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<rfc xmlns:xi="http://www.w3.org/2001/XInclude" category="std" docName="draft-ietf-mpls-sr-epe-oam-19" ipr="trust200902"> number="9703" consensus="true" ipr="trust200902" obsoletes="" updates="" submissionType="IETF" xml:lang="en" tocInclude="true" tocDepth="3" symRefs="true" sortRefs="true" version="3">

  <front>
    <title abbrev="EPE-OAM">Label abbrev="LSP Ping/Traceroute for SR EPE-SIDs with MPLS">Label Switched Path (LSP) Ping/Traceroute for
    Segment Routing (SR) Egress Peer Engineering (EPE) Segment Identifiers (SIDs)
    with MPLS Data Plane</title>
    <seriesInfo name="RFC" value="9703"/>
    <author initials="S." surname="Hegde" fullname="Shraddha Hegde">
      <organization>Juniper Networks Inc.</organization>
      <address>
        <postal>
          <street>Exora Business Park</street>
          <city>Bangalore</city>
        <region>KA</region>
          <region>Karnataka</region>
          <code>560103</code>
          <country>India</country>
        </postal>
        <email>shraddha@juniper.net</email>
      </address>
    </author>
    <author initials="M." surname="Srivastava" fullname="Mukul Srivastava">
      <organization>Juniper Networks Inc.</organization>
      <address>
      <postal>
        <street></street>
        <city></city>
        <region></region>
        <code></code>
        <country></country>
      </postal>
        <email>msri@juniper.net</email>
      </address>
    </author>
    <author initials="K." surname="Arora" fullname="Kapil Arora">
      <organization>Individual Contributor</organization>
      <address>
      <postal>
        <street></street>
        <city></city>
        <region></region>
        <code></code>
        <country></country>
      </postal>
        <email>kapil.it@gmail.com</email>
      </address>
    </author>
    <author initials="S." surname="Ninan" fullname="Samson Ninan">
      <organization>Ciena</organization>
      <address>
      <postal>
        <street></street>
        <city></city>
        <region></region>
        <code></code>
        <country></country>
      </postal>
        <email>samson.cse@gmail.com</email>
      </address>
    </author>
    <author initials="X." surname="Xu" fullname="Xiaohu Xu">
      <organization>China Mobile</organization>
      <address>
        <postal>
        <street></street>
          <city>Beijing</city>
        <region></region>
        <code></code>
          <country>China</country>
        </postal>
        <email>xuxiaohu_ietf@hotmail.com </email>
      </address>
    </author>
    <date year="2024"/>
  <area>Routing</area>
  <workgroup>Routing area</workgroup> year="2024" month="December"/>
    <area>RTG</area>
    <workgroup>mpls</workgroup>
    <keyword>OAM</keyword>
    <keyword>EPE</keyword>
    <keyword>BGP-LS</keyword>
    <keyword>BGP</keyword>
    <keyword>SPRING</keyword>
    <keyword>SDN</keyword>
    <keyword>SID</keyword>
    <abstract>
      <t>Egress Peer Engineering (EPE) is an application of Segment Routing to
   solve
      (SR) that solves the problem of egress peer selection.  The Segment Routing based SR-based
      BGP-EPE solution allows a centralized controller, e.g. e.g., a Software
   Defined
      Software-Defined Network (SDN) controller controller, to program any egress peer.
      The EPE solution requires the node or the SDN controller to program 1) the
      PeerNode Segment
   Identifier(SID) Identifier (SID) describing a session between two
      nodes, 2) the PeerAdj SID sub-TLV describing the link (one or more) links that is are
      used by the sessions between peer nodes, and 3) the PeerSet SID
      describing any connected interface to any peer in the related group.
      This document provides new sub-TLVs for EPE Segment
   Identifiers (SID) EPE-SIDs that would be are used in
      the MPLS Target stack FEC Stack TLV (Type 1), 1) in MPLS Ping and Traceroute procedures.

 </t>
      procedures.</t>
    </abstract>
  </front>
  <middle>
    <section title="Introduction" anchor='intro'> anchor="intro" numbered="true" toc="default">
      <name>Introduction</name>
      <t> Egress Peer Engineering (EPE) (EPE), as defined in <xref target ='RFC9087'/> target="RFC9087"
      format="default"/>, is an effective mechanism that is used to select the egress peer
      link based on different criteria.  In this scenario, egress peers may
      belong to a completely different ownership.  The EPE-SIDs provide the
      means to represent egress peer nodes, links, sets of links links, and sets of
      nodes. Many network deployments have built their networks consisting of
      multiple Autonomous
Systems, Systems (ASes) either for the ease of operations or as a
      result of network mergers and acquisitions. The inter-AS links
      connecting any two Autonomous Systems ASes could be traffic-engineered using
      EPE-SIDs in this case, where there is single ownership but different
      AS numbers.  It is important to validate the control
      plane to forwarding plane synchronization for these SIDs so that any
      anomaly can be detected easily detected by the network operator. EPE-SIDs may
      also be used in an ingress SR Segment Routing (SR) policy <xref target ='RFC9256'/>to target="RFC9256"
      format="default"/> to choose exit points where the remote AS belongs to has
      a completely different ownership. This scenario is out of scope of for this
      document.
      </t>
 <t>
      <figure anchor="reference_diagram" title="Reference Diagram">
      <artwork> anchor="reference_diagram">
        <name>Reference Diagram</name>
        <artwork name="" type="" align="left" alt=""><![CDATA[
   +---------+      +------+
   |         |      |      |
   |    H    B------D      G
   |         | +---/| AS 2 AS2  |\  +------+
   |         |/     +------+ \ |      |---L/8
   A   AS1   C---+            \|      |
   |         |\\  \  +------+ /| AS 4 AS4  |---M/8
   |         | \\  +-E      |/ +------+
   |    X    |  \\   |      K
   |         |   +===F AS 3 AS3  |
   +---------+       +------+

    </artwork>       +------+]]></artwork>
      </figure>
    In this reference diagram,
      <t>In <xref target="reference_diagram" format="default"/>, EPE-SIDs are
      configured on AS1 towards AS2 and AS3 and advertised in BGP-LS the Border
      Gateway Protocol - Link State (BGP-LS) <xref target="RFC9086"/>. target="RFC9086"
      format="default"/>.  In certain cases 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 C, a PeerAdj SID could be advertised to
      indicate it is for the link C->D. C-&gt;D.  Due to some software anomaly, the
      actual data forwarding on this PeerAdj SID could be happening over the C->E
      C-&gt;E link.  If E had relevant data paths for further forwarding the
      packet, this kind of anomaly will would go unnoticed by the network operator.
      A detailed example of a correctly programmed state and an incorrectly
      programmed state along with a description of how the incorrect state can
      be detected is described in <xref target="APPENDIX"/>. target="Appendix" format="default"/>.
      A FEC Forwarding Equivalence Class (FEC) definition for the EPE-SIDs will define the details of
      detail the control plane association of the SID.  The
      data plane validation of the SID will be done during the MPLS traceroute Traceroute
      procedure.  When there is a multi-hop EBGP External BGP (EBGP) session
      between the ASBRs, a PeerNode SID is advertised, and the traffic MAY
      <bcp14>MAY</bcp14> be load-balanced between the interfaces connecting
      the two nodes.  In the reference
    diagram, <xref target="reference_diagram" format="default"/>,
      C and F could have a PeerNode-SID PeerNode SID advertised.  When the OAM Operations,
      Administration, and Maintenance (OAM) packet is received on F, it needs
      to be validated that the packet came from one of the two interfaces
      connected to C.
      </t>
      <t> This document provides Target Forwarding Equivalence Class (FEC)
 stack
      Stack TLV definitions for EPE-SIDs.  This solution requires that the
      node constructing the target Target FEC stack can Stack TLV to determine the type types of the
      SIDs along the path of the LSP. Other procedures for MPLS Ping and Traceroute
      Traceroute, as defined in <xref target="RFC8287"/> section 7 target="RFC8287" sectionFormat="of"
      section="7"/> and clarified by in <xref target="RFC8690"/> target="RFC8690" format="default"/>,
      are applicable for EPE-SIDs as well.</t>
    </section>
    <section title="Theory anchor="operation" numbered="true" toc="default">
      <name>Theory of Operation" anchor='operation'> Operation</name>
      <t><xref target ='RFC9086'/> target="RFC9086" format="default"/> provides mechanisms to
      advertise the EPE-SIDs in BGP-LS. These EPE-SIDs may be used to build Segment Routing SR
      paths as and may be communicated using extensions described in <xref target ='I-D.ietf-idr-segment-routing-te-policy'/>
      target="I-D.ietf-idr-bgp-sr-segtypes-ext" format="default"/> and <xref
      target="I-D.ietf-idr-sr-policy-safi" format="default"/> or
using Path
      Computation Element Protocol (PCEP) extensions as defined in <xref target="RFC8664"/>.
      target="RFC8664" format="default"/>. Data plane monitoring for such
      paths which that consist of EPE-SIDs will use extensions defined in this
      document to build the Target FEC stack Stack TLV.  The MPLS Ping and
      Traceroute procedures
MAY <bcp14>MAY</bcp14> be initiated by the head-end of
      the Segment Routing SR path or a centralized topology-aware data plane monitoring system
      system, as described in <xref target="RFC8403"/>. target="RFC8403" format="default"/>.  The
      extensions in <xref target ='I-D.ietf-idr-segment-routing-te-policy'/> target="I-D.ietf-idr-bgp-sr-segtypes-ext"
      format="default"/>, <xref target="I-D.ietf-idr-sr-policy-safi"
      format="default"/>, and <xref target="RFC8664"/> target="RFC8664" format="default"/> do not
      define how to acquire and carry the details of the SID that can be used
      to construct the FEC.  Such extensions are out of the scope for this
      document.  The node initiating the data plane monitoring may acquire the
      details of EPE-SIDs through BGP-LS advertisements advertisements, as described in <xref target ='RFC9086'/>.
      target="RFC9086" format="default"/>.  There may be other possible
      mechanisms that can be used to learn the definition of the SID from the
      controller.  Details of such mechanisms are out of scope for this
      document.</t>
      <t>The EPE-SIDs are advertised for inter-AS links which that run EBGP
      sessions. <xref target ='RFC9086'/> target="RFC9086" format="default"/> does not define the
      detailed procedures of how to operate EBGP sessions in a scenario with
      unnumbered interfaces. Therefore, these scenarios are out of scope for
      this document.  Anycast and multicast addresses are not in the scope of
      this document. During the AS migration scenario scenario, procedures described in
      <xref target="RFC7705"/> target="RFC7705" format="default"/> may be in force.  In these
      scenarios, if the local and remote AS fields in the FEC
as (as described in
      <xref target="FEC_definitions"/> carries target="FEC_definitions" format="default"/>) carry the globally
      configured ASN AS Number and not the "local AS" as (as defined in <xref target="RFC7705"/>,
      target="RFC7705" format="default"/>), then the FEC validation procedures may
      fail. </t>
<t> As
      <t>As described in <xref target="intro"/>, target="intro" format="default"/>, this
      document defines Target FEC stack Stack TLVs for EPE-SIDs, EPE-SIDs that can be used in
      detecting MPLS data plane failures <xref target="RFC8029"/>. target="RFC8029"
      format="default"/>. This mechanism applies to paths created across
across
      ASes of co-operating cooperating administrations. If the ping or traceroute
      packet enters a non co-operating non-cooperating AS domain, it might be dropped by the
      routers in the
non co-operating non-cooperating domain. Although a complete path
      validation cannot be done across,
non co-operating across non-cooperating domains, it still
      provides useful information that the
 ping/traceroute ping or traceroute packet entered a non co-operating
      non-cooperating domain.</t>
    </section>
    <section title="Requirements Language"> numbered="true" toc="default">
      <name>Requirements Language</name>
      <t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
      "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
      NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>",
      "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
      "<bcp14>MAY</bcp14>", and
   "OPTIONAL" "<bcp14>OPTIONAL</bcp14>" in this document are
      to be interpreted as described in BCP 14, <xref target="RFC2119"/>, target="RFC2119"
      format="default"/>, <xref target="RFC8174"/> target="RFC8174" format="default"/> when, and
      only when, they appear in all capitals, as shown here. </t>
    </section>
    <section anchor='FEC_definitions' title='FEC Definitions'> anchor="FEC_definitions" numbered="true" toc="default">
      <name>FEC Definitions</name>
      <t>
   Three In this document, 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).</t>
   <figure anchor="sub_tlv" title="New sub-TLV types">
    <artwork>
            Sub-Type    Sub-TLV Name
            --------  ---------------
             TBD1      PeerAdj SID Sub-TLV
             TBD2      PeerNode SID Sub-TLV
             TBD3      PeerSet SID Sub-TLV

    </artwork>
    </figure> 21); see <xref target="sub_tlv"/>.</t>

      <section anchor='peer_node_sid' title='PeerNode anchor="peer_node_sid" numbered="true" toc="default">
        <name>PeerNode SID Sub-TLV'> Sub-TLV</name>
        <figure anchor="peer_node_sid_tlv" title="PeerNode anchor="peer_node_sid_tlv">
          <name>PeerNode SID Sub-TLV">

      <artwork> Sub-TLV</name>
          <artwork name="" type="" align="left" alt=""><![CDATA[
 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 39                      |          Length               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              Local AS Number (4 octets)                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              Remote AS Number (4 octets)                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              Local BGP router Router ID (4 octets)                   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              Remote BGP Router ID (4 octets)                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      </artwork>
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
        </figure>
        <t>Type                     : 2 octets </t>
		 <t>                          Value:TBD2</t>
        <t>Length                   : 2 octets </t>
		<t>                           Value: 16
                                      </t>

        <t>Local

	<dl>
	  <dt>Type:</dt><dd>2 octets</dd>
	  <dt>Value:</dt><dd>39</dd>
	  <dt>Length:</dt><dd>2 octets</dd>
	  <dt>Value:</dt><dd>16</dd>
          <dt>Local AS Number : 4 octets</t>

			<t>The Number:</dt><dd>4 octets. The unsigned integer
          representing the AS number <xref target ='RFC6793'/> target="RFC6793" format="default"/>
          of the AS to which the PeerNode SID advertising node belongs. If
          Confederations <xref target ='RFC5065'/> target="RFC5065" format="default"/> are in use,
          and if the remote node is a member of a different Member-AS within
          the local Confederation, this is the Member-AS Number inside the
          Confederation and not the Confederation Identifier.</t>

        <t>Remote Identifier.</dd>
          <dt>Remote AS Number : 4 octets</t>

			<t>The Number:</dt><dd>4 octets. The unsigned integer
          representing the AS number <xref target ='RFC6793'/> target="RFC6793" format="default"/>
          of the AS of the remote node for which the PeerNode SID is
          advertised. If Confederations <xref target ='RFC5065'/> target="RFC5065"
          format="default"/> are in use, and if the remote node is a member of
          a different Member-AS within the local Confederation, this is the
          Member-AS Number inside the Confederation and not the Confederation Identifier.</t>

        <t>Local
          Identifier.</dd>
	  <dt>Local BGP Router ID : 4 octets </t>
            <t>unsigned ID:</dt><dd>4 octets.  The unsigned integer
	  representing the BGP Identifier of the PeerNode SID advertising node
	  as defined in <xref target ='RFC4271'/> target="RFC4271" format="default"/> and <xref target ='RFC6286'/>. </t>
        <t>Remote
	  target="RFC6286" format="default"/>. </dd>
          <dt>Remote BGP Router ID :  4 octets</t>
            <t>unsigned ID:</dt><dd>4 octets.  The unsigned integer
          representing the BGP Identifier of the remote node as defined in
          <xref target ='RFC4271'/> target="RFC4271" format="default"/> and <xref target ='RFC6286'/>. </t> target="RFC6286"
          format="default"/>. </dd>
	</dl>

        <t>When there is a multi-hop EBGP session between two ASBRs, a
        PeerNode SID is advertised for this session session, and traffic can be
    load balanced
        load-balanced across these interfaces.  An EPE controller that does
        performs bandwidth management for these links should be aware of the
        links on which the traffic will be load-balanced. As per <xref target ='RFC8029'/>,
        target="RFC8029" format="default"/>, the node advertising the EPE SIDs EPE-SIDs
        will send a Downstream Detailed Mapping (DDMAP) TLV (DDMAP TLV) specifying the
        details of nexthop
    interfaces, the OAM packet will be sent out. next-hop interfaces. Based on this information information, the
        controller MAY <bcp14>MAY</bcp14> choose to verify the actual forwarding
        state with the topology information that the controller has.  On the
        router, the validation procedures will include, include the received DDMAP validation
        validation, as specified in <xref target ='RFC8029'/> target="RFC8029" format="default"/>,
        to verify the control state and the forwarding state synchronization
        on the two routers. Any discrepancies between the controller's state
        and the forwarding state will not be detected by the procedures
        described in the this document.</t>
      </section>
      <section anchor='peer_adj_sid' title='PeerAdj anchor="peer_adj_sid" numbered="true" toc="default">
        <name>PeerAdj SID Sub-TLV'> Sub-TLV</name>
        <figure anchor="peer_adj_sid_tlv" title="PeerAdj anchor="peer_adj_sid_tlv">
          <name>PeerAdj SID Sub-TLV">

      <artwork> Sub-TLV</name>
          <artwork name="" type="" align="left" alt=""><![CDATA[
 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 38                      |          Length               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Adj-Type Adj type      |            RESERVED                           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              Local AS Number (4 octets)                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              Remote AS Number (4 octets)                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              Local BGP router Router ID (4 octets)                   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              Remote BGP Router ID (4 octets)                  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              Local Interface address Address (4/16 octets)            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              Remote Interface address Address (4/16 octets)           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      </artwork>
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
        </figure>
        <t>Type             : 2

	<dl>

        <dt>Type:</dt><dd>2 octets </t>
		<t>                   Value: TBD1</t>

        <t>Length           : 2 octets</t>
		<t>                   Value: variable </dd>
        <dt>Value:</dt><dd>38</dd>
        <dt>Length:</dt><dd>2 octets</dd>
        <dt>Value:</dt><dd>Variable based on the IPv4/IPv6 interface
        address. Length excludes the length of the Type and Length
                              fields.For fields. For
        IPv4 interface addresses addresses, the length will be 28 octets.  In the case of an
        IPv6 address address, the length will be 52 octets.</t>
		<t>Adj-Type         : 1 octet</t>
		<t>                   Value: Set octets.</dd>
        <dt>Adj type:</dt><dd>1 octet</dd>
        <dt>Value:</dt><dd>Set to 1 when the Adjacency Segment is IPv4 IPv4. Set to
        2 when the Adjacency Segment is IPv6</t>
		<t> RESERVED        : 3 IPv6.</dd>
        <dt>RESERVED:</dt><dd>3 octets. MUST <bcp14>MUST</bcp14> be zero when sending,
        sending and ignored on receiving.</t>
        <t>Local receiving.</dd>
        <dt>Local AS Number  : 4 octets</t>
        <t>The Number:</dt><dd>4 octets. The unsigned integer
        representing the AS number <xref target ='RFC6793'/> target="RFC6793" format="default"/>
        of the AS to which the PeerAdj SID advertising node belongs. If
        Confederations <xref target ='RFC5065'/> target="RFC5065" format="default"/> are in use,
        and if the remote node is a member of a different Member-AS within the
        local Confederation, this is the Member-AS Number inside the
        Confederation and not the Confederation Identifier.</t>
        <t>Remote Identifier.</dd>
        <dt>Remote AS Number : 4 octets</t>
            <t>The Number:</dt><dd>4 octets.  The unsigned integer
        representing the AS number<xref target ='RFC6793'/>  of the AS number <xref target="RFC6793" format="default"/> of
        the remote node node's AS for which the PeerAdj SID is advertised. If
        Confederations <xref target ='RFC5065'/> target="RFC5065" format="default"/> are in use,
        and if the remote node is a member of a different Member-AS within the
        local Confederation, this is the Member-AS Number inside the
        Confederation and not the Confederation Identifier.</t>
        <t>Local Identifier.</dd>
        <dt>Local BGP Router ID : 4 octets </t>
            <t> ID:</dt><dd>4 octets. The unsigned integer
        representing the BGP Identifier of the PeerAdj SID advertising node as
        defined in <xref target ='RFC4271'/> target="RFC4271" format="default"/> and <xref target ='RFC6286'/>. </t>
        <t>Remote
        target="RFC6286" format="default"/>.</dd>
        <dt>Remote BGP Router ID : 4 octets </t>
            <t> ID:</dt><dd>4 octets. The unsigned integer
        representing the BGP Identifier of the remote node as defined in <xref target ='RFC4271'/>
        target="RFC4271" format="default"/> and <xref target ='RFC6286'/>. </t>
        <t>Local target="RFC6286"
        format="default"/>.</dd>
        <dt>Local Interface Address :4 octets/16 octets</t>
            <t>In Address:</dt><dd>4 octets or 16 octets. In the case of
        PeerAdj SID, Local the local interface address corresponding to the PeerAdj SID
        should be specified in this field.  For IPv4,this IPv4, this field is 4 octets;
        for IPv6, this field is 16 octets. Link-local IPv6 addresses are not
        in the scope of this document.</t>

         <t>Remote document.</dd>
        <dt>Remote Interface Address :4 octets/16 octets</t>
            <t>In Address:</dt><dd>4 octets or 16 octets.  In the
        case of PeerAdj SID Remote SID, the remote interface address corresponding to the
        PeerAdj SID should be apecified specified in this field.  For IPv4, this field
        is 4 octets; for IPv6, this field is 16 octets. Link-local IPv6
        addresses are not in the scope of this document..</t> document.</dd>
	</dl>

        <t><xref target ='RFC9086'/> target="RFC9086" format="default"/> mandates sending a local
        interface ID and remote interface ID in the Link Descriptors link descriptors and
        allows a value of 0 in the remote descriptors.  It is useful to
        validate the incoming interface for an OAM packet and packet, but if the remote
        descriptor is 0 0, this validation is not possible.
        <xref target ='RFC9086'/> allows optional  Optional link
        descriptors of local and remote interface addresses are allowed as
        described in section 4.2.  This document RECOMMENDs sending <xref target="RFC9086" sectionFormat="of"
        section="4.2"/>. In this document, it is <bcp14>RECOMMENDED</bcp14>
        to send these optional descriptors and using use them to validate incoming interface.
        interfaces.  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 <bcp14>SHOULD</bcp14> skip the
        validation for the incoming interface if the address field contains
        0.</t>
      </section>
      <section anchor='peer_set_sid' title='PeerSet anchor="peer_set_sid" numbered="true" toc="default">
        <name>PeerSet SID Sub-TLV'> Sub-TLV</name>
        <figure anchor="peer_set_sid_tlv" title="PeerSet anchor="peer_set_sid_tlv">
          <name>PeerSet SID Sub-TLV">

      <artwork> Sub-TLV</name>
          <artwork name="" type="" align="left" alt=""><![CDATA[
 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 40                     |          Length               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              Local AS Number (4 octets)                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              Local BGP router Router ID (4 octets)                   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   No.of    No. of elements in set     |          Reserved             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              Remote AS Number (4 octets)                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|              Remote BGP Router ID (4 octets)                  |
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++

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

      </artwork>
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++]]></artwork>
        </figure>
      <t>Type                  : 2 octets </t>
	  <t>                        Value: TBD3</t>
      <t>Length                : 2 octets </t>
	  <t>                        Value: Expressed

	<dl>
        <dt>Type:</dt><dd>2 octets</dd>
        <dt>Value:</dt><dd>40</dd>
        <dt>Length:</dt><dd>2 octets</dd>
        <dt>Value:</dt><dd>Expressed in octets and is a variable based on the
        number of elements in the set.  The length field does not include the
        length of Type and Length fields.</t>

        <t>Local fields.</dd>
        <dt>Local AS Number :4 octets </t>
           <t>The Number:</dt><dd>4 octets.  The unsigned integer
        representing the AS number <xref target ='RFC6793'/> target="RFC6793" format="default"/>
        of the AS to which the PeerSet SID advertising node belongs. If
        Confederations <xref target ='RFC5065'/> target="RFC5065" format="default"/> are in use,
        and if the remote node is a member of a different Member-AS within the
        local Confederation, this is the Member-AS Number inside the
        Confederation and not the Confederation Identifier.</t>
		 <t>Local Identifier.</dd>
        <dt>Local BGP Router ID : 4 octets </t>
            <t> ID:</dt><dd>4 octets.  The unsigned integer
        representing the BGP Identifier of the PeerSet SID advertising node node, as
        defined in <xref target ='RFC4271'/> target="RFC4271" format="default"/> and <xref target ='RFC6286'/>. </t>
		<t>No.of
        target="RFC6286" format="default"/>. </dd>
        <dt>No. of elements in set: 2 octets</t>
		<t> set:</dt><dd>2 octets.  The number of remote
        ASes over which the set SID performs load balancing.</t>
		 <t> Reserved : 2 load-balancing.</dd>
        <dt>Reserved:</dt><dd>2 octets. MUST <bcp14>MUST</bcp14> be zero when sent
        and ignored when received.</t>

        <t>Remote received.</dd>
        <dt>Remote AS Number : 4 octets </t>
            <t>The Number:</dt><dd>4 octets.  The unsigned integer
        representing the AS number <xref target ='RFC6793'/> of the AS target="RFC6793" format="default"/>
        of the remote node node's AS for which the PeerSet SID is
        advertised. If Confederations <xref target ='RFC5065'/> target="RFC5065"
        format="default"/> are in use, and if the remote node is a member of a
        different Member-AS within the local Confederation, this is the
        Member-AS Number inside the Confederation and not the Confederation Identifier.</t>

        <t>Remote
        Identifier.</dd>
        <dt>Remote BGP Router ID : 4 octets  </t>
            <t>unsigned ID:</dt><dd>4 octets.  The unsigned integer
        representing the BGP Identifier of the remote node as defined in <xref target ='RFC4271'/>
        target="RFC4271" format="default"/> and <xref target ='RFC6286'/>. </t> target="RFC6286"
        format="default"/>. </dd>
	  </dl>
        <t>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 and PeerAdj SIDs MUST <bcp14>MUST</bcp14> be included in the
        FEC.</t>
      </section>
    </section>
    <section anchor="validation" title="EPE-SID numbered="true" toc="default">
      <name>EPE-SID FEC validation">
 <t>
When Validation</name>
      <t>When a remote ASBR of the EPE-SID advertisement receives the MPLS OAM
      packet with the top FEC being the EPE-SID, it MUST <bcp14>MUST</bcp14>
      perform validity checks on the content of the EPE-SID FEC sub-TLV.  The
      basic length check should be performed on the received FEC. FEC.</t>
      <figure anchor="length_check" title="Length Validation">

      <artwork> anchor="length_check">
        <name>Length Validation</name>
        <artwork name="" type="" align="left" alt=""><![CDATA[
 PeerAdj SID sub-TLV
 -----------
 if
 If Adj type = 1 1, Length should be 28 octets
 If Adj type =2 = 2, Length should be 52 octets

 PeerNode SID sub-TLV
 -------------
 Length = ( 20 (20 + No.of No. of IPv4 interface pairs * 8 +
          No.of
           No. of IPv6 interface pairs * 32 ) 32) octets

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

           </artwork> 32) octets]]></artwork>
      </figure>
 </t>
 <t>
 If

      <t>If a malformed FEC sub-TLV is received, then a return code of 1,
      "Malformed echo request received" received", as defined in <xref target="RFC8029"/>
 MUST target="RFC8029"
      format="default"/> <bcp14>MUST</bcp14> be sent.  The below section below is
      appended to the procedure given in Section 7.4
   point step 4a of <xref target="RFC8287"/>. target="RFC8287"
      sectionFormat="of" section="7.4"/>.
      </t>

<!--[rfced] Section 5.1.

d) Should "the remote AS field" or "one of the remote AS
fields" be used for consistency?

Original:
   -  Validate that the receiving node's BGP Local AS matches
      with the remote AS field in the received PeerNode SID
      FEC sub-TLV.

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

      <section anchor="fec_validation" title="EPE-SID numbered="true" toc="default">
        <name>EPE-SID FEC validiation">
   <t>

     <t> Validation Rules</name>
	<t>This is an example of Segment Routing IGP-Prefix, IGP-Adjacency SID
	SID, and EPE-SID  Validation :
	 Receiving node validations.  Note that the term used "receiving node" in
	this section implies corresponds to the node that receives the OAM message
	with the Target FEC stack Stack TLV.</t>
      <artwork>

        <artwork name="" type="" align="left" alt=""><![CDATA[
Else, if the Label-stack-depth is 0 and the Target FEC Stack sub-TLV
at FEC-stack-depth FEC stack-depth is TBD1 38 (PeerAdj SID sub-TLV), {

    Set the Best-return-code to 10, "Mapping for this FEC is not
    the given label at stack-depth <RSC>" [RFC8029].  Check if
    any below conditions fail:

           -  Validate that the receiving node's BGP Local AS matches
              with the remote AS field in the received PeerAdj SID
                  FEC
              sub-TLV.

           -  Validate that the receiving node's BGP Router-ID
              matches with the Remote Router ID field in the
              received PeerAdj SID FEC. sub-TLV.

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

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

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

    If all above validations have passed, set the return code to 3 3,
    "Replying router is an egress for the FEC at stack-depth" stack-depth <RSC>"
    [RFC8029].
    }

Else, if the Target FEC Stack sub-TLV at FEC-stack-depth FEC stack-depth is TBD2 39
     (PeerNode SID sub-TLV), {

    Set the Best-return-code to 10, "Mapping for this FEC is not
    the given label at stack-depth <RSC>" [RFC8029].  Check if any
    below conditions fail:

       -  Validate that the receiving node's BGP Local AS matches
          with the remote AS field in the received PeerNode SID
          FEC sub-TLV.

       -  Validate that the receiving node's BGP Router-ID matches
          with the Remote Router ID field in the received
          PeerNode SID FEC.

       -  Validate that there is a an EBGP session with a peer
          having a local AS number and BGP Router-ID as
          specified in the Local 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 3,
    "Replying router is an egress for the FEC at stack-depth". stack-depth <RSC>"
    [RFC8029].
    }
Else, if the Target FEC Stack sub-TLV at FEC-stack-depth FEC stack-depth is TBD3 40
     (PeerSet SID sub-TLV), {

    Set the Best-return-code to 10, "Mapping for this FEC is not
    the given label at stack-depth" stack-depth <RSC>" [RFC8029].  Check if any
    below conditions fail:

       -  Validate that the Receiving Node receiving node's BGP Local AS matches
          with one of the remote AS field fields in the received
          PeerSet SID FEC sub-TLV.

       -  Validate that the Receiving Node receiving node's BGP Router-ID matches
          with one of the Remote Router ID field fields in the
          received PeerSet SID FEC sub-TLV.

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

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

</t> stack-depth <RSC>"
    [RFC8029].
    }]]></artwork>
      </section>
    </section>
    <section anchor="IANA" title="IANA Considerations">
    <t>IANA numbered="true" toc="default">
      <name>IANA Considerations</name>

<!-- [rfced] We have included some specific questions about the IANA
text below. In addition to responding to those questions, please
review all of the IANA-related updates carefully and let us know
if any further updates are needed.

a) It appears that the "IANA Considerations" section references the
"Sub-TLVs for TLV Types 1, 16, and 21" registry in the "Multiprotocol
Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters"
registry group, but it does not include a citation for this registry
here or in the references section.

May we add the following citation as a normative or informative
reference as shown below?

Original:
   IANA is requested to allocate 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.

        <list>
        <t>PeerAdj SID Sub-TLV : TBD1</t>
        <t>PeerNode SID Sub-TLV: TBD2</t>
        <t>PeerSet SID Sub-TLV : TBD3</t>
        </list>
    The

Perhaps:
   IANA has allocated three lowest free values new Target FEC stack sub-TLVs in the
   "Sub-TLVs for TLV Types 1, 16, and 21" registry
   [IANA-MPLS-LSP-PING-Parameters] within the "TLVs" registry of the
   "Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs)
   Ping Parameters" registry group.

Reference:
   [IANA-MPLS-LSP-PING-Parameters]
       IANA, "Sub-TLVs for TLV Types 1, 16, and 21",
       <https://www.iana.org/assignments/mpls-lsp-ping-parameters>.

b) We have removed "Sub-TLV" from the Standard Tracks range entries in Tables 1 and 2 per
IANA's note. Please let us know if "Sub-TLV" should be
removed from any other instances in the running text for consistency.
We note the following variations:

  PeerAdj SID
  PeerAdj SID FEC
  PeerAdj SID FEC sub-TLV
  PeerAdj SID Sub-TLV
  PeerAdj SID sub-TLV

  PeerSet SID sub-TLV
  PeerNode SID sub-TLV
-->

      <t>IANA has allocated if possible. three new Target FEC Stack sub-TLVs
    in the "Sub-TLVs for TLV Types 1, 16, and 21" registry <xref target="IANA-MPLS-LSP-PING-Parameters" format="default"/>
    within the "TLVs" registry of the "Multiprotocol Label Switching (MPLS)
    Label Switched Paths (LSPs) Ping Parameters" registry group. </t>

    <table anchor="sub_tlv" align="center">
      <name>Sub-TLVs for TLV Types 1, 16, and 21 Registry</name>
	<thead>
	  <tr>
	    <th>Sub-Type</th>
	    <th>Sub-TLV Name</th>
	  </tr>
	</thead>
	<tbody>
	  <tr>
	    <td>38</td>
            <td>PeerAdj SID</td>
	  </tr>
	  <tr>
	    <td>39</td>
	    <td>PeerNode SID</td>
	  </tr>
	  <tr>
	    <td>40</td>
            <td>PeerSet SID</td>
	  </tr>
	</tbody>
      </table>
    </section>
    <section title='Security Considerations' anchor='sec-con'> anchor="sec-con" numbered="true" toc="default">
      <name>Security Considerations</name>
      <t>The EPE-SIDs are advertised for egress links for Egress Peer Engineering EPE
       purposes or for inter-AS links between co-operating cooperating ASes.
       When co-operating cooperating domains are involved, they can allow the packets
       arriving on trusted interfaces to reach the control plane
       and get be processed.</t>
      <t> When EPE-SIDs are created for egress
       TE links where the neighbor AS is an independent entity, it may
       not allow the packets arriving from the external world to reach the
       control plane.  In such deployments deployments, the MPLS OAM packets will be
       dropped by the neighboring AS that receives the MPLS OAM packet.</t>
      <t>In MPLS traceroute Traceroute applications, when the AS boundary is
       crossed with the EPE-SIDs, the Target FEC stack Stack TLV is changed.
       <xref target="RFC8287"/> target="RFC8287" format="default"/> does not mandate that the initiator initiator,
       upon receiving an MPLS Echo Reply message that includes the
       Target FEC Stack Change TLV with one or more of the original
       segments being popped popped, remove a the corresponding FEC(s) from
       the Target FEC Stack TLV in the next (TTL+1) traceroute
       request. </t>
      <t>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.
       </t>

  </section>
  <section title='Implementation Status'>
  <t> This section is to be removed before publishing as an RFC.
  </t>
  <t>
  RFC-Editor: Please clean up
       the references cited by this section
   before publication.
  </t>
  <t>
  This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in
   <xref target ='RFC7942'/>.
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.
  </t>
  <section title='Juniper Networks'>

   <t>Juniper networks reported a prototype implementation of this draft.</t>

  </section>
  </section>
  <section title='Acknowledgments'>
    <t>Thanks to Loa Andersson, Dhruv Dhody, Ketan Talaulikar,
    Italo Busi and Alexander Vainshtein, Deepti Rathi  for
    careful review and comments. Thanks to Tarek Saad for providing the example
described in Appendix section. traceroute.
      </t>
    </section>

  </middle>
  <back>
  <references title='Normative References'>
    &RFC8287;
    &RFC8029;
    &RFC9086;
    &RFC2119;
    &RFC8174;
    &RFC8690;
	&RFC6793;
    <displayreference target="I-D.ietf-idr-bgp-sr-segtypes-ext" to="BGP-SR-SEGTYPES-EXT"/>
    <displayreference target="I-D.ietf-idr-sr-policy-safi" to="SR-BGP-POLICY"/>
    <references>
      <name>References</name>
      <references>
        <name>Normative References</name>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8287.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8029.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9086.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8690.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6793.xml"/>
      </references>
      <references>
        <name>Informative References</name>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9087.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7705.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8403.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8664.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4271.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5065.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6286.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9256.xml"/>

	<reference anchor="IANA-MPLS-LSP-PING-Parameters" target="https://www.iana.org/assignments/mpls-lsp-ping-parameters">
	<front>
	  <title>Sub-TLVs for TLV Types 1, 16, and 21</title>
	  <author>
	    <organization>IANA</organization>
	  </author>
	</front>
      </reference>

      <xi:include href="https://datatracker.ietf.org/doc/bibxml3/reference.I-D.ietf-idr-bgp-sr-segtypes-ext.xml"/>
      <xi:include href="https://datatracker.ietf.org/doc/bibxml3/reference.I-D.ietf-idr-sr-policy-safi.xml"/>

      </references>
  <references title='Informative References'>
    &RFC9087;
    &RFC7705;
    &RFC8403;
    &RFC8664;
    &RFC4271;
    &RFC5065;
    &RFC6286;
    &RFC7942;
    &RFC9256;
    <?rfc include="reference.I-D.ietf-idr-segment-routing-te-policy"?>
    </references>
    <section title='APPENDIX' anchor='APPENDIX'> anchor="Appendix" numbered="true" toc="default">
      <name>Examples of Programmed States</name>
      <t> This section describes an example examples of both a correctly programmed state and an
      incorrectly programmed state and provides details on how the new
      sub-TLVs described in this document can be used to validate the
      correctness.  Consider the diagram from <xref target ='reference_diagram'/>, target="reference_diagram"
      format="default"/>.</t>
      <t>Correctly programed programmed state:</t>
  <list>
<t>•	C

      <ul spacing="normal">
        <li>
          <t>C assigns label 16001 and binds it to adjacency C->E C-&gt;E </t>
<t>•	C
        </li>
        <li>
          <t>C signals that label 16001 is bound to adjacency C->E (e.g. C-&gt;E (e.g., via BGP-LS)</t>
<t>•	Controller/Ingress
        </li>
        <li>
          <t>The controller/ingress programs an SR path that has SID/label 16001
          to steer the packet on the exit point from C onto adjacency C->E</t>
<t>•	Using C-&gt;E</t>
        </li>
        <li>
          <t>Using MPLS trace Traceroute procedures defined in this document, the PeerAdj
          SID
Sub-TLV sub-TLV is populates populated with entities to be validated by C when the
          OAM packet reaches it.</t>
<t>•	C it</t>
        </li>
        <li>
          <t>C receives the OAM packet, it packet and validates that the top label
          (16001) is indeed corresponding to the entities populated in the
          PeerAdj SID Sub-TLV</t>
 </list> sub-TLV</t>
        </li>
      </ul>
      <t>Incorrectly programed programmed state:</t>
<list>
<t>•	C
      <ul spacing="normal">
        <li>
          <t>C assigns label 16001 and binds it to adjacency C->D</t>
<t>•	The C-&gt;D</t>
        </li>
        <li>
          <t>The controller learns of that PeerAdj SID label 16001 is bound to
          adjacency C->E (e.g. C-&gt;E (e.g., via BGP-LS) – -- this could be a software bug
          on C or on the controller</t>
<t>•	Controller/Ingress
        </li>
        <li>
          <t>The controller/ingress programs an SR path that has SID/label
          16001 to steer the packet on the exit point from C onto adjacency C->E</t>
<t>•	Using
          C-&gt;E</t>
        </li>
        <li>
          <t>Using MPLS trace Traceroute procedures defined in this document, the PeerAdj
          SID
Sub-TLV sub-TLV is populates populated with entities to be validated by C
          (including a local/remote interface address of C->E) C-&gt;E) when the OAM
          packet reaches it.</t>
<t>•	C it</t>
        </li>
        <li>
          <t>C receives the OAM packet, it packet and validates that the top label
          (16001) is NOT bound to C->E C-&gt;E as populated in the PeerAdj SID Sub-TLV
          sub-TLV and can respond then responds with the respective error code</t>
</list>
</t>
        </li>
      </ul>
    </section>
    <section numbered="false" toc="default">
      <name>Acknowledgments</name>

      <t>Thanks to <contact fullname="Loa Andersson"/>, <contact
      fullname="Dhruv Dhody"/>, <contact fullname="Ketan Talaulikar"/>,
      <contact fullname="Italo Busi"/>, <contact fullname="Alexander
      Vainshtein"/>, and <contact fullname="Deepti Rathi"/> for careful reviews and
      comments. Thanks to <contact fullname="Tarek Saad"/> for providing the
      example described in <xref target="Appendix"/>.</t>
    </section>

  </back>

<!-- [rfced] Terminology and Abbreviations

a) Throughout the text, the following terminology appears to be capitalized
inconsistently. Please review these occurrences and let us know if/how they
may be made consistent.

   Adj-Type vs. Adj type
   Integer vs. integer
   Local AS number vs. local AS number
   Local interface vs. local interface
   Link Descriptors vs. link descriptors
   Remote interface vs. remote interface

b) How may we make these terms consistent? For the case, we suggest
capitalizing "Target" and "Stack" to match use in RFC 8287 and
other past RFCs.

  Target FEC Stack TLV vs.
  Target FEC stack TLV vs.
  target FEC stack TLV vs.
  target FEC stack
     [Note: should the last instance contain "TLV"?]

  FEC stack TLV vs.
  FEC stack
     [Note: should "Target" be added to these instances? And
      should the last instance contain "TLV"?]

  Target FEC Stack sub-TLV vs.
  Target FEC stack sub-TLV vs.
  Target FEC sub-TLV
    [Note: should "Stack" be added to the last instance?]

c) In the text, "Type 1" appears to have two different names. Are these meant
to be the same or different? We see "Target FEC Stack TLV (Type 1)" in RFC 8287.
Please let us know how/if we may update. Note that we recommend making "stack"
uppercase for consistency.

Abstract:
   MPLS Target stack TLV (Type 1)

Section 4:
   Target FEC Stack TLV (Type 1)

d) It appears that in past RFCs, the term "FEC stack-depth" is used instead of
"FEC-stack-depth". Should we update to only one hyphen?

e) We see "MPLS Ping and Traceroute procedures" and "ping or traceroute packets"
in the running text. Should 1 instance of "MPLS traceroute procedure" perhaps be
"MPLS Ping and Traceroute procedures" for consistency?

Original:
   The data plane validation of the SID will be done during the
   MPLS traceroute procedure.

Perhaps:
   The data plane validation of the SID will be done during the
   MPLS Ping and Traceroute procedures.

f) FYI - We added expansions for the following abbreviations in the text.
Please review for accuracy.

   ASN: Access Service Network
   BGP-LS: Border Gateway Protocol - Link State
   EBGP: External BGP
   OAM: Operations, Administration, and Maintenance
-->

<!-- [rfced] Please review the "Inclusive Language" portion of the online
Style Guide <https://www.rfc-editor.org/styleguide/part2/#inclusive_language>
and let us know if any changes are needed.  Updates of this nature typically
result in more precise language, which is helpful for readers.

Note that our script did not flag any words in particular, but this should
still be reviewed as a best practice.
-->

</rfc>