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-11

Routing area                                                    S. Hegde
Internet-Draft                                             M. Srivastava
Intended status: Standards Track                   Juniper Networks Inc.
Expires: 10 March 2024                                          K. Arora
                                                                S. Ninan
                                                  Individual Contributor
                                                                   X. Xu
                                                            China Mobile
                                                        7 September 2023

   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-11

Abstract

   Egress Peer Engineering (EPE) is an application of Segment Routing to
   solve the problem of egress peer selection.  The Segment Routing
   based BGP-EPE solution allows a centralized controller, e.g. a
   Software Defined Network (SDN) controller to program any egress peer.
   The EPE solution requires a node to program the PeerNode Segment
   Identifier(SID) describing a session between two nodes, the PeerAdj
   SID describing the link (one or more) that is used by sessions
   between peer nodes, and the PeerSet SID describing an arbitrary set
   of sessions or links between a local node and its peers.  This
   document provides new sub-TLVs for EPE Segment Identifiers (SID) that
   would be used in the MPLS Target stack TLV (Type 1), in MPLS Ping and
   Traceroute procedures.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on 10 March 2024.

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Copyright Notice

   Copyright (c) 2023 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/
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Theory of Operation . . . . . . . . . . . . . . . . . . . . .   3
   3.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   4.  FEC Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  PeerAdj SID Sub-TLV . . . . . . . . . . . . . . . . . . .   4
     4.2.  PeerNode SID Sub-TLV  . . . . . . . . . . . . . . . . . .   6
     4.3.  PeerSet SID Sub-TLV . . . . . . . . . . . . . . . . . . .   8
   5.  EPE-SID FEC validation  . . . . . . . . . . . . . . . . . . .  10
     5.1.  EPE-SID FEC validiation . . . . . . . . . . . . . . . . .  11
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  13
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   Egress Peer Engineering (EPE) as defined in [RFC9087] is an effective
   mechanism to select the egress peer link based on different criteria.
   In this scenario, egress peers may belong to a completely different
   administration.  The EPE-SIDs provide means to represent egress peer
   nodes, links set of links and set of nodes.  Many network deployments
   have built their networks consisting of multiple Autonomous Systems,
   either for the ease of operations or as a result of network mergers
   and acquisitons.  The inter-AS links connecting any two Autonomous
   Systems could be traffic engineered using EPE-SIDs in this case,
   where there is single ownership but different AS numbers.  It is
   important to be able to validate the control plane to forwarding
   plane synchronization for these SIDs so that any anomaly can be
   detected easily by the operator.

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      +---------+      +------+
      |         |      |      |
      |    H    B------D      G
      |         | +---/| AS 2 |\  +------+
      |         |/     +------+ \ |      |---L/8
      A   AS1   C---+            \|      |
      |         |\\  \  +------+ /| AS 4 |---M/8
      |         | \\  +-E      |/ +------+
      |    X    |  \\   |      K
      |         |   +===F AS 3 |
      +---------+       +------+

                        Figure 1: Reference Diagram

   In this reference diagram, EPE-SIDs are advertised from AS1 to AS2
   and AS3.  In certain cases the EPE-SIDs advertised by the control
   plane may not be in synchronization with the label programmed in the
   data-plane.  For example, on C a PeerAdj SID could be advertised to
   indicate it is for the link C->D.  Due to some software anomaly the
   actual data forwarding on this PeerAdj SID could be happening over
   the C->E link.  If E had relevant data paths for further forwarding
   the packet, this kind of anomalies will go unnoticed by the operator.
   A FEC definition for the EPE-SIDs will define the details of the
   control plane association of the SID.  The data plane validation of
   the SID will be done during the MPLS trace route procedure.  When
   there is a multi-hop EBGP session between the ASBRs, PeerNode SID is
   advertised and the traffic MAY be load-balanced between the
   interfaces connecting the two nodes.  In the reference diagram C and
   F could have a PeerNode-SID advertised.  When the OAM packet is
   received on F, it needs to validate that the packet came on one of
   the two interfaces connected to C.

   This document provides Target Forwarding Equivalence Class (FEC)
   stack TLV definitions for EPE-SIDs.  This solution requires that the
   node constructing the target FEC stack is able to determine the type
   of the SIDs along the path of the LSP.  Other procedures for MPLS
   Ping and Traceroute as defined in [RFC8287] section 7 and clarified
   by [RFC8690] are applicable for EPE-SIDs as well.

2.  Theory of Operation

   [RFC9086] provides mechanisms to advertise the EPE-SIDs in BGP-LS.
   These EPE-SIDs may be used to build Segment Routing paths as
   described in [I-D.ietf-idr-segment-routing-te-policy] or using Path
   Computation Element Protocol (PCEP) extensions as defined in
   [RFC8664].  Data plane monitoring for such paths which consist of
   EPE-SIDs will use extensions defined in this document to build the

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   Target FEC stack TLV.  The MPLS Ping and Traceroute procedures MAY be
   initiated by the head-end of the Segment Routing path or a
   centralized topology-aware data plane monitoring system as described
   in [RFC8403].  The extensions in
   [I-D.ietf-idr-segment-routing-te-policy] and [RFC8664] do not define
   how to carry the details of the SID that can be used to construct the
   FEC.  Such extensions are out of scope for this document.  The node
   initiating the data plane monitoring may acquire the details of EPE-
   SIDs through BGP-LS advertisements as described in [RFC9086].  There
   may be other possible mechanisms to learn the definition of the SID
   from controller.  Details of such mechanisms are out of scope for
   this document.

   The EPE-SIDs are advertised for inter-AS links which run EBGP
   sessions.  [RFC9086] does not define the detailed procedures to
   operate EBGP sessions in a scenario with unnumbered interfaces.
   Therefore, these scenarios are out of scope for this document.
   During AS migration scenario procedures described in [RFC7705] may be
   in force.  In these scenarios, if the local and remote AS fields in
   the FEC as described in Section 4 carries the globally configured ASN
   and not the "local AS" as defined in [RFC7705], the FEC validation
   procedures may fail.

3.  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.

4.  FEC Definitions

   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      PeerAdj SID Sub-TLV
                TBD2      PeerNode SID Sub-TLV
                TBD3      PeerSet SID Sub-TLV

                        Figure 2: New sub-TLV types

4.1.  PeerAdj SID Sub-TLV

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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               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |               Local AS Number (4  octets)                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote AS Number (4 octets)                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Local BGP router ID (4 octets)                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote BGP Router ID (4 octets)                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Local Interface address (4/16 octets)            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote Interface address (4/16 octets)           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 3: PeerAdj SID Sub-TLV

   Type : TBD1

   Length : variable based on IPV4/IPV6 interface address.  Length
   excludes the length of Type and Length field.For IPV4 interface
   addresses length will be 24.  In case of IPV6 address length will be
   48.

   Local AS Number :

   4 octet unsigned integer representing the Member-AS Number inside the
   Confederation [RFC5065].  The AS number corresponds to the AS to
   which PeerAdj SID advertising node belongs to.

   Remote AS Number :

   4 octet unsigned integer representing the Member-AS Number inside the
   Confederation [RFC5065].  The AS number corresponds to the AS of the
   remote node for which the PeerAdj SID is advertised.

   Local BGP Router ID :

   4 octet unsigned integer of the advertising node representing the BGP
   Identifier as defined in [RFC4271] and [RFC6286].

   Remote BGP Router ID :

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   4 octet unsigned integer of the receiving node representing the BGP
   Identifier as defined in [RFC4271] and [RFC6286].

   Local Interface Address :

   In case of PeerAdj SID, Local interface address corresponding to the
   PeerAdj SID should be specified in this field.  For IPV4,this field
   is 4 octets; for IPV6, this field is 16 octets.  Link Local IPV6
   addresses are for further study.

   Remote Interface Address :

   In case of PeerAdj SID Remote interface address corresponding to the
   PeerAdj SID should be apecified in this field.  For IPV4, this field
   is 4 octets; for IPV6, this field is 16 octets.  Link Local IPv6
   addresses are for further study.

   [RFC9086] mandates sending local interface ID and remote interface ID
   in the Link Descriptors and allows a value of 0 in the remote
   descriptors.  It is useful to validate the incoming interface for a
   OAM packet and if the remote descriptor is 0 this validation is not
   possible.  [RFC9086] allows optional link descriptors of local and
   remote interface addresses as described in section 4.2.  This
   document RECOMMENDs sending these optional descriptors and using them
   to validate incoming interface.  When these local and remote
   interface addresses are not available, an ingress node can send 0 in
   the local and/or remote interface address field.  The receiver SHOULD
   skip the validation for the incoming interface if the address field
   contains 0.

4.2.  PeerNode SID Sub-TLV

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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 = TBD2                    |          Length               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |               Local AS Number (4  octets)                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote AS Number (4 octets)                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Local BGP router ID (4 octets)                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote BGP Router ID (4 octets)                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 4: PeerNode SID Sub-TLV

   Type : TBD2

   Length : 16

   Local AS Number :

   4 octet unsigned integer representing the Member-AS Number inside the
   Confederation [RFC5065].  The AS number corresponds to the AS to
   which PeerNode SID advertising node belongs to.

   Remote AS Number :

   4 octet unsigned integer representing the Member-AS Number inside the
   Confederation [RFC5065].  The AS number corresponds to the AS of the
   remote node for which the PeerNode SID is advertised.

   Local BGP Router ID :

   4 octet unsigned integer of the advertising node representing the BGP
   Identifier as defined in [RFC4271] and [RFC6286].

   Remote BGP Router ID :

   4 octet unsigned integer of the receiving node representing the BGP
   Identifier as defined in [RFC4271] and [RFC6286].

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   When there is a multi-hop EBGP session between two ASBRs, PeerNode
   SID is advertised for this session and traffic can be load balanced
   across these interfaces.  An EPE controller that does bandiwdth
   management for these links should be aware of the links on which the
   traffic will be load-balanced.  As per [RFC8029], the node
   advertising the EPE SIDs will send Downstream Detailed Mapping TLV
   (DDMAP TLV) specifying the details of nexthop interfaces, the OAM
   packet will be sent out.  Based on this information controller MAY
   choose to verify the actual forwarding state with the topology
   information controller has.  On the router, the validation procedures
   will include, received DDMAP validation as specified in [RFC8029] to
   verify the control and forwarding state synchronization on the two
   routers.  Any descrepancies between controller's state and forwarding
   state will not be detected by the procedures described in the
   document.

4.3.  PeerSet SID Sub-TLV

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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               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Local AS Number (4  octets)                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Local BGP router ID (4 octets)                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   No.of elements in set       |          Reserved             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote AS Number (4 octets)                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote BGP Router ID (4 octets)                  |
       ++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++

        One element in set consists of below details
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote AS Number (4 octets)                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Remote BGP Router ID (4 octets)                  |
       ++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++

                    Figure 5: PeerSet SID Sub-TLV

   Type : TBD3

   Length : variable based on the number of elements in the set.  The
   length field does not include the length of Type and Length fields.

   Local AS Number :

   4 octet unsigned integer representing the Member-AS Number inside the
   Confederation.[RFC5065].  The AS number corresponds to the AS to
   which PeerSet SID advertising node belongs to.

   Remote AS Number :

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   4 octet unsigned integer representing the Member-AS Number inside the
   Confederation [RFC5065].  The AS number corresponds to the AS of the
   remote node for which the PeerSet SID is advertised.

   Advertising BGP Router ID :

   4 octet unsigned integer of the advertising node representing the BGP
   Identifier as defined in [RFC4271] and [RFC6286].

   Receiving BGP Router ID :

   4 octet unsigned integer of the receiving node representing the BGP
   Identifier as defined in [RFC4271] and [RFC6286].

   No.of elements in set:

   Number of remote ASes, the set SID load-balances on.

   PeerSet SID may be associated with a number of PeerNode SIDs and
   PeerAdj SIDs.  The remote AS number and the Router ID of each of
   these PeerNode SIDs PeerAdj SIDs MUST be included in the FEC.

5.  EPE-SID FEC validation

   When a remote ASBR of the EPE-SID advertisement receives the MPLS OAM
   packet with top FEC being the EPE-SID, it SHOULD perform validity
   checks on the content of the EPE-SID FEC sub-TLV.  The basic length
   check should be performed on the received FEC.

    PeerAdj SID
    -----------
    Length = 24 or 48

    Peer Node SID
    -------------
    Length = 20 + No.of IPv4 interface pairs * 8 +
             No.of IPv6 interface pairs * 32

    PeerSet SID
    -----------
    Length = 9 + no.of elements in the set *
             (8 + No.of IPv4 interface pairs * 8 +
              No.of IPv6 interface pairs * 32)

                        Figure 6: Length Validation

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   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]

5.1.  EPE-SID FEC validiation

   4a.  Segment Routing IGP-Prefix, IGP-Adjacency SID and EPE-SID
   Validation :

   If the Label-stack-depth is 0 and the Target FEC Stack sub-TLV at
   FEC-stack-depth is TBD1 (PeerAdj SID sub-TLV)

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

      o Validate that the Receiving Node BGP Local AS matches with the
      remote AS field in the received PeerAdj SID FEC sub-TLV.

      o Validate that the Receiving Node BGP Router-ID matches with the
      Remote Router ID field in the received PeerAdj SID FEC.

      o Validate that there is a EBGP session with a peer having local
      AS number and BGP Router-ID as specified in the Local AS number
      and Local Router-ID field in the received PeerAdj SID FEC sub-TLV.

   If the Remote interface address is not zero, validate the incoming
   interface.  Set the Best-return-code to 35 "Mapping for this FEC is
   not associated with the incoming interface" [RFC8287] if any below
   conditions fail:

      o Validate the incoming interface on which the OAM packet was
      receieved, matches with the remote interface specified in the
      PeerAdj SID FEC sub-TLV

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

   Else, if the Target FEC sub-TLV at FEC-stack-depth is TBD2 (PeerNode
   SID sub-TLV),

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

      o Validate that the Receiving Node BGP Local AS matches with the
      remote AS field in the received PeerNode SID FEC sub-TLV.

      o Validate that the Receiving Node BGP Router-ID matches with the
      Remote Router ID field in the received PeerNode SID FEC.

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      o Validate that there is a EBGP session with a peer having local
      AS number and BGP Router-ID as specified in the Local AS number
      and Local Router-ID field in the received PeerNode SID FEC sub-
      TLV.

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

   Else, if the Target FEC sub-TLV at FEC-stack-depth is TBD3 (PeerSet
   SID sub-TLV),

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

      o Validate that the Receiving Node BGP Local AS matches with one
      of the remote AS field in the received PeerSet SID FEC sub-TLV.

      o Validate that the Receiving Node BGP Router-ID matches with one
      of the Remote Router ID field in the received PeerSet SID FEC sub-
      TLV.

      o Validate that there is a EBGP session with a peer having local
      AS number and BGP Router-ID as specified in the Local AS number
      and Local Router-ID field in the received PeerSet SID FEC sub-TLV.

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

6.  IANA Considerations

   IANA is requested to allocated three new Target FEC stack sub-TLVs
   from the "Sub-TLVs for TLV types 1,16 and 21" subregistry in the
   "TLVs" registry of the "Multi-Protocol Label switching (MPLS) Label
   Switched Paths (LSPs) Ping parameters" namespace.

      PeerAdj SID Sub-TLV : TBD1

      PeerNode SID Sub-TLV: TBD2

      PeerSet SID Sub-TLV : TBD3

   The three lowest free values from the Standard Tracks range should be
   allocated if possible.

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7.  Security Considerations

   The EPE-SIDs are advertised for egress links for Egress Peer
   Engineering purposes or for inter-AS links between co-operating ASes.
   When co-operating domains are involved, they can allow the packets
   arriving on trusted interfaces to reach the control plane and get
   processed.  When EPE-SIDs which are created for egress TE links where
   the neighbor AS is an independent entity, it may not allow packets
   arriving from external world to reach the control plane.  In such
   deployments MPLS OAM packets will be dropped by the neighboring AS
   that receives the MPLS OAM packet.  In MPLS traceroute applications,
   when the AS boundary is crossed with the EPE-SIDs, the FEC stack is
   changed.  [RFC8287] does not mandate that the initiator upon
   receiving an MPLS Echo Reply message that includes the FEC Stack
   Change TLV with one or more of the original segments being popped
   remove a corresponding FEC(s) from the Target FEC Stack TLV in the
   next (TTL+1) traceroute request.  If an initiator does not remove the
   FECs belonging to the previous AS that has traversed, it MAY expose
   the internal AS information to the following AS being traversed in
   traceroute.

8.  Acknowledgments

   Thanks to Loa Andersson, Dhruv Dhody, Ketan Talaulikar, Italo Busi
   and Alexander Vainshtein, Deepti Rathi for careful review and
   comments.

9.  References

9.1.  Normative References

   [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>.

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   [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>.

   [RFC9086]  Previdi, S., Talaulikar, K., Ed., Filsfils, C., Patel, K.,
              Ray, S., and J. Dong, "Border Gateway Protocol - Link
              State (BGP-LS) Extensions for Segment Routing BGP Egress
              Peer Engineering", RFC 9086, DOI 10.17487/RFC9086, August
              2021, <https://www.rfc-editor.org/info/rfc9086>.

9.2.  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-
              routing-te-policy-23, 25 July 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-idr-
              segment-routing-te-policy-23>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [RFC5065]  Traina, P., McPherson, D., and J. Scudder, "Autonomous
              System Confederations for BGP", RFC 5065,
              DOI 10.17487/RFC5065, August 2007,
              <https://www.rfc-editor.org/info/rfc5065>.

   [RFC6286]  Chen, E. and J. Yuan, "Autonomous-System-Wide Unique BGP
              Identifier for BGP-4", RFC 6286, DOI 10.17487/RFC6286,
              June 2011, <https://www.rfc-editor.org/info/rfc6286>.

   [RFC7705]  George, W. and S. Amante, "Autonomous System Migration
              Mechanisms and Their Effects on the BGP AS_PATH
              Attribute", RFC 7705, DOI 10.17487/RFC7705, November 2015,
              <https://www.rfc-editor.org/info/rfc7705>.

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   [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>.

   [RFC8664]  Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "Path Computation Element Communication
              Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
              DOI 10.17487/RFC8664, December 2019,
              <https://www.rfc-editor.org/info/rfc8664>.

   [RFC9087]  Filsfils, C., Ed., Previdi, S., Dawra, G., Ed., Aries, E.,
              and D. Afanasiev, "Segment Routing Centralized BGP Egress
              Peer Engineering", RFC 9087, DOI 10.17487/RFC9087, August
              2021, <https://www.rfc-editor.org/info/rfc9087>.

   [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>.

Authors' Addresses

   Shraddha Hegde
   Juniper Networks Inc.
   Exora Business Park
   Bangalore 560103
   KA
   India
   Email: shraddha@juniper.net

   Mukul Srivastava
   Juniper Networks Inc.
   Email: msri@juniper.net

   Kapil Arora
   Individual Contributor
   Email: kapil.it@gmail.com

   Samson Ninan
   Individual Contributor
   Email: samson.cse@gmail.com

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   Xiaohu Xu
   China Mobile
   Beijing
   China
   Email: xuxiaohu_ietf@hotmail.com

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