  Candidate Path's Path SID sub-TLV.

               o  Validate that the signaled both originator ASN and
                  originator address 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 originator field in the received SR
                  Candidate Path's Path SID sub-TLV.

               o  Validate that the signaled 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 discriminator field 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 20, "BGP SR Policy"

Min & Shaofu               Expires May 3, 2021                  [Page 9]
Internet-Draft       LSP Ping/Trace for SR Path SID         October 2020

               is used as the signaling protocol.  And then validate
               that the Path Segment ID matches with the tuples
               identifying the SR Candidate Path within BGP SR Policy {

               o  Validate that the signaled headend 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 headend field in the received SR
                  Candidate Path's Path SID sub-TLV.

               o  Validate that the signaled policy color 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 color field in the received SR
                  Candidate Path's Path SID sub-TLV.

               o  Validate that the signaled endpoint 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 endpoint field in the received
                  SR Candidate Path's Path SID sub-TLV.

               o  Validate that the signaled both ASN and BGP Router-ID
                  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 originator field in the
                  received SR Candidate Path's Path SID sub-TLV.

               o  Validate that the signaled 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 discriminator field 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 30, "Via
               Configuration" is used.  And then validate that the Path
               Segment ID matches with the tuples identifying the SR
               Candidate Path within Configuration {

               o  Validate that the provisioned headend defined in
                  [I-D.ietf-spring-sr-policy-yang], for the Path SID,
                  matches with the headend field in the received SR
                  Candidate Path's Path SID sub-TLV.

Min & Shaofu               Expires May 3, 2021                 [Page 10]
Internet-Draft       LSP Ping/Trace for SR Path SID         October 2020

               o  Validate that the provisioned color defined in
                  [I-D.ietf-spring-sr-policy-yang], for the Path SID,
                  matches with the color field in the received SR
                  Candidate Path's Path SID sub-TLV.

               o  Validate that the provisioned endpoint defined in
                  [I-D.ietf-spring-sr-policy-yang], for the Path SID,
                  matches with the endpoint field in the received SR
                  Candidate Path's Path SID sub-TLV.

               o  Validate that the provisioned originator defined in
                  [I-D.ietf-spring-sr-policy-yang], for the Path SID,
                  matches with the originator field in the received SR
                  Candidate Path's Path SID sub-TLV.

               o  Validate that the provisioned discriminator defined in
                  [I-D.ietf-spring-sr-policy-yang], for the Path SID,
                  matches with the discriminator field 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 TBD2 (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:

         +  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 10, "PCEP" is used as the
               signaling protocol.  And then validate that the Path
               Segment ID matches with the tuples identifying the SR
               Segment List within PCEP {

Min & Shaofu               Expires May 3, 2021                 [Page 11]
Internet-Draft       LSP Ping/Trace for SR Path SID         October 2020

               o  Validate that the signaled headend 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 headend field in the received SR
                  Segment List's Path SID sub-TLV.

               o  Validate that the signaled color 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 color field in the received SR
                  Segment List's Path SID sub-TLV.

               o  Validate that the signaled end-point 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 endpoint field in the received SR
                  Segment List's Path SID sub-TLV.

               o  Validate that the signaled both originator ASN and
                  originator address 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 originator field in the received SR
                  Segment List's Path SID sub-TLV.

               o  Validate that the signaled 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 discriminator field in the received
                  SR Segment List's Path SID sub-TLV.

               o  Validate that the signaled Segment-List-ID by PCEP,
                  for the Path SID, matches with the Segment-List-ID
                  field 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 20, "BGP SR Policy" is used as
               the signaling protocol.  And then validate that the Path
               Segment ID matches with the tuples identifying the SR
               Segment List within BGP SR Policy {

               o  Validate that the signaled headend defined in
                  [I-D.ietf-idr-segment-routing-te-policy] and
                  [I-D.ietf-idr-sr-policy-path-segment], for the Path

Min & Shaofu               Expires May 3, 2021                 [Page 12]
Internet-Draft       LSP Ping/Trace for SR Path SID         October 2020

                  SID, matches with the headend field in the received SR
                  Segment List's Path SID sub-TLV.

               o  Validate that the signaled policy color 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 color field in the received SR
                  Segment List's Path SID sub-TLV.

               o  Validate that the signaled endpoint 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 endpoint field in the received
                  SR Segment List's Path SID sub-TLV.

               o  Validate that the signaled both ASN and BGP Router-ID
                  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 originator field in the
                  received SR Segment List's Path SID sub-TLV.

               o  Validate that the signaled 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 discriminator field in the
                  received SR Segment List's Path SID sub-TLV.

               o  Validate that the signaled List Identifier defined in
                  [I-D.lp-idr-sr-path-protection], for the Path SID,
                  matches with the Segment-List-ID field 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 30, "Via Configuration" is
               used.  And then validate that the Path Segment ID matches
               with the tuples identifying the SR Segment List within
               Configuration {

               o  Validate that the provisioned headend defined in
                  [I-D.ietf-spring-sr-policy-yang], for the Path SID,
                  matches with the headend field in the received SR
                  Segment List's Path SID sub-TLV.

               o  Validate that the provisioned color defined in
                  [I-D.ietf-spring-sr-policy-yang], for the Path SID,

Min & Shaofu               Expires May 3, 2021                 [Page 13]
Internet-Draft       LSP Ping/Trace for SR Path SID         October 2020

                  matches with the color field in the received SR
                  Segment List's Path SID sub-TLV.

               o  Validate that the provisioned endpoint defined in
                  [I-D.ietf-spring-sr-policy-yang], for the Path SID,
                  matches with the endpoint field in the received SR
                  Segment List's Path SID sub-TLV.

               o  Validate that the provisioned originator defined in
                  [I-D.ietf-spring-sr-policy-yang], for the Path SID,
                  matches with the originator field in the received SR
                  Segment List's Path SID sub-TLV.

               o  Validate that the provisioned discriminator defined in
                  [I-D.ietf-spring-sr-policy-yang], for the Path SID,
                  matches with the discriminator field in the received
                  SR Segment List's Path SID sub-TLV.

               o  Validate that the provisioned Segment-List-ID through
                  Yang Model, for the Path SID, matches with the
                  Segment-List-ID field 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 does not raise any additional security issues beyond
   those of the specifications referred to in the list of normative
   references.

6.  IANA Considerations

   IANA is requested to assign two 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 [IANA].

Min & Shaofu               Expires May 3, 2021                 [Page 14]
Internet-Draft       LSP Ping/Trace for SR Path SID         October 2020

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

7.  Acknowledgements

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

8.  References

8.1.  Normative References

   [I-D.ietf-spring-mpls-path-segment]
              Cheng, W., Li, H., Chen, M., Gandhi, R., and R. Zigler,
              "Path Segment in MPLS Based Segment Routing Network",
              draft-ietf-spring-mpls-path-segment-03 (work in progress),
              September 2020.

   [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>.

Min & Shaofu               Expires May 3, 2021                 [Page 15]
Internet-Draft       LSP Ping/Trace for SR Path SID         October 2020

8.2.  Informative References

   [I-D.ietf-idr-segment-routing-te-policy]
              Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P.,
              Rosen, E., Jain, D., and S. Lin, "Advertising Segment
              Routing Policies in BGP", draft-ietf-idr-segment-routing-
              te-policy-09 (work in progress), May 2020.

   [I-D.ietf-idr-sr-policy-path-segment]
              Li, C., Li, Z., Telecom, C., Cheng, W., and K. Talaulikar,
              "SR Policy Extensions for Path Segment and Bidirectional
              Path", draft-ietf-idr-sr-policy-path-segment-01 (work in
              progress), August 2020.

   [I-D.ietf-mpls-sr-epe-oam]
              Hegde, S., Arora, K., Srivastava, M., 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", draft-ietf-mpls-sr-epe-
              oam-00 (work in progress), June 2020.

   [I-D.ietf-pce-segment-routing-policy-cp]
              Koldychev, M., Sivabalan, S., Barth, C., Peng, S., and H.
              Bidgoli, "PCEP extension to support Segment Routing Policy
              Candidate Paths", draft-ietf-pce-segment-routing-policy-
              cp-01 (work in progress), October 2020.

   [I-D.ietf-pce-sr-path-segment]
              Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong,
              "Path Computation Element Communication Protocol (PCEP)
              Extension for Path Segment in Segment Routing (SR)",
              draft-ietf-pce-sr-path-segment-01 (work in progress), May
              2020.

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
              P. Mattes, "Segment Routing Policy Architecture", draft-
              ietf-spring-segment-routing-policy-08 (work in progress),
              July 2020.

   [I-D.ietf-spring-sr-policy-yang]
              Raza, K., Sawaya, R., Shunwan, Z., Voyer, D., Durrani, M.,
              Matsushima, S., and V. Beeram, "YANG Data Model for
              Segment Routing Policy", draft-ietf-spring-sr-policy-
              yang-00 (work in progress), September 2020.

Min & Shaofu               Expires May 3, 2021                 [Page 16]
Internet-Draft       LSP Ping/Trace for SR Path SID         October 2020

   [I-D.lp-idr-sr-path-protection]
              Yao, L. and S. Peng, "BGP extensions of SR policy for path
              protection", draft-lp-idr-sr-path-protection-00 (work in
              progress), October 2020.

   [IANA]     Internet Assigned Numbers Authority (IANA), "Multi-
              Protocol Label Switching (MPLS) Label Switched Paths
              (LSPs) Ping Parameters", <http://www.iana.org/assignments/
              mpls-lsp-ping-parameters>.

   [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

   Email: xiao.min2@zte.com.cn

   Peng Shaofu
   ZTE Corp.
   Nanjing
   China

   Email: peng.shaofu@zte.com.cn

Min & Shaofu               Expires May 3, 2021                 [Page 17]