<?xml version='1.0' encoding='utf-8'?>
<rfc xmlns:xi="http://www.w3.org/2001/XInclude" version="3" docName="draft-ietf-pce-binding-label-sid-16" number="9604" ipr="trust200902" obsoletes="" updates="" submissionType="IETF" category="std" consensus="true" xml:lang="en" tocInclude="true" tocDepth="4" symRefs="true" sortRefs="true" prepTime="2024-08-16T14:21:59" indexInclude="true" scripts="Common,Latin">
  <link href="https://datatracker.ietf.org/doc/draft-ietf-pce-binding-label-sid-16" rel="prev"/>
  <link href="https://dx.doi.org/10.17487/rfc9604" rel="alternate"/>
  <link href="urn:issn:2070-1721" rel="alternate"/>
  <front>
    <title abbrev="Binding Label/SID">Carrying Binding Label/SID in PCE-Based Networks</title>
    <seriesInfo name="RFC" value="9604" stream="IETF"/>
    <author fullname="Siva Sivabalan" initials="S." surname="Sivabalan">
      <organization showOnFrontPage="true">Ciena Corporation</organization>
      <address>
        <email>msiva282@gmail.com</email>
      </address>
    </author>
    <author fullname="Clarence Filsfils" initials="C." surname="Filsfils">
      <organization showOnFrontPage="true">Cisco Systems, Inc.</organization>
      <address>
        <postal>
          <extaddr>Pegasus Parc</extaddr>
          <street>De Kleetlaan 6a</street>
          <city>Brabant</city>
          <code>1831</code>
          <country>Belgium</country>
        </postal>
        <email>cfilsfil@cisco.com</email>
      </address>
    </author>
    <author fullname="Jeff Tantsura" initials="J." surname="Tantsura">
      <organization showOnFrontPage="true">Nvidia</organization>
      <address>
        <email>jefftant.ietf@gmail.com</email>
      </address>
    </author>
    <author fullname="Stefano Previdi" initials="S." surname="Previdi">
      <organization showOnFrontPage="true">Huawei Technologies</organization>
      <address>
        <email>stefano@previdi.net</email>
      </address>
    </author>
    <author fullname="Cheng Li" initials="C." role="editor">
      <organization showOnFrontPage="true">Huawei Technologies</organization>
      <address>
        <postal>
          <street>Huawei Campus, No. 156 Beiqing Rd.</street>
          <city>Beijing</city>
          <code>100095</code>
          <country>China</country>
        </postal>
        <email>c.l@huawei.com</email>
      </address>
    </author>
    <date month="08" year="2024"/>
    <area>rtg</area>
    <workgroup>pce</workgroup>
    <keyword>PCEP</keyword>
    <keyword>BSID</keyword>
    <keyword>Binding</keyword>
    <keyword>Binding Label</keyword>
    <abstract pn="section-abstract">
      <t indent="0" pn="section-abstract-1">In order to provide greater scalability, network confidentiality, and
      service independence, Segment Routing (SR) utilizes a Binding Segment Identifier (BSID),
      as described in RFC 8402. It is possible to associate a BSID to an
      RSVP-TE-signaled Traffic Engineering (TE) Label Switched Path (LSP) or
      an SR TE path. The BSID can be used by an upstream node for steering
      traffic into the appropriate TE path to enforce SR policies. This
      document specifies the concept of binding value, which can be either an
      MPLS label or a Segment Identifier (SID). It further specifies an extension to Path Computation
      Element Communication Protocol (PCEP) for reporting the binding value by
      a Path Computation Client (PCC) to the Path Computation Element (PCE) to
      support PCE-based TE policies.</t>
    </abstract>
    <boilerplate>
      <section anchor="status-of-memo" numbered="false" removeInRFC="false" toc="exclude" pn="section-boilerplate.1">
        <name slugifiedName="name-status-of-this-memo">Status of This Memo</name>
        <t indent="0" pn="section-boilerplate.1-1">
            This is an Internet Standards Track document.
        </t>
        <t indent="0" pn="section-boilerplate.1-2">
            This document is a product of the Internet Engineering Task Force
            (IETF).  It represents the consensus of the IETF community.  It has
            received public review and has been approved for publication by
            the Internet Engineering Steering Group (IESG).  Further
            information on Internet Standards is available in Section 2 of 
            RFC 7841.
        </t>
        <t indent="0" pn="section-boilerplate.1-3">
            Information about the current status of this document, any
            errata, and how to provide feedback on it may be obtained at
            <eref target="https://www.rfc-editor.org/info/rfc9604" brackets="none"/>.
        </t>
      </section>
      <section anchor="copyright" numbered="false" removeInRFC="false" toc="exclude" pn="section-boilerplate.2">
        <name slugifiedName="name-copyright-notice">Copyright Notice</name>
        <t indent="0" pn="section-boilerplate.2-1">
            Copyright (c) 2024 IETF Trust and the persons identified as the
            document authors. All rights reserved.
        </t>
        <t indent="0" pn="section-boilerplate.2-2">
            This document is subject to BCP 78 and the IETF Trust's Legal
            Provisions Relating to IETF Documents
            (<eref target="https://trustee.ietf.org/license-info" brackets="none"/>) 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 Revised BSD License text as described in
            Section 4.e of the Trust Legal Provisions and are provided without
            warranty as described in the Revised BSD License.
        </t>
      </section>
    </boilerplate>
    <toc>
      <section anchor="toc" numbered="false" removeInRFC="false" toc="exclude" pn="section-toc.1">
        <name slugifiedName="name-table-of-contents">Table of Contents</name>
        <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1">
          <li pn="section-toc.1-1.1">
            <t indent="0" keepWithNext="true" pn="section-toc.1-1.1.1"><xref derivedContent="1" format="counter" sectionFormat="of" target="section-1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-introduction">Introduction</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.1.2">
              <li pn="section-toc.1-1.1.2.1">
                <t indent="0" keepWithNext="true" pn="section-toc.1-1.1.2.1.1"><xref derivedContent="1.1" format="counter" sectionFormat="of" target="section-1.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-motivation-and-example">Motivation and Example</xref></t>
              </li>
              <li pn="section-toc.1-1.1.2.2">
                <t indent="0" keepWithNext="true" pn="section-toc.1-1.1.2.2.1"><xref derivedContent="1.2" format="counter" sectionFormat="of" target="section-1.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-summary-of-the-extension">Summary of the Extension</xref></t>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.2">
            <t indent="0" pn="section-toc.1-1.2.1"><xref derivedContent="2" format="counter" sectionFormat="of" target="section-2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-requirements-language">Requirements Language</xref></t>
          </li>
          <li pn="section-toc.1-1.3">
            <t indent="0" pn="section-toc.1-1.3.1"><xref derivedContent="3" format="counter" sectionFormat="of" target="section-3"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-terminology">Terminology</xref></t>
          </li>
          <li pn="section-toc.1-1.4">
            <t indent="0" pn="section-toc.1-1.4.1"><xref derivedContent="4" format="counter" sectionFormat="of" target="section-4"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-path-binding-tlv">Path Binding TLV</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.4.2">
              <li pn="section-toc.1-1.4.2.1">
                <t indent="0" pn="section-toc.1-1.4.2.1.1"><xref derivedContent="4.1" format="counter" sectionFormat="of" target="section-4.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-srv6-endpoint-behavior-and-">SRv6 Endpoint Behavior and SID Structure</xref></t>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.5">
            <t indent="0" pn="section-toc.1-1.5.1"><xref derivedContent="5" format="counter" sectionFormat="of" target="section-5"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-operation">Operation</xref></t>
          </li>
          <li pn="section-toc.1-1.6">
            <t indent="0" pn="section-toc.1-1.6.1"><xref derivedContent="6" format="counter" sectionFormat="of" target="section-6"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-binding-sid-in-sr-ero">Binding SID in SR-ERO</xref></t>
          </li>
          <li pn="section-toc.1-1.7">
            <t indent="0" pn="section-toc.1-1.7.1"><xref derivedContent="7" format="counter" sectionFormat="of" target="section-7"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-binding-sid-in-srv6-ero">Binding SID in SRv6-ERO</xref></t>
          </li>
          <li pn="section-toc.1-1.8">
            <t indent="0" pn="section-toc.1-1.8.1"><xref derivedContent="8" format="counter" sectionFormat="of" target="section-8"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-pce-allocation-of-binding-l">PCE Allocation of Binding Label/SID</xref></t>
          </li>
          <li pn="section-toc.1-1.9">
            <t indent="0" pn="section-toc.1-1.9.1"><xref derivedContent="9" format="counter" sectionFormat="of" target="section-9"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-security-considerations">Security Considerations</xref></t>
          </li>
          <li pn="section-toc.1-1.10">
            <t indent="0" pn="section-toc.1-1.10.1"><xref derivedContent="10" format="counter" sectionFormat="of" target="section-10"/>. <xref derivedContent="" format="title" sectionFormat="of" target="name-manageability-consideration">Manageability Considerations</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.10.2">
              <li pn="section-toc.1-1.10.2.1">
                <t indent="0" pn="section-toc.1-1.10.2.1.1"><xref derivedContent="10.1" format="counter" sectionFormat="of" target="section-10.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-control-of-function-and-pol">Control of Function and Policy</xref></t>
              </li>
              <li pn="section-toc.1-1.10.2.2">
                <t indent="0" pn="section-toc.1-1.10.2.2.1"><xref derivedContent="10.2" format="counter" sectionFormat="of" target="section-10.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-information-and-data-models">Information and Data Models</xref></t>
              </li>
              <li pn="section-toc.1-1.10.2.3">
                <t indent="0" pn="section-toc.1-1.10.2.3.1"><xref derivedContent="10.3" format="counter" sectionFormat="of" target="section-10.3"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-liveness-detection-and-moni">Liveness Detection and Monitoring</xref></t>
              </li>
              <li pn="section-toc.1-1.10.2.4">
                <t indent="0" pn="section-toc.1-1.10.2.4.1"><xref derivedContent="10.4" format="counter" sectionFormat="of" target="section-10.4"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-verify-correct-operations">Verify Correct Operations</xref></t>
              </li>
              <li pn="section-toc.1-1.10.2.5">
                <t indent="0" pn="section-toc.1-1.10.2.5.1"><xref derivedContent="10.5" format="counter" sectionFormat="of" target="section-10.5"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-requirements-on-other-proto">Requirements on Other Protocols</xref></t>
              </li>
              <li pn="section-toc.1-1.10.2.6">
                <t indent="0" pn="section-toc.1-1.10.2.6.1"><xref derivedContent="10.6" format="counter" sectionFormat="of" target="section-10.6"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-impact-on-network-operation">Impact on Network Operations</xref></t>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.11">
            <t indent="0" pn="section-toc.1-1.11.1"><xref derivedContent="11" format="counter" sectionFormat="of" target="section-11"/>. <xref derivedContent="" format="title" sectionFormat="of" target="name-iana-considerations">IANA Considerations</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.11.2">
              <li pn="section-toc.1-1.11.2.1">
                <t indent="0" pn="section-toc.1-1.11.2.1.1"><xref derivedContent="11.1" format="counter" sectionFormat="of" target="section-11.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-pcep-tlv-type-indicators">PCEP TLV Type Indicators</xref></t>
                <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.11.2.1.2">
                  <li pn="section-toc.1-1.11.2.1.2.1">
                    <t indent="0" pn="section-toc.1-1.11.2.1.2.1.1"><xref derivedContent="11.1.1" format="counter" sectionFormat="of" target="section-11.1.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-te-path-binding-tlv-2">TE-PATH-BINDING TLV</xref></t>
                  </li>
                </ul>
              </li>
              <li pn="section-toc.1-1.11.2.2">
                <t indent="0" pn="section-toc.1-1.11.2.2.1"><xref derivedContent="11.2" format="counter" sectionFormat="of" target="section-11.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-lsp-object">LSP Object</xref></t>
              </li>
              <li pn="section-toc.1-1.11.2.3">
                <t indent="0" pn="section-toc.1-1.11.2.3.1"><xref derivedContent="11.3" format="counter" sectionFormat="of" target="section-11.3"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-pcep-error-type-and-value">PCEP Error Type and Value</xref></t>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.12">
            <t indent="0" pn="section-toc.1-1.12.1"><xref derivedContent="12" format="counter" sectionFormat="of" target="section-12"/>. <xref derivedContent="" format="title" sectionFormat="of" target="name-references">References</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.12.2">
              <li pn="section-toc.1-1.12.2.1">
                <t indent="0" pn="section-toc.1-1.12.2.1.1"><xref derivedContent="12.1" format="counter" sectionFormat="of" target="section-12.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-normative-references">Normative References</xref></t>
              </li>
              <li pn="section-toc.1-1.12.2.2">
                <t indent="0" pn="section-toc.1-1.12.2.2.1"><xref derivedContent="12.2" format="counter" sectionFormat="of" target="section-12.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-informative-references">Informative References</xref></t>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.13">
            <t indent="0" pn="section-toc.1-1.13.1"><xref derivedContent="" format="none" sectionFormat="of" target="section-appendix.a"/><xref derivedContent="" format="title" sectionFormat="of" target="name-acknowledgements">Acknowledgements</xref></t>
          </li>
          <li pn="section-toc.1-1.14">
            <t indent="0" pn="section-toc.1-1.14.1"><xref derivedContent="" format="none" sectionFormat="of" target="section-appendix.b"/><xref derivedContent="" format="title" sectionFormat="of" target="name-contributors">Contributors</xref></t>
          </li>
          <li pn="section-toc.1-1.15">
            <t indent="0" pn="section-toc.1-1.15.1"><xref derivedContent="" format="none" sectionFormat="of" target="section-appendix.c"/><xref derivedContent="" format="title" sectionFormat="of" target="name-authors-addresses">Authors' Addresses</xref></t>
          </li>
        </ul>
      </section>
    </toc>
  </front>
  <middle>
    <section anchor="Introduction" numbered="true" toc="include" removeInRFC="false" pn="section-1">
      <name slugifiedName="name-introduction">Introduction</name>
      <t indent="0" pn="section-1-1">A Path Computation Element (PCE) can compute Traffic Engineering (TE)
      paths through a network where those paths are subject to
      various constraints. Currently, TE paths are set up using either the
      RSVP-TE signaling protocol or Segment Routing (SR). We refer to such
      paths as "RSVP-TE paths" and "SR-TE paths", respectively, in this
      document.</t>
      <t indent="0" pn="section-1-2">As per <xref target="RFC8402" format="default" sectionFormat="of" derivedContent="RFC8402"/>, SR allows a
      head-end node to steer a packet flow along a given path via an SR
      Policy.  As per <xref target="RFC9256" format="default" sectionFormat="of" derivedContent="RFC9256"/>, an SR Policy
      is a framework that enables the instantiation of an ordered list of
      segments on a node for implementing a source routing policy with a
      specific intent for traffic steering from that node.</t>
      <t indent="0" pn="section-1-3">As described in <xref target="RFC8402" format="default" sectionFormat="of" derivedContent="RFC8402"/>, a Binding
      SID (BSID) is bound to an SR Policy, instantiation of
      which may involve a list of Segment Identifiers (SIDs).  Any packets
      received with an active segment equal to a BSID are steered onto the
      bound SR Policy. A BSID may be either a local (SR Local Block (SRLB)) or
      a global (SR Global Block (SRGB)) SID. As per <xref target="RFC9256" sectionFormat="of" section="6.4" format="default" derivedLink="https://rfc-editor.org/rfc/rfc9256#section-6.4" derivedContent="RFC9256"/>, a BSID can also be associated with
      any type of interface or tunnel to enable the use of a non-SR interface
      or tunnel as a segment in a SID list. In this document, the term
      "binding label/SID" is used to generalize the allocation of a binding
      value for both SR and non-SR paths.</t>
      <t indent="0" pn="section-1-4"><xref target="RFC5440" format="default" sectionFormat="of" derivedContent="RFC5440"/> describes the PCEP for communication between
      a Path Computation Client (PCC) and a PCE or between a pair of PCEs as
      per <xref target="RFC4655" format="default" sectionFormat="of" derivedContent="RFC4655"/>. <xref target="RFC8231" format="default" sectionFormat="of" derivedContent="RFC8231"/> specifies
      extensions to PCEP that allow a PCC to delegate its Label Switched Paths
      (LSPs) to a stateful PCE. A stateful PCE can then update the state of
      LSPs delegated to it. <xref target="RFC8281" format="default" sectionFormat="of" derivedContent="RFC8281"/> specifies a mechanism
      allowing a PCE to dynamically instantiate an LSP on a PCC by sending the
      path and characteristics. This document specifies an extension to PCEP
      to manage the binding of label/SID that can be applied to SR, RSVP-TE,
      and other path setup types.</t>
      <t indent="0" pn="section-1-5"><xref target="RFC8664" format="default" sectionFormat="of" derivedContent="RFC8664"/> provides a mechanism for a PCE (acting as a
      network controller) to instantiate SR-TE paths (candidate paths) for an
      SR Policy onto a head-end node (acting as a PCC) using PCEP. For more
      information on the SR Policy Architecture, see <xref target="RFC9256" format="default" sectionFormat="of" derivedContent="RFC9256"/>.</t>
      <section anchor="Motivation" numbered="true" toc="include" removeInRFC="false" pn="section-1.1">
        <name slugifiedName="name-motivation-and-example">Motivation and Example</name>
        <t indent="0" pn="section-1.1-1">A binding label/SID has local significance to the ingress node of
        the corresponding TE path. When a stateful PCE is deployed for setting
        up TE paths, a binding label/SID reported from the PCC to the stateful
        PCE is useful for enforcing an end-to-end TE/SR policy. A
        sample Data Center (DC) and IP/MPLS WAN use case is illustrated in
        <xref target="figure1" format="default" sectionFormat="of" derivedContent="Figure 1"/> with a multi-domain PCE. In the IP/MPLS WAN,
        an SR-TE LSP is set up using the PCE. The list of SIDs of the SR-TE
        LSP is {A, B, C, D}. The gateway Node-1 (which is the PCC) allocates a
        binding SID X and reports it to the PCE. In the MPLS DC network, an
        end-to-end SR-TE LSP is established. In order for the access node to
        steer the traffic towards Node-1 and over the SR-TE path in WAN, the
        PCE passes the SID stack {Y, X} where Y is the node SID of the gateway
        Node-1 to the access node and X is the BSID. In the absence of the
        BSID X, the PCE would need to pass the SID stack {Y, A, B, C, D} to
        the access node. This example also illustrates the additional benefit
        of using the binding label/SID to reduce the number of SIDs imposed by
        the access nodes with a limited forwarding capacity.</t>
        <figure anchor="figure1" align="left" suppress-title="false" pn="figure-1">
          <name slugifiedName="name-a-sample-use-case-of-bindin">A Sample Use Case of Binding SID</name>
          <artwork align="center" name="" type="" alt="" pn="section-1.1-2.1">
           SID stack
           {Y, X}              +--------------+
                               | Multi-domain |
    _ _ _ _ _ _ _ _ _ _ _ _ _ _|     PCE      |
   |                           +--------------+
   |                              ^
   |                              | Binding
   |           .-----.            | SID (X)     .-----.
   |          (       )           |            (       )
   V       .--(         )--.      |        .--(         )--.
+------+  (                 )  +-------+  (                 )  +-------+
|Access|_(  MPLS DC Network  )_|Gateway|_(    IP/MPLS WAN    )_|Gateway|
| Node | (  ==============&gt;  ) |Node-1 | ( ================&gt; ) |Node-2 |
+------+  (    SR-TE path   )  +-------+  (    SR-TE path   )  +-------+
           '--(         )--'    Node       '--(         )--'
               (       )        SID of         (       )
                '-----'         Node-1          '-----'
                                is Y            SIDs for SR-TE LSP:
                                                {A, B, C, D}
</artwork>
        </figure>
        <t indent="0" pn="section-1.1-3">Using the extension defined in this document, a PCC could report to
        the stateful PCE the binding label/SID it allocated via a Path
        Computation LSP State Report (PCRpt) message. It is also possible for
        a stateful PCE to request a PCC to allocate a specific binding
        label/SID by sending a Path Computation LSP Update Request (PCUpd)
        message. If the PCC can successfully allocate the specified binding
        value, it reports the binding value to the PCE. Otherwise, the PCC
        sends an error message to the PCE indicating the cause of the failure.
        A local policy or configuration at the PCC <bcp14>SHOULD</bcp14> dictate if the
        binding label/SID needs to be assigned.</t>
      </section>
      <section anchor="Summary" numbered="true" toc="include" removeInRFC="false" pn="section-1.2">
        <name slugifiedName="name-summary-of-the-extension">Summary of the Extension</name>
        <t indent="0" pn="section-1.2-1">To implement the needed changes to PCEP, this document
        introduces a new <bcp14>OPTIONAL</bcp14> TLV that allows a PCC to report the
        binding label/SID associated with a TE LSP or a PCE to request a PCC
        to allocate any or a specific binding label/SID value. This TLV is
        intended for TE LSPs established using RSVP-TE, SR-TE, or any other
        future method. In the case of SR-TE LSPs, the TLV can carry a binding
        label (for SR-TE paths with the MPLS data plane) or a binding IPv6 SID
        (e.g., IPv6 address for SR-TE paths with the IPv6 data plane). Throughout
        this document, the term "binding value" means either an MPLS label or
        a SID.</t>
        <t indent="0" pn="section-1.2-2">As another way to use the extension specified in this document, to
        support the PCE-based central controller <xref target="RFC8283" format="default" sectionFormat="of" derivedContent="RFC8283"/>
        operation where the PCE would take responsibility for managing some
        part of the MPLS label space for each of the routers that it controls,
        the PCE could directly make the binding label/SID allocation and
        inform the PCC. See <xref target="PCECC" format="default" sectionFormat="of" derivedContent="Section 8"/> for details.</t>
        <t indent="0" pn="section-1.2-3">In addition to specifying a new TLV, this document specifies how
        and when a PCC and PCE can use this TLV, how they can allocate a
        binding label/SID, and the associated error handling.</t>
      </section>
    </section>
    <section numbered="true" toc="include" removeInRFC="false" pn="section-2">
      <name slugifiedName="name-requirements-language">Requirements Language</name>
      <t indent="0" pn="section-2-1">
    The key words "<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 "<bcp14>OPTIONAL</bcp14>" in this document are to be
    interpreted as described in BCP 14 <xref target="RFC2119" format="default" sectionFormat="of" derivedContent="RFC2119"/> <xref target="RFC8174" format="default" sectionFormat="of" derivedContent="RFC8174"/> when, and only when, they appear in all capitals, as
    shown here.
      </t>
    </section>
    <section numbered="true" toc="include" removeInRFC="false" pn="section-3">
      <name slugifiedName="name-terminology">Terminology</name>
      <t indent="0" pn="section-3-1">The following terminologies are used in this document: </t>
      <dl newline="false" spacing="normal" indent="3" pn="section-3-2">
        <dt pn="section-3-2.1">BSID:</dt>
        <dd pn="section-3-2.2">Binding SID</dd>
        <dt pn="section-3-2.3">binding label/SID:</dt>
        <dd pn="section-3-2.4">a generic term used for the binding segment for both SR and non-SR
        paths</dd>
        <dt pn="section-3-2.5">binding value:</dt>
        <dd pn="section-3-2.6">a generic term used for the binding segment as it can be encoded
        in various formats (as per the Binding Type (BT))</dd>
        <dt pn="section-3-2.7">LSP:</dt>
        <dd pn="section-3-2.8">Label Switched Path</dd>
        <dt pn="section-3-2.9">PCC:</dt>
        <dd pn="section-3-2.10">Path Computation Client</dd>
        <dt pn="section-3-2.11">PCEP:</dt>
        <dd pn="section-3-2.12">Path Computation Element Communication Protocol</dd>
        <dt pn="section-3-2.13">RSVP-TE:</dt>
        <dd pn="section-3-2.14">Resource Reservation Protocol - Traffic Engineering </dd>
        <dt pn="section-3-2.15">SID:</dt>
        <dd pn="section-3-2.16">Segment Identifier</dd>
        <dt pn="section-3-2.17">SR:</dt>
        <dd pn="section-3-2.18">Segment Routing</dd>
      </dl>
    </section>
    <section anchor="TE-PATH-BINDING-TLV" numbered="true" toc="include" removeInRFC="false" pn="section-4">
      <name slugifiedName="name-path-binding-tlv">Path Binding TLV</name>
      <t indent="0" pn="section-4-1">The new optional TLV called "TE-PATH-BINDING TLV" (the format is
      shown in <xref target="BINDING-LABEL-TLV-FORMAT" format="default" sectionFormat="of" derivedContent="Figure 2"/>) is defined to carry
      the binding label/SID for a TE path. This TLV is associated with the LSP
      object specified in <xref target="RFC8231" format="default" sectionFormat="of" derivedContent="RFC8231"/>. This TLV can also be
      carried in the PCEP-ERROR object <xref target="RFC5440" format="default" sectionFormat="of" derivedContent="RFC5440"/> in case of
      error. Multiple instances of TE-PATH-BINDING TLVs <bcp14>MAY</bcp14> be present in the
      LSP and PCEP-ERROR object. The type of this TLV is 55. The length is variable.</t>
      <figure anchor="BINDING-LABEL-TLV-FORMAT" align="left" suppress-title="false" pn="figure-2">
        <name slugifiedName="name-te-path-binding-tlv">TE-PATH-BINDING TLV</name>
        <artwork align="center" name="" type="" alt="" pn="section-4-2.1">
 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 = 55           |             Length            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      BT       |    Flags      |            Reserved           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~            Binding Value (variable length)                    ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
      </figure>
      <t indent="0" pn="section-4-3">The TE-PATH-BINDING TLV is a generic TLV such that it is able to carry
      binding label/SID (i.e., MPLS label or SRv6 SID). It is formatted
      according to the rules specified in <xref target="RFC5440" format="default" sectionFormat="of" derivedContent="RFC5440"/>. The value
      portion of the TLV comprises:</t>
      <ul bare="false" empty="false" indent="3" spacing="normal" pn="section-4-4">
        <li pn="section-4-4.1">
          <t indent="0" pn="section-4-4.1.1">Binding Type (BT): A one-octet field that identifies the type of
      binding included in the TLV. This document specifies the following BT
      values:</t>
          <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-4-4.1.2">
            <li pn="section-4-4.1.2.1">BT = 0: The binding value is a 20-bit MPLS label value. The TLV is
        padded to 4-bytes alignment. The Length <bcp14>MUST</bcp14> be set to
        7 (the padding is not included in the length, as per <xref target="RFC5440" sectionFormat="comma" section="7.1" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5440#section-7.1" derivedContent="RFC5440"/>), and the first
        20 bits are used to encode the MPLS label value.</li>
            <li pn="section-4-4.1.2.2">BT = 1: The binding value is a 32-bit MPLS Label Stack Entry as
        per <xref target="RFC3032" format="default" sectionFormat="of" derivedContent="RFC3032"/> with Label, Traffic
        Class (TC) <xref target="RFC5462" format="default" sectionFormat="of" derivedContent="RFC5462"/>, S, and TTL
        values encoded. Note that the receiver <bcp14>MAY</bcp14> choose to
        override TC, S, and TTL values according to its local policy. The
        Length <bcp14>MUST</bcp14> be set to 8.</li>
            <li pn="section-4-4.1.2.3">BT = 2: The binding value is an SRv6 SID with the format of a
        16-octet IPv6 address, representing the binding SID for SRv6. The
        Length <bcp14>MUST</bcp14> be set to 20.</li>
            <li pn="section-4-4.1.2.4">BT = 3: The binding value is a 24-octet field, defined in <xref target="Behavior-Structure" format="default" sectionFormat="of" derivedContent="Section 4.1"/>, that contains the SRv6
        SID as well as its Behavior and Structure. The Length
        <bcp14>MUST</bcp14> be set to 28.</li>
          </ul>
          <t indent="0" pn="section-4-4.1.3"><xref target="IANA-TLV" format="default" sectionFormat="of" derivedContent="Section 11.1.1"/> defines the IANA registry used to maintain
      these binding types as well as any future ones. Note that multiple
      TE-PATH-BINDING TLVs with the same or different binding types <bcp14>MAY</bcp14> be present
      for the same LSP. A PCEP speaker could allocate multiple TE-PATH-BINDING
      TLVs (of the same BT) and use different binding values in different
      domains or use cases based on a local policy.</t>
        </li>
        <li pn="section-4-4.2">
          <t indent="0" pn="section-4-4.2.1">Flags: 1 octet of flags. The following flag is defined in the new
      "TE-PATH-BINDING TLV Flag field" registry as described in <xref target="IANA-TLV" format="default" sectionFormat="of" derivedContent="Section 11.1.1"/>:</t>
          <figure anchor="BINDING-LABEL-FLAGS" align="left" suppress-title="false" pn="figure-3">
            <name slugifiedName="name-flags">Flags</name>
            <artwork align="left" name="" type="" alt="" pn="section-4-4.2.2.1">
 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|R|             |
+-+-+-+-+-+-+-+-+
</artwork>
          </figure>
          <t indent="0" pn="section-4-4.2.3">Where: </t>
          <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-4-4.2.4">
            <li pn="section-4-4.2.4.1">R (Removal - 1 bit): When set, the requesting PCEP peer requires
        the removal of the binding value for the LSP. When unset, the PCEP
        peer indicates that the binding value is added or retained for the
        LSP. This flag is used in the PCRpt and PCUpd messages. It is ignored
        in other PCEP messages.</li>
            <li pn="section-4-4.2.4.2">The unassigned flags <bcp14>MUST</bcp14> be set to 0 while sending
        and ignored on receipt.</li>
          </ul>
        </li>
        <li pn="section-4-4.3">
          <t indent="0" pn="section-4-4.3.1">Reserved: <bcp14>MUST</bcp14> be set to 0 while sending and ignored on receipt.</t>
        </li>
        <li pn="section-4-4.4">
          <t indent="0" pn="section-4-4.4.1">Binding Value: A variable-length field, padded with trailing zeros to
      a 4-octet boundary. When the BT is 0, the 20 bits represent the MPLS
      label. When the BT is 1, the 32 bits represent the MPLS label stack
      entry as per <xref target="RFC3032" format="default" sectionFormat="of" derivedContent="RFC3032"/>. When the BT is 2, the 128 bits
      represent the SRv6 SID. When the BT is 3, the binding value also
      contains the SRv6 Endpoint Behavior and SID Structure, defined in <xref target="Behavior-Structure" format="default" sectionFormat="of" derivedContent="Section 4.1"/>. In this document, the TE-PATH-BINDING TLV
      is considered to be empty if no binding value is present. Note that the
      length of the TLV would be 4 in such a case.</t>
        </li>
      </ul>
      <section anchor="Behavior-Structure" numbered="true" toc="include" removeInRFC="false" pn="section-4.1">
        <name slugifiedName="name-srv6-endpoint-behavior-and-">SRv6 Endpoint Behavior and SID Structure</name>
        <t indent="0" pn="section-4.1-1">This section specifies the format of the binding value in the
        TE-PATH-BINDING TLV when the BT is set to 3 for the SRv6 Binding SIDs
        <xref target="RFC8986" format="default" sectionFormat="of" derivedContent="RFC8986"/>. The format is shown in <xref target="SID-BEHAVIOR-AND-STRUCTURE" format="default" sectionFormat="of" derivedContent="Figure 4"/>.</t>
        <figure anchor="SID-BEHAVIOR-AND-STRUCTURE" align="left" suppress-title="false" pn="figure-4">
          <name slugifiedName="name-srv6-endpoint-behavior-and-s">SRv6 Endpoint Behavior and SID Structure</name>
          <artwork align="center" name="" type="" alt="" pn="section-4.1-2.1">
 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|                 SRv6 Binding SID (16 octets)                  |
|                                                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|         Reserved              |      Endpoint Behavior        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    LB Length  |    LN Length  | Fun. Length   |  Arg. Length  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
        </figure>
        <t indent="0" pn="section-4.1-3">The Binding Value consists of:</t>
        <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-4.1-4">
          <li pn="section-4.1-4.1">SRv6 Binding SID: 16 octets. The 128-bit IPv6 address,
          representing the binding SID for SRv6.</li>
          <li pn="section-4.1-4.2">Reserved: 2 octets. It <bcp14>MUST</bcp14> be set to 0 on
          transmit and ignored on receipt.</li>
          <li pn="section-4.1-4.3">Endpoint Behavior: 2 octets. The Endpoint Behavior code point
          for this SRv6 SID as defined by the "SRv6 Endpoint
          Behaviors" registry <xref target="RFC8986" format="default" sectionFormat="of" derivedContent="RFC8986"/>. When the field is set with the value 0, the
          Endpoint Behavior is considered unknown.</li>
          <li pn="section-4.1-4.4">
            <t indent="0" pn="section-4.1-4.4.1"><xref target="RFC8986" format="default" sectionFormat="of" derivedContent="RFC8986"/> defines an SRv6 SID
            as consisting of LOC:FUNCT:ARG, where a locator (LOC) is encoded
            in the L most significant bits of the SID, followed by F bits of
            function (FUNCT) and A bits of arguments (ARG). A locator may be
            represented as B:N, where B is the SRv6 SID locator block (IPv6
            prefix allocated for SRv6 SIDs by the operator) and N is the
            identifier of the parent node instantiating the SID, called "locator
            node". The following fields are used to advertise the length of
            each individual part of the SRv6 SID:</t>
            <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-4.1-4.4.2">
              <li pn="section-4.1-4.4.2.1">LB Length: 1 octet. SRv6 SID Locator Block length in
              bits.</li>
              <li pn="section-4.1-4.4.2.2">LN Length: 1 octet. SRv6 SID Locator Node length in
              bits.</li>
              <li pn="section-4.1-4.4.2.3">Function Length: 1 octet. SRv6 SID Function length in
              bits.</li>
              <li pn="section-4.1-4.4.2.4">Arguments Length: 1 octet. SRv6 SID Arguments length in
              bits.</li>
            </ul>
          </li>
        </ul>
        <t indent="0" pn="section-4.1-5">The total of the locator block, locator node, function, and
        arguments lengths <bcp14>MUST</bcp14> be less than or equal to 128 bits. If this condition
        is not met, the corresponding TE-PATH-BINDING TLV is considered
        invalid. Also, if the Endpoint Behavior is found to be unknown or
        inconsistent, it is considered invalid. A PCErr message with
        Error-Type = 10 ("Reception of an invalid object") and Error-value =
        37 ("Invalid SRv6 SID Structure") <bcp14>MUST</bcp14> be sent in such cases.</t>
        <t indent="0" pn="section-4.1-6">The SRv6 SID Structure could be used by the PCE for ease of
        operations and monitoring. For example, this information could be used
        for validation of SRv6 SIDs being instantiated in the network and
        checked for conformance to the SRv6 SID allocation scheme chosen by
        the operator as described in <xref target="RFC8986" sectionFormat="of" section="3.2" format="default" derivedLink="https://rfc-editor.org/rfc/rfc8986#section-3.2" derivedContent="RFC8986"/>.
        In the future, PCE could also be used for verification and for
        automatically securing the SRv6 domain by provisioning filtering
        rules at SR domain boundaries as described in <xref target="RFC8754" sectionFormat="of" section="5" format="default" derivedLink="https://rfc-editor.org/rfc/rfc8754#section-5" derivedContent="RFC8754"/>. The details of these potential applications are
        outside the scope of this document.</t>
      </section>
    </section>
    <section anchor="Operation" numbered="true" toc="include" removeInRFC="false" pn="section-5">
      <name slugifiedName="name-operation">Operation</name>
      <t indent="0" pn="section-5-1">The binding value is usually allocated by the PCC and reported to a
      PCE via a PCRpt message (see <xref target="PCECC" format="default" sectionFormat="of" derivedContent="Section 8"/> where PCE performs the
      allocation). If a PCE does not recognize the TE-PATH-BINDING TLV, it
      would ignore the TLV in accordance with <xref target="RFC5440" format="default" sectionFormat="of" derivedContent="RFC5440"/>. If a
      PCE recognizes the TLV but does not support the TLV, it <bcp14>MUST</bcp14> send a
      PCErr with Error-Type = 2 ("Capability not supported").</t>
      <t indent="0" pn="section-5-2">Multiple TE-PATH-BINDING TLVs are allowed to be present in the same
      LSP object. This signifies the presence of multiple binding SIDs for the
      given LSP. In the case of multiple TE-PATH-BINDING TLVs, the existing
      instances of TE-PATH-BINDING TLVs <bcp14>MAY</bcp14> be included in the LSP object. In
      case of an error condition, the whole message is rejected, and the
      resulting PCErr message <bcp14>MAY</bcp14> include the offending TE-PATH-BINDING TLV in
      the PCEP-ERROR object.</t>
      <t indent="0" pn="section-5-3">If a PCE recognizes an invalid binding value (e.g., label value from
      the reserved MPLS label space), it <bcp14>MUST</bcp14> send a PCErr message with
      Error-Type = 10 ("Reception of an invalid object") and Error-value = 2
      ("Bad label value") as specified in <xref target="RFC8664" format="default" sectionFormat="of" derivedContent="RFC8664"/>.</t>
      <t indent="0" pn="section-5-4">For SRv6 BSIDs, it is <bcp14>RECOMMENDED</bcp14> to always explicitly specify the
      SRv6 Endpoint Behavior and SID Structure in the TE-PATH-BINDING TLV by
      setting BT to 3. This can enable the sender to have
      control of the SRv6 Endpoint Behavior and SID Structure. A sender <bcp14>MAY</bcp14>
      choose to set the BT to 2, in which case the receiving implementation
      chooses how to interpret the SRv6 Endpoint Behavior and SID Structure
      according to local policy.</t>
      <t indent="0" pn="section-5-5">If a PCC wishes to withdraw a previously reported binding value, it
      <bcp14>MUST</bcp14> send a PCRpt message with the specific TE-PATH-BINDING TLV with R
      flag set to 1. If a PCC wishes to modify a previously reported binding,
      it <bcp14>MUST</bcp14> withdraw the former binding value (with R flag set in the former
      TE-PATH-BINDING TLV) and include a new TE-PATH-BINDING TLV containing
      the new binding value. Note that other instances of TE-PATH-BINDING TLVs
      that are unchanged <bcp14>MAY</bcp14> also be included. If the unchanged instances are
      not included, they will remain associated with the LSP.</t>
      <t indent="0" pn="section-5-6">If a PCE requires a PCC to allocate one (or several) specific binding
      value(s), it may do so by sending a PCUpd or PCInitiate message
      containing one or more TE-PATH-BINDING TLVs. If the values can be successfully
      allocated, the PCC reports the binding values to the PCE. If the PCC
      considers the binding value specified by the PCE invalid, it <bcp14>MUST</bcp14> send a
      PCErr message with Error-Type = 32 ("Binding label/SID failure") and
      Error-value = 1 ("Invalid SID"). If the binding value is valid but
      the PCC is unable to allocate the binding value, it <bcp14>MUST</bcp14> send a PCErr
      message with Error-Type = 32 ("Binding label/SID failure") and Error-value = 2 ("Unable to allocate the specified binding value"). Note
      that, in case of an error, the PCC rejects the PCUpd or PCInitiate
      message in its entirety and can include the offending TE-PATH-BINDING
      TLV in the PCEP-ERROR object.</t>
      <t indent="0" pn="section-5-7">If a PCE wishes to request the withdrawal of a previously reported
      binding value, it <bcp14>MUST</bcp14> send a PCUpd message with the specific
      TE-PATH-BINDING TLV with R flag set to 1. If a PCE wishes to modify a
      previously requested binding value, it <bcp14>MUST</bcp14> request the withdrawal of
      the former binding value (with R flag set in the former TE-PATH-BINDING
      TLV) and include a new TE-PATH-BINDING TLV containing the new binding
      value. If a PCC receives a PCUpd message with TE-PATH-BINDING TLV where
      the R flag is set to 1, but either the binding value is missing (empty
      TE-PATH-BINDING TLV) or the binding value is incorrect, it <bcp14>MUST</bcp14> send a
      PCErr message with Error-Type = 32 ("Binding label/SID failure") and
      Error-value = 4 ("Unable to remove the binding value").</t>
      <t indent="0" pn="section-5-8">In some cases, a stateful PCE may want to request that the PCC
      allocate a binding value of the PCC's own choosing. It instructs the PCC
      by sending a PCUpd message containing an empty TE-PATH-BINDING TLV,
      i.e., no binding value is specified (bringing the Length field of the
      TLV to 4). A PCE can also request that a PCC allocate a binding value at
      the time of initiation by sending a PCInitiate message with an empty
      TE-PATH-BINDING TLV.  Only one such instance of empty TE-PATH-BINDING
      TLV, per BT, <bcp14>SHOULD</bcp14> be included in the LSP object; others
      should be ignored on receipt.  If the PCC is unable to allocate a new
      binding value as per the specified BT, it <bcp14>MUST</bcp14> send a
      PCErr message with Error-Type = 32 ("Binding label/SID failure") and
      Error-value = 3 ("Unable to allocate a new binding label/SID").</t>
      <t indent="0" pn="section-5-9">As previously noted, if a message contains an invalid TE-PATH-BINDING
      TLV that leads to an error condition, the whole message is rejected
      including any other valid instances of TE-PATH-BINDING TLVs, if any. The
      resulting error message <bcp14>MAY</bcp14> include the offending TE-PATH-BINDING TLV in
      the PCEP-ERROR object.</t>
      <t indent="0" pn="section-5-10">If a PCC receives a TE-PATH-BINDING TLV in any message other than
      PCUpd or PCInitiate, it <bcp14>MUST</bcp14> close the corresponding PCEP session with
      the reason "Reception of a malformed PCEP message" (according to <xref target="RFC5440" format="default" sectionFormat="of" derivedContent="RFC5440"/>). Similarly, if a PCE receives a TE-PATH-BINDING TLV
      in any message other than a PCRpt or if the TE-PATH-BINDING TLV is
      associated with any object other than an LSP or PCEP-ERROR object, the
      PCE <bcp14>MUST</bcp14> close the corresponding PCEP session with the reason "Reception
      of a malformed PCEP message" (according to <xref target="RFC5440" format="default" sectionFormat="of" derivedContent="RFC5440"/>).</t>
      <t indent="0" pn="section-5-11">If a TE-PATH-BINDING TLV is absent in the PCRpt message and no
      binding values were previously reported, the PCE <bcp14>MUST</bcp14> assume that the
      corresponding LSP does not have any binding. Similarly, if
      TE-PATH-BINDING TLV is absent in the PCUpd message and no binding values
      were previously reported, the PCC's local policy dictates how the binding
      allocations are made for a given LSP.</t>
      <t indent="0" pn="section-5-12">Note that some binding types have similar information but different
      binding value formats. For example, BT=(2 or 3) is used for the SRv6 SID,
      and BT=(0 or 1) is used for the MPLS Label. In case a PCEP speaker
      receives multiple TE-PATH-BINDING TLVs with the same SRv6 SID or MPLS
      Label but different BT values, it <bcp14>MUST</bcp14> send a PCErr message with
      Error-Type = 32 ("Binding label/SID failure") and Error-value = 5
      ("Inconsistent binding types").</t>
    </section>
    <section anchor="SR-ERO" numbered="true" toc="include" removeInRFC="false" pn="section-6">
      <name slugifiedName="name-binding-sid-in-sr-ero">Binding SID in SR-ERO</name>
      <t indent="0" pn="section-6-1">In PCEP messages, LSP route information is carried in the Explicit
      Route Object (ERO), which consists of a sequence of subobjects. <xref target="RFC8664" format="default" sectionFormat="of" derivedContent="RFC8664"/> defines the "SR-ERO subobject"
      capable of carrying a SID as well as the identity of the Node or
      Adjacency Identifier (NAI) represented by the SID. The NAI Type (NT)
      field indicates the type and format of the NAI contained in the
      SR-ERO. In case of binding SID, the NAI <bcp14>MUST NOT</bcp14> be
      included and NT <bcp14>MUST</bcp14> be set to zero. <xref target="RFC8664" sectionFormat="of" section="5.2.1" format="default" derivedLink="https://rfc-editor.org/rfc/rfc8664#section-5.2.1" derivedContent="RFC8664"/> specifies bit
      settings and error handling in the case when NT=0.
      </t>
    </section>
    <section anchor="SRv6-ERO" numbered="true" toc="include" removeInRFC="false" pn="section-7">
      <name slugifiedName="name-binding-sid-in-srv6-ero">Binding SID in SRv6-ERO</name>
      <t indent="0" pn="section-7-1"><xref target="RFC9603" format="default" sectionFormat="of" derivedContent="RFC9603"/> defines the "SRv6-ERO
      subobject" for an SRv6 SID. Similarly to SR-ERO (<xref target="SR-ERO" format="default" sectionFormat="of" derivedContent="Section 6"/>), the NAI <bcp14>MUST NOT</bcp14> be included and
      the NT <bcp14>MUST</bcp14> be set to zero. <xref target="RFC8664" sectionFormat="of" section="5.2.1" format="default" derivedLink="https://rfc-editor.org/rfc/rfc8664#section-5.2.1" derivedContent="RFC8664"/> specifies bit settings and error
      handling in the case when NT=0.</t>
    </section>
    <section anchor="PCECC" toc="include" numbered="true" removeInRFC="false" pn="section-8">
      <name slugifiedName="name-pce-allocation-of-binding-l">PCE Allocation of Binding Label/SID</name>
      <t indent="0" pn="section-8-1"><xref target="Operation" format="default" sectionFormat="of" derivedContent="Section 5"/> already includes the scenario where a PCE
      requires a PCC to allocate a specified binding value by sending a PCUpd
      or PCInitiate message containing a TE-PATH-BINDING TLV. This section
      specifies an <bcp14>OPTIONAL</bcp14> feature for the PCE to allocate the binding
      label/SID of its own accord in the case where the PCE also controls the
      label space of the PCC and can make the label allocation on its own as
      described in <xref target="RFC8283" format="default" sectionFormat="of" derivedContent="RFC8283"/>. Note that the act of requesting a
      specific binding value (<xref target="Operation" format="default" sectionFormat="of" derivedContent="Section 5"/>) is different from
      the act of allocating a binding label/SID as described in this
      section.</t>
      <t indent="0" pn="section-8-2"><xref target="RFC8283" format="default" sectionFormat="of" derivedContent="RFC8283"/> introduces the architecture for PCE as a
      central controller as an extension of the architecture described in
      <xref target="RFC4655" format="default" sectionFormat="of" derivedContent="RFC4655"/> and assumes the continued use of PCEP as the
      protocol used between PCE and PCC. <xref target="RFC9050" format="default" sectionFormat="of" derivedContent="RFC9050"/> specifies
      the procedures and PCEP extensions for using the PCE as the central
      controller. It assumes that the exclusive label range to be used by a
      PCE is known and set on both PCEP peers. A future extension could add
      the capability to advertise this range via a possible PCEP extension as
      well (see <xref target="I-D.ietf-pce-controlled-id-space" format="default" sectionFormat="of" derivedContent="PCE-ID-SPACE"/>).</t>
      <t indent="0" pn="section-8-3">When PCE as a Central Controller (PCECC) operations are supported as per <xref target="RFC9050" format="default" sectionFormat="of" derivedContent="RFC9050"/>,
      the binding label/SID <bcp14>MAY</bcp14> also be allocated by the PCE itself. Both
      peers need to exchange the PCECC capability as described in <xref target="RFC9050" format="default" sectionFormat="of" derivedContent="RFC9050"/> before the PCE can allocate the binding label/SID on
      its own.</t>
      <t indent="0" pn="section-8-4">A new P flag in the LSP object <xref target="RFC8231" format="default" sectionFormat="of" derivedContent="RFC8231"/> is introduced
      to indicate that the allocation needs to be made by the PCE. Note that
      the P flag could be used for other types of allocations (such as path
      segments <xref target="I-D.ietf-pce-sr-path-segment" format="default" sectionFormat="of" derivedContent="PCEP-SR"/>) in the future. </t>
      <t indent="3" pn="section-8-5">P (PCE-allocation): If the bit is set to 1, it indicates
        that the PCC requests that the PCE make allocations for this LSP. The
        TE-PATH-BINDING TLV in the LSP object identifies that the allocation
        is for a binding label/SID. A PCC <bcp14>MUST</bcp14> set this bit to
        1 and include a TE-PATH-BINDING TLV in the LSP object if it wishes to
        request an allocation for a binding label/SID by the PCE in the PCEP
        message. A PCE <bcp14>MUST</bcp14> also set this bit to 1 and include
        a TE-PATH-BINDING TLV to indicate that the binding label/SID is
        allocated by PCE and encoded in the PCEP message towards the
        PCC. Further, if the binding label/SID is allocated by the PCC, the
        PCE <bcp14>MUST</bcp14> set this bit to 0 and follow the procedure
        described in <xref target="Operation" format="default" sectionFormat="of" derivedContent="Section 5"/>.</t>
      <t indent="0" pn="section-8-6">Note that: </t>
      <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-8-7">
        <li pn="section-8-7.1">A PCE could allocate the binding label/SID of its own accord for
          a PCE-initiated or PCE-delegated LSP and inform the PCC in the
          PCInitiate message or PCUpd message by setting P=1 and including
          TE-PATH-BINDING TLV in the LSP object.</li>
        <li pn="section-8-7.2">To let the PCC allocate the binding label/SID, a PCE <bcp14>MUST</bcp14> set P=0
          and include an empty TE-PATH-BINDING TLV (i.e., no binding value is
          specified) in the LSP object in the PCInitiate/PCUpd message.</li>
        <li pn="section-8-7.3">To request that the PCE allocate the binding label/SID, a PCC
        <bcp14>MUST</bcp14> set P=1, D=1, and include an empty TE-PATH-BINDING
        TLV in the PCRpt message.  The PCE will attempt to allocate it and
        respond to the PCC with a PCUpd message that includes the allocated
        binding label/SID in the TE-PATH-BINDING TLV and P=1 and D=1 in the
        LSP object. If the PCE is unable to allocate the binding label/SID, it
        <bcp14>MUST</bcp14> send a PCErr message with Error-Type = 32
        ("Binding label/SID failure") and Error-value = 3 ("Unable to allocate
        a new binding label/SID").</li>
        <li pn="section-8-7.4">
          <t indent="0" pn="section-8-7.4.1">If one or both speakers (PCE and PCC) have not indicated support
          and willingness to use the PCEP extensions for the PCECC as per
          <xref target="RFC9050" format="default" sectionFormat="of" derivedContent="RFC9050"/> and a PCEP peer receives P=1 in the LSP
          object, they <bcp14>MUST</bcp14>: </t>
          <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-8-7.4.2">
            <li pn="section-8-7.4.2.1">send a PCErr message with Error-Type = 19 ("Invalid Operation")
              and Error-value = 16 ("Attempted PCECC operations when PCECC
              capability was not advertised") and</li>
            <li pn="section-8-7.4.2.2">terminate the PCEP session.</li>
          </ul>
        </li>
        <li pn="section-8-7.5">A legacy PCEP speaker that does not recognize the P flag in the
          LSP object would ignore it in accordance with <xref target="RFC8231" format="default" sectionFormat="of" derivedContent="RFC8231"/>.</li>
      </ul>
      <t indent="0" pn="section-8-8">It is assumed that the label range to be used by a PCE is known and
      set on both PCEP peers. The exact mechanism is out of the scope of <xref target="RFC9050" format="default" sectionFormat="of" derivedContent="RFC9050"/> and this document. Note that the specific BSID could
      be from the PCE-controlled or the PCC-controlled label space. The PCE
      can directly allocate the label from the PCE-controlled label space
      using P=1 as described above, whereas the PCE can request the allocation
      of a specific BSID from the PCC-controlled label space with P=0 as
      described in <xref target="Operation" format="default" sectionFormat="of" derivedContent="Section 5"/>.</t>
      <t indent="0" pn="section-8-9">Note that the P flag in the LSP object <bcp14>SHOULD NOT</bcp14> be set to 1
      without the presence of TE-PATH-BINDING TLV or any other future TLV
      defined for PCE allocation. On receipt of such an LSP object, the P flag
      is ignored. The presence of TE-PATH-BINDING TLV with P=1 indicates the
      allocation is for the binding label/SID. In the future, some other TLV
      (such as one defined in <xref target="I-D.ietf-pce-sr-path-segment" format="default" sectionFormat="of" derivedContent="PCEP-SR"/>)
      could also be used alongside P=1 to indicate allocation of a different
      attribute. A future document should not attempt to assign semantics to
      P=1 without limiting the scope to one that both PCEP peers can agree on.</t>
    </section>
    <section anchor="Security" numbered="true" toc="include" removeInRFC="false" pn="section-9">
      <name slugifiedName="name-security-considerations">Security Considerations</name>
      <t indent="0" pn="section-9-1">The security considerations described in <xref target="RFC5440" format="default" sectionFormat="of" derivedContent="RFC5440"/>,
      <xref target="RFC8231" format="default" sectionFormat="of" derivedContent="RFC8231"/>, <xref target="RFC8281" format="default" sectionFormat="of" derivedContent="RFC8281"/>, <xref target="RFC8664" format="default" sectionFormat="of" derivedContent="RFC8664"/>, and <xref target="RFC9050" format="default" sectionFormat="of" derivedContent="RFC9050"/> are applicable to this
      specification. No additional security measure is required.</t>
      <t indent="0" pn="section-9-2">As described in <xref target="RFC8402" format="default" sectionFormat="of" derivedContent="RFC8402"/> and <xref target="RFC8664" format="default" sectionFormat="of" derivedContent="RFC8664"/>, SR intrinsically involves an entity (whether
      head-end or a central network controller) controlling and instantiating
      paths in the network without the involvement of (other) nodes along
      those paths. Binding SIDs are in effect shorthand aliases for longer
      path representations, and the alias expansion is in principle known only
      by the node that acts on it. In this document, the expansion of the
      alias is shared between PCC and PCE, and rogue actions by either PCC or
      PCE could result in shifting or misdirecting traffic in ways that are
      hard for other nodes to detect. In particular, when a PCE propagates
      paths of the form {A, B, BSID} to other entities, the BSID values are
      opaque, and a rogue PCE can substitute a BSID from a different LSP in
      such paths to move traffic without the recipient of the path knowing the
      ultimate destination.</t>
      <t indent="0" pn="section-9-3">The case of BT=3 provides additional opportunities for malfeasance,
      as it purports to convey information about internal SRv6 SID Structure.
      There is no mechanism defined to validate this internal structure
      information, and mischaracterizing the division of bits into locator
      block, locator node, function, and argument can result in different
      interpretation of the bits by PCC and PCE. Most notably, shifting bits
      into or out of the "argument" is a direct vector for affecting
      processing, but other attacks are also possible.</t>
      <t indent="0" pn="section-9-4">Thus, as per <xref target="RFC8231" format="default" sectionFormat="of" derivedContent="RFC8231"/>, it is
      <bcp14>RECOMMENDED</bcp14> that these PCEP extensions only be activated
      on authenticated and encrypted sessions across PCEs and PCCs belonging
      to the same administrative authority, using Transport Layer Security
      (TLS) <xref target="RFC8253" format="default" sectionFormat="of" derivedContent="RFC8253"/>, as per the
      recommendations and best current practices in RFC 9325 <xref target="BCP195" format="default" sectionFormat="of" derivedContent="BCP195"/>
      (unless explicitly set aside in
      <xref target="RFC8253" format="default" sectionFormat="of" derivedContent="RFC8253"/>).</t>
    </section>
    <section toc="include" numbered="true" removeInRFC="false" pn="section-10">
      <name slugifiedName="name-manageability-consideration">Manageability Considerations</name>
      <t indent="0" pn="section-10-1">All manageability requirements and considerations listed in <xref format="default" target="RFC5440" sectionFormat="of" derivedContent="RFC5440"/>, <xref format="default" target="RFC8231" sectionFormat="of" derivedContent="RFC8231"/>, and <xref target="RFC8664" format="default" sectionFormat="of" derivedContent="RFC8664"/> apply to PCEP protocol extensions defined in this
      document. In addition, requirements and considerations listed in this
      section apply.</t>
      <section toc="include" numbered="true" removeInRFC="false" pn="section-10.1">
        <name slugifiedName="name-control-of-function-and-pol">Control of Function and Policy</name>
        <t indent="0" pn="section-10.1-1">A PCC implementation <bcp14>SHOULD</bcp14> allow the operator to configure the
        policy the PCC needs to apply when allocating the binding
        label/SID.</t>
        <t indent="0" pn="section-10.1-2">If BT is set to 2, the operator needs to have local policy set to
        decide the SID structure and the SRv6 Endpoint Behavior of the
        BSID.</t>
      </section>
      <section toc="include" numbered="true" removeInRFC="false" pn="section-10.2">
        <name slugifiedName="name-information-and-data-models">Information and Data Models</name>
        <t indent="0" pn="section-10.2-1">The PCEP YANG module <xref target="I-D.ietf-pce-pcep-yang" format="default" sectionFormat="of" derivedContent="PCEP-YANG"/> will
        be extended to include policy configuration for binding label/SID
        allocation.</t>
      </section>
      <section toc="include" numbered="true" removeInRFC="false" pn="section-10.3">
        <name slugifiedName="name-liveness-detection-and-moni">Liveness Detection and Monitoring</name>
        <t indent="0" pn="section-10.3-1">The mechanisms defined in this document do not imply any new
        liveness detection and monitoring requirements in addition to those
        already listed in <xref format="default" target="RFC5440" sectionFormat="of" derivedContent="RFC5440"/>.</t>
      </section>
      <section toc="include" numbered="true" removeInRFC="false" pn="section-10.4">
        <name slugifiedName="name-verify-correct-operations">Verify Correct Operations</name>
        <t indent="0" pn="section-10.4-1">The mechanisms defined in this document do not imply any new
        operation verification requirements in addition to those already
        listed in <xref format="default" target="RFC5440" sectionFormat="of" derivedContent="RFC5440"/>,
        <xref format="default" target="RFC8231" sectionFormat="of" derivedContent="RFC8231"/>, and <xref target="RFC8664" format="default" sectionFormat="of" derivedContent="RFC8664"/>.</t>
      </section>
      <section toc="include" numbered="true" removeInRFC="false" pn="section-10.5">
        <name slugifiedName="name-requirements-on-other-proto">Requirements on Other Protocols</name>
        <t indent="0" pn="section-10.5-1">The mechanisms defined in this document do not imply any new
        requirements on other protocols.</t>
      </section>
      <section toc="include" numbered="true" removeInRFC="false" pn="section-10.6">
        <name slugifiedName="name-impact-on-network-operation">Impact on Network Operations</name>
        <t indent="0" pn="section-10.6-1">The mechanisms defined in <xref format="default" target="RFC5440" sectionFormat="of" derivedContent="RFC5440"/>, <xref format="default" target="RFC8231" sectionFormat="of" derivedContent="RFC8231"/>, and <xref target="RFC8664" format="default" sectionFormat="of" derivedContent="RFC8664"/> also apply to the
        PCEP extensions defined in this document.</t>
      </section>
    </section>
    <section anchor="IANA" numbered="true" toc="include" removeInRFC="false" pn="section-11">
      <name slugifiedName="name-iana-considerations">IANA Considerations</name>
      <t indent="0" pn="section-11-1">IANA has allocated code points for the protocol elements described in this document in the "Path Computation Element Protocol (PCEP) Numbers" registry group.</t>
      <section anchor="TLV" numbered="true" toc="include" removeInRFC="false" pn="section-11.1">
        <name slugifiedName="name-pcep-tlv-type-indicators">PCEP TLV Type Indicators</name>
        <t indent="0" pn="section-11.1-1">This document defines a new PCEP TLV. IANA has allocated the following in the  "PCEP TLV Type Indicators" registry within the PCEP Numbers registry group:</t>
        <table anchor="TLV-Type" align="center" pn="table-1">
          <thead>
            <tr>
              <th align="center" colspan="1" rowspan="1">Value</th>
              <th align="left" colspan="1" rowspan="1">Description</th>
              <th align="left" colspan="1" rowspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td align="center" colspan="1" rowspan="1">55</td>
              <td align="left" colspan="1" rowspan="1">TE-PATH-BINDING</td>
              <td align="left" colspan="1" rowspan="1">RFC 9604</td>
            </tr>
          </tbody>
        </table>
        <section anchor="IANA-TLV" numbered="true" toc="include" removeInRFC="false" pn="section-11.1.1">
          <name slugifiedName="name-te-path-binding-tlv-2">TE-PATH-BINDING TLV</name>
          <t indent="0" pn="section-11.1.1-1">IANA has created the "TE-PATH-BINDING TLV BT Field" registry 
          to manage the values of the binding type field in the
          TE-PATH-BINDING TLV. Initial values are shown
          below. New values are assigned by Standards Action <xref target="RFC8126" format="default" sectionFormat="of" derivedContent="RFC8126"/>.</t>
          <table anchor="BT" align="center" pn="table-2">
            <thead>
              <tr>
                <th align="center" colspan="1" rowspan="1">Value</th>
                <th align="left" colspan="1" rowspan="1">Description</th>
                <th align="left" colspan="1" rowspan="1">Reference</th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td align="center" colspan="1" rowspan="1">0</td>
                <td align="left" colspan="1" rowspan="1">MPLS Label</td>
                <td align="left" colspan="1" rowspan="1">RFC 9604</td>
              </tr>
              <tr>
                <td align="center" colspan="1" rowspan="1">1</td>
                <td align="left" colspan="1" rowspan="1">MPLS Label Stack Entry</td>
                <td align="left" colspan="1" rowspan="1">RFC 9604</td>
              </tr>
              <tr>
                <td align="center" colspan="1" rowspan="1">2</td>
                <td align="left" colspan="1" rowspan="1">SRv6 SID</td>
                <td align="left" colspan="1" rowspan="1">RFC 9604</td>
              </tr>
              <tr>
                <td align="center" colspan="1" rowspan="1">3</td>
                <td align="left" colspan="1" rowspan="1">SRv6 SID with Behavior and Structure</td>
                <td align="left" colspan="1" rowspan="1">RFC 9604</td>
              </tr>
              <tr>
                <td align="center" colspan="1" rowspan="1">4-255</td>
                <td align="left" colspan="1" rowspan="1">Unassigned</td>
                <td align="left" colspan="1" rowspan="1"/>
              </tr>
            </tbody>
          </table>
          <t indent="0" pn="section-11.1.1-3">IANA has created a new "TE-PATH-BINDING
          TLV Flag Field" registry to manage the Flag field in the TE-PATH-BINDING TLV.
          New values are to be assigned by Standards Action <xref target="RFC8126" format="default" sectionFormat="of" derivedContent="RFC8126"/>. Each bit should be tracked with
          the following qualities:</t>
          <ul spacing="compact" bare="false" empty="false" indent="3" pn="section-11.1.1-4">
            <li pn="section-11.1.1-4.1">Bit number (count from 0 as the most significant bit)</li>
            <li pn="section-11.1.1-4.2">Description</li>
            <li pn="section-11.1.1-4.3">Reference</li>
          </ul>
          <table anchor="BF" align="center" pn="table-3">
            <thead>
              <tr>
                <th align="center" colspan="1" rowspan="1">Bit</th>
                <th align="left" colspan="1" rowspan="1">Description</th>
                <th align="left" colspan="1" rowspan="1">Reference</th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td align="center" colspan="1" rowspan="1">0</td>
                <td align="left" colspan="1" rowspan="1">R (Removal)</td>
                <td align="left" colspan="1" rowspan="1">RFC 9604</td>
              </tr>
              <tr>
                <td align="center" colspan="1" rowspan="1">1-7</td>
                <td align="left" colspan="1" rowspan="1">Unassigned</td>
                <td align="left" colspan="1" rowspan="1"/>
              </tr>
            </tbody>
          </table>
        </section>
      </section>
      <section anchor="LSP" numbered="true" toc="include" removeInRFC="false" pn="section-11.2">
        <name slugifiedName="name-lsp-object">LSP Object</name>
        <t indent="0" pn="section-11.2-1">IANA has allocated a 
        code point in the "LSP Object Flag Field" registry for the new P
        flag as follows:</t>
        <table anchor="LSP-Flag" align="center" pn="table-4">
          <thead>
            <tr>
              <th align="center" colspan="1" rowspan="1">Bit</th>
              <th align="left" colspan="1" rowspan="1">Description</th>
              <th align="left" colspan="1" rowspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td align="center" colspan="1" rowspan="1">0</td>
              <td align="left" colspan="1" rowspan="1">PCE-allocation</td>
              <td align="left" colspan="1" rowspan="1">RFC 9604</td>
            </tr>
          </tbody>
        </table>
      </section>
      <section anchor="Error-Type" numbered="true" toc="include" removeInRFC="false" pn="section-11.3">
        <name slugifiedName="name-pcep-error-type-and-value">PCEP Error Type and Value</name>
        <t indent="0" pn="section-11.3-1">This document defines a new Error-Type and associated Error-values
        for the PCErr message. IANA has allocated a new Error-Type
        and Error-values within the "PCEP-ERROR Object Error Types and Values"
        registry of the PCEP Numbers registry group, as follows:</t>
        <table anchor="Error" align="center" pn="table-5">
          <thead>
            <tr>
              <th align="left" colspan="1" rowspan="1">Error-Type</th>
              <th align="left" colspan="1" rowspan="1">Meaning</th>
              <th align="left" colspan="1" rowspan="1">Error-value</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td rowspan="6" align="left" colspan="1">32</td>
              <td rowspan="6" align="left" colspan="1">Binding label/SID failure</td>
              <td align="left" colspan="1" rowspan="1">0: Unassigned</td>
            </tr>
            <tr>
              <td align="left" colspan="1" rowspan="1">1: Invalid SID</td>
            </tr>
            <tr>
              <td align="left" colspan="1" rowspan="1">2: Unable to allocate the specified binding value</td>
            </tr>
            <tr>
              <td align="left" colspan="1" rowspan="1">3: Unable to allocate a new binding label/SID</td>
            </tr>
            <tr>
              <td align="left" colspan="1" rowspan="1">4: Unable to remove the binding value</td>
            </tr>
            <tr>
              <td align="left" colspan="1" rowspan="1">5: Inconsistent binding types</td>
            </tr>
          </tbody>
        </table>
      </section>
    </section>
  </middle>
  <back>
    <displayreference target="I-D.ietf-pce-pcep-yang" to="PCEP-YANG"/>
    <displayreference target="I-D.ietf-pce-controlled-id-space" to="PCE-ID-SPACE"/>
    <displayreference target="I-D.ietf-pce-sr-path-segment" to="PCEP-SR"/>
    <references pn="section-12">
      <name slugifiedName="name-references">References</name>
      <references pn="section-12.1">
        <name slugifiedName="name-normative-references">Normative References</name>
        <referencegroup anchor="BCP195" target="https://www.rfc-editor.org/info/bcp195" derivedAnchor="BCP195">
          <reference anchor="RFC8996" target="https://www.rfc-editor.org/info/rfc8996" quoteTitle="true">
            <front>
              <title>Deprecating TLS 1.0 and TLS 1.1</title>
              <author fullname="K. Moriarty" initials="K." surname="Moriarty"/>
              <author fullname="S. Farrell" initials="S." surname="Farrell"/>
              <date month="March" year="2021"/>
              <abstract>
                <t indent="0">This document formally deprecates Transport Layer Security (TLS) versions 1.0 (RFC 2246) and 1.1 (RFC 4346). Accordingly, those documents have been moved to Historic status. These versions lack support for current and recommended cryptographic algorithms and mechanisms, and various government and industry profiles of applications using TLS now mandate avoiding these old TLS versions. TLS version 1.2 became the recommended version for IETF protocols in 2008 (subsequently being obsoleted by TLS version 1.3 in 2018), providing sufficient time to transition away from older versions. Removing support for older versions from implementations reduces the attack surface, reduces opportunity for misconfiguration, and streamlines library and product maintenance.</t>
                <t indent="0">This document also deprecates Datagram TLS (DTLS) version 1.0 (RFC 4347) but not DTLS version 1.2, and there is no DTLS version 1.1.</t>
                <t indent="0">This document updates many RFCs that normatively refer to TLS version 1.0 or TLS version 1.1, as described herein. This document also updates the best practices for TLS usage in RFC 7525; hence, it is part of BCP 195.</t>
              </abstract>
            </front>
            <seriesInfo name="BCP" value="195"/>
            <seriesInfo name="RFC" value="8996"/>
            <seriesInfo name="DOI" value="10.17487/RFC8996"/>
          </reference>
          <reference anchor="RFC9325" target="https://www.rfc-editor.org/info/rfc9325" quoteTitle="true">
            <front>
              <title>Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)</title>
              <author fullname="Y. Sheffer" initials="Y." surname="Sheffer"/>
              <author fullname="P. Saint-Andre" initials="P." surname="Saint-Andre"/>
              <author fullname="T. Fossati" initials="T." surname="Fossati"/>
              <date month="November" year="2022"/>
              <abstract>
                <t indent="0">Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) are used to protect data exchanged over a wide range of application protocols and can also form the basis for secure transport protocols. Over the years, the industry has witnessed several serious attacks on TLS and DTLS, including attacks on the most commonly used cipher suites and their modes of operation. This document provides the latest recommendations for ensuring the security of deployed services that use TLS and DTLS. These recommendations are applicable to the majority of use cases.</t>
                <t indent="0">RFC 7525, an earlier version of the TLS recommendations, was published when the industry was transitioning to TLS 1.2. Years later, this transition is largely complete, and TLS 1.3 is widely available. This document updates the guidance given the new environment and obsoletes RFC 7525. In addition, this document updates RFCs 5288 and 6066 in view of recent attacks.</t>
              </abstract>
            </front>
            <seriesInfo name="BCP" value="195"/>
            <seriesInfo name="RFC" value="9325"/>
            <seriesInfo name="DOI" value="10.17487/RFC9325"/>
          </reference>
        </referencegroup>
        <reference anchor="RFC2119" target="https://www.rfc-editor.org/info/rfc2119" quoteTitle="true" derivedAnchor="RFC2119">
          <front>
            <title>Key words for use in RFCs to Indicate Requirement Levels</title>
            <author fullname="S. Bradner" initials="S." surname="Bradner"/>
            <date month="March" year="1997"/>
            <abstract>
              <t indent="0">In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="14"/>
          <seriesInfo name="RFC" value="2119"/>
          <seriesInfo name="DOI" value="10.17487/RFC2119"/>
        </reference>
        <reference anchor="RFC3032" target="https://www.rfc-editor.org/info/rfc3032" quoteTitle="true" derivedAnchor="RFC3032">
          <front>
            <title>MPLS Label Stack Encoding</title>
            <author fullname="E. Rosen" initials="E." surname="Rosen"/>
            <author fullname="D. Tappan" initials="D." surname="Tappan"/>
            <author fullname="G. Fedorkow" initials="G." surname="Fedorkow"/>
            <author fullname="Y. Rekhter" initials="Y." surname="Rekhter"/>
            <author fullname="D. Farinacci" initials="D." surname="Farinacci"/>
            <author fullname="T. Li" initials="T." surname="Li"/>
            <author fullname="A. Conta" initials="A." surname="Conta"/>
            <date month="January" year="2001"/>
            <abstract>
              <t indent="0">This document specifies the encoding to be used by an LSR in order to transmit labeled packets on Point-to-Point Protocol (PPP) data links, on LAN data links, and possibly on other data links as well. This document also specifies rules and procedures for processing the various fields of the label stack encoding. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="3032"/>
          <seriesInfo name="DOI" value="10.17487/RFC3032"/>
        </reference>
        <reference anchor="RFC5440" target="https://www.rfc-editor.org/info/rfc5440" quoteTitle="true" derivedAnchor="RFC5440">
          <front>
            <title>Path Computation Element (PCE) Communication Protocol (PCEP)</title>
            <author fullname="JP. Vasseur" initials="JP." role="editor" surname="Vasseur"/>
            <author fullname="JL. Le Roux" initials="JL." role="editor" surname="Le Roux"/>
            <date month="March" year="2009"/>
            <abstract>
              <t indent="0">This document specifies the Path Computation Element (PCE) Communication Protocol (PCEP) for communications between a Path Computation Client (PCC) and a PCE, or between two PCEs. Such interactions include path computation requests and path computation replies as well as notifications of specific states related to the use of a PCE in the context of Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineering. PCEP is designed to be flexible and extensible so as to easily allow for the addition of further messages and objects, should further requirements be expressed in the future. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="5440"/>
          <seriesInfo name="DOI" value="10.17487/RFC5440"/>
        </reference>
        <reference anchor="RFC5462" target="https://www.rfc-editor.org/info/rfc5462" quoteTitle="true" derivedAnchor="RFC5462">
          <front>
            <title>Multiprotocol Label Switching (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic Class" Field</title>
            <author fullname="L. Andersson" initials="L." surname="Andersson"/>
            <author fullname="R. Asati" initials="R." surname="Asati"/>
            <date month="February" year="2009"/>
            <abstract>
              <t indent="0">The early Multiprotocol Label Switching (MPLS) documents defined the form of the MPLS label stack entry. This includes a three-bit field called the "EXP field". The exact use of this field was not defined by these documents, except to state that it was to be "reserved for experimental use".</t>
              <t indent="0">Although the intended use of the EXP field was as a "Class of Service" (CoS) field, it was not named a CoS field by these early documents because the use of such a CoS field was not considered to be sufficiently defined. Today a number of standards documents define its usage as a CoS field.</t>
              <t indent="0">To avoid misunderstanding about how this field may be used, it has become increasingly necessary to rename this field. This document changes the name of the field to the "Traffic Class field" ("TC field"). In doing so, it also updates documents that define the current use of the EXP field. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="5462"/>
          <seriesInfo name="DOI" value="10.17487/RFC5462"/>
        </reference>
        <reference anchor="RFC8126" target="https://www.rfc-editor.org/info/rfc8126" quoteTitle="true" derivedAnchor="RFC8126">
          <front>
            <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
            <author fullname="M. Cotton" initials="M." surname="Cotton"/>
            <author fullname="B. Leiba" initials="B." surname="Leiba"/>
            <author fullname="T. Narten" initials="T." surname="Narten"/>
            <date month="June" year="2017"/>
            <abstract>
              <t indent="0">Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA).</t>
              <t indent="0">To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry.</t>
              <t indent="0">This is the third edition of this document; it obsoletes RFC 5226.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="26"/>
          <seriesInfo name="RFC" value="8126"/>
          <seriesInfo name="DOI" value="10.17487/RFC8126"/>
        </reference>
        <reference anchor="RFC8174" target="https://www.rfc-editor.org/info/rfc8174" quoteTitle="true" derivedAnchor="RFC8174">
          <front>
            <title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title>
            <author fullname="B. Leiba" initials="B." surname="Leiba"/>
            <date month="May" year="2017"/>
            <abstract>
              <t indent="0">RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="14"/>
          <seriesInfo name="RFC" value="8174"/>
          <seriesInfo name="DOI" value="10.17487/RFC8174"/>
        </reference>
        <reference anchor="RFC8231" target="https://www.rfc-editor.org/info/rfc8231" quoteTitle="true" derivedAnchor="RFC8231">
          <front>
            <title>Path Computation Element Communication Protocol (PCEP) Extensions for Stateful PCE</title>
            <author fullname="E. Crabbe" initials="E." surname="Crabbe"/>
            <author fullname="I. Minei" initials="I." surname="Minei"/>
            <author fullname="J. Medved" initials="J." surname="Medved"/>
            <author fullname="R. Varga" initials="R." surname="Varga"/>
            <date month="September" year="2017"/>
            <abstract>
              <t indent="0">The Path Computation Element Communication Protocol (PCEP) provides mechanisms for Path Computation Elements (PCEs) to perform path computations in response to Path Computation Client (PCC) requests.</t>
              <t indent="0">Although PCEP explicitly makes no assumptions regarding the information available to the PCE, it also makes no provisions for PCE control of timing and sequence of path computations within and across PCEP sessions. This document describes a set of extensions to PCEP to enable stateful control of MPLS-TE and GMPLS Label Switched Paths (LSPs) via PCEP.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8231"/>
          <seriesInfo name="DOI" value="10.17487/RFC8231"/>
        </reference>
        <reference anchor="RFC8253" target="https://www.rfc-editor.org/info/rfc8253" quoteTitle="true" derivedAnchor="RFC8253">
          <front>
            <title>PCEPS: Usage of TLS to Provide a Secure Transport for the Path Computation Element Communication Protocol (PCEP)</title>
            <author fullname="D. Lopez" initials="D." surname="Lopez"/>
            <author fullname="O. Gonzalez de Dios" initials="O." surname="Gonzalez de Dios"/>
            <author fullname="Q. Wu" initials="Q." surname="Wu"/>
            <author fullname="D. Dhody" initials="D." surname="Dhody"/>
            <date month="October" year="2017"/>
            <abstract>
              <t indent="0">The Path Computation Element Communication Protocol (PCEP) defines the mechanisms for the communication between a Path Computation Client (PCC) and a Path Computation Element (PCE), or among PCEs. This document describes PCEPS -- the usage of Transport Layer Security (TLS) to provide a secure transport for PCEP. The additional security mechanisms are provided by the transport protocol supporting PCEP; therefore, they do not affect the flexibility and extensibility of PCEP.</t>
              <t indent="0">This document updates RFC 5440 in regards to the PCEP initialization phase procedures.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8253"/>
          <seriesInfo name="DOI" value="10.17487/RFC8253"/>
        </reference>
        <reference anchor="RFC8281" target="https://www.rfc-editor.org/info/rfc8281" quoteTitle="true" derivedAnchor="RFC8281">
          <front>
            <title>Path Computation Element Communication Protocol (PCEP) Extensions for PCE-Initiated LSP Setup in a Stateful PCE Model</title>
            <author fullname="E. Crabbe" initials="E." surname="Crabbe"/>
            <author fullname="I. Minei" initials="I." surname="Minei"/>
            <author fullname="S. Sivabalan" initials="S." surname="Sivabalan"/>
            <author fullname="R. Varga" initials="R." surname="Varga"/>
            <date month="December" year="2017"/>
            <abstract>
              <t indent="0">The Path Computation Element Communication Protocol (PCEP) provides mechanisms for Path Computation Elements (PCEs) to perform path computations in response to Path Computation Client (PCC) requests.</t>
              <t indent="0">The extensions for stateful PCE provide active control of Multiprotocol Label Switching (MPLS) Traffic Engineering Label Switched Paths (TE LSPs) via PCEP, for a model where the PCC delegates control over one or more locally configured LSPs to the PCE. This document describes the creation and deletion of PCE-initiated LSPs under the stateful PCE model.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8281"/>
          <seriesInfo name="DOI" value="10.17487/RFC8281"/>
        </reference>
        <reference anchor="RFC8402" target="https://www.rfc-editor.org/info/rfc8402" quoteTitle="true" derivedAnchor="RFC8402">
          <front>
            <title>Segment Routing Architecture</title>
            <author fullname="C. Filsfils" initials="C." role="editor" surname="Filsfils"/>
            <author fullname="S. Previdi" initials="S." role="editor" surname="Previdi"/>
            <author fullname="L. Ginsberg" initials="L." surname="Ginsberg"/>
            <author fullname="B. Decraene" initials="B." surname="Decraene"/>
            <author fullname="S. Litkowski" initials="S." surname="Litkowski"/>
            <author fullname="R. Shakir" initials="R." surname="Shakir"/>
            <date month="July" year="2018"/>
            <abstract>
              <t indent="0">Segment Routing (SR) leverages the source routing paradigm. A node steers a packet through an ordered list of instructions, called "segments". A segment can represent any instruction, topological or service based. A segment can have a semantic local to an SR node or global within an SR domain. SR provides a mechanism that allows a flow to be restricted to a specific topological path, while maintaining per-flow state only at the ingress node(s) to the SR domain.</t>
              <t indent="0">SR can be directly applied to the MPLS architecture with no change to the forwarding plane. A segment is encoded as an MPLS label. An ordered list of segments is encoded as a stack of labels. The segment to process is on the top of the stack. Upon completion of a segment, the related label is popped from the stack.</t>
              <t indent="0">SR can be applied to the IPv6 architecture, with a new type of routing header. A segment is encoded as an IPv6 address. An ordered list of segments is encoded as an ordered list of IPv6 addresses in the routing header. The active segment is indicated by the Destination Address (DA) of the packet. The next active segment is indicated by a pointer in the new routing header.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8402"/>
          <seriesInfo name="DOI" value="10.17487/RFC8402"/>
        </reference>
        <reference anchor="RFC8664" target="https://www.rfc-editor.org/info/rfc8664" quoteTitle="true" derivedAnchor="RFC8664">
          <front>
            <title>Path Computation Element Communication Protocol (PCEP) Extensions for Segment Routing</title>
            <author fullname="S. Sivabalan" initials="S." surname="Sivabalan"/>
            <author fullname="C. Filsfils" initials="C." surname="Filsfils"/>
            <author fullname="J. Tantsura" initials="J." surname="Tantsura"/>
            <author fullname="W. Henderickx" initials="W." surname="Henderickx"/>
            <author fullname="J. Hardwick" initials="J." surname="Hardwick"/>
            <date month="December" year="2019"/>
            <abstract>
              <t indent="0">Segment Routing (SR) enables any head-end node to select any path without relying on a hop-by-hop signaling technique (e.g., LDP or RSVP-TE). It depends only on "segments" that are advertised by link-state Interior Gateway Protocols (IGPs). An SR path can be derived from a variety of mechanisms, including an IGP Shortest Path Tree (SPT), an explicit configuration, or a Path Computation Element (PCE). This document specifies extensions to the Path Computation Element Communication Protocol (PCEP) that allow a stateful PCE to compute and initiate Traffic-Engineering (TE) paths, as well as a Path Computation Client (PCC) to request a path subject to certain constraints and optimization criteria in SR networks.</t>
              <t indent="0">This document updates RFC 8408.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8664"/>
          <seriesInfo name="DOI" value="10.17487/RFC8664"/>
        </reference>
        <reference anchor="RFC8986" target="https://www.rfc-editor.org/info/rfc8986" quoteTitle="true" derivedAnchor="RFC8986">
          <front>
            <title>Segment Routing over IPv6 (SRv6) Network Programming</title>
            <author fullname="C. Filsfils" initials="C." role="editor" surname="Filsfils"/>
            <author fullname="P. Camarillo" initials="P." role="editor" surname="Camarillo"/>
            <author fullname="J. Leddy" initials="J." surname="Leddy"/>
            <author fullname="D. Voyer" initials="D." surname="Voyer"/>
            <author fullname="S. Matsushima" initials="S." surname="Matsushima"/>
            <author fullname="Z. Li" initials="Z." surname="Li"/>
            <date month="February" year="2021"/>
            <abstract>
              <t indent="0">The Segment Routing over IPv6 (SRv6) Network Programming framework enables a network operator or an application to specify a packet processing program by encoding a sequence of instructions in the IPv6 packet header.</t>
              <t indent="0">Each instruction is implemented on one or several nodes in the network and identified by an SRv6 Segment Identifier in the packet.</t>
              <t indent="0">This document defines the SRv6 Network Programming concept and specifies the base set of SRv6 behaviors that enables the creation of interoperable overlays with underlay optimization.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8986"/>
          <seriesInfo name="DOI" value="10.17487/RFC8986"/>
        </reference>
        <reference anchor="RFC9050" target="https://www.rfc-editor.org/info/rfc9050" quoteTitle="true" derivedAnchor="RFC9050">
          <front>
            <title>Path Computation Element Communication Protocol (PCEP) Procedures and Extensions for Using the PCE as a Central Controller (PCECC) of LSPs</title>
            <author fullname="Z. Li" initials="Z." surname="Li"/>
            <author fullname="S. Peng" initials="S." surname="Peng"/>
            <author fullname="M. Negi" initials="M." surname="Negi"/>
            <author fullname="Q. Zhao" initials="Q." surname="Zhao"/>
            <author fullname="C. Zhou" initials="C." surname="Zhou"/>
            <date month="July" year="2021"/>
            <abstract>
              <t indent="0">The Path Computation Element (PCE) is a core component of Software-Defined Networking (SDN) systems.</t>
              <t indent="0">A PCE as a Central Controller (PCECC) can simplify the processing of a distributed control plane by blending it with elements of SDN and without necessarily completely replacing it. Thus, the Label Switched Path (LSP) can be calculated/set up/initiated and the label-forwarding entries can also be downloaded through a centralized PCE server to each network device along the path while leveraging the existing PCE technologies as much as possible.</t>
              <t indent="0">This document specifies the procedures and Path Computation Element Communication Protocol (PCEP) extensions for using the PCE as the central controller for provisioning labels along the path of the static LSP.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="9050"/>
          <seriesInfo name="DOI" value="10.17487/RFC9050"/>
        </reference>
        <reference anchor="RFC9603" target="https://www.rfc-editor.org/info/rfc9603" quoteTitle="true" derivedAnchor="RFC9603">
          <front>
            <title>Path Computation Element Communication Protocol (PCEP) Extensions for IPv6 Segment Routing</title>
            <author fullname="C. Li" initials="C." role="editor" surname="Li"/>
            <author fullname="P. Kaladharan" initials="P." surname="Kaladharan"/>
            <author fullname="S. Sivabalan" initials="S." surname="Sivabalan"/>
            <author fullname="M. Koldychev" initials="M." surname="Koldychev"/>
            <author fullname="Y. Zhu" initials="Y." surname="Zhu"/>
            <date month="July" year="2024"/>
            <abstract>
              <t indent="0">Segment Routing (SR) can be used to steer packets through a network using the IPv6 or MPLS data plane, employing the source routing paradigm.</t>
              <t indent="0">An SR Path can be derived from a variety of mechanisms, including an IGP Shortest Path Tree (SPT), explicit configuration, or a Path Computation Element (PCE).</t>
              <t indent="0">Since SR can be applied to both MPLS and IPv6 data planes, a PCE should be able to compute an SR Path for both MPLS and IPv6 data planes. The Path Computation Element Communication Protocol (PCEP) extension and mechanisms to support SR-MPLS have been defined. This document outlines the necessary extensions to support SR for the IPv6 data plane within PCEP.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="9603"/>
          <seriesInfo name="DOI" value="10.17487/RFC9603"/>
        </reference>
      </references>
      <references pn="section-12.2">
        <name slugifiedName="name-informative-references">Informative References</name>
        <reference anchor="I-D.ietf-pce-controlled-id-space" target="https://datatracker.ietf.org/doc/html/draft-ietf-pce-controlled-id-space-00" quoteTitle="true" derivedAnchor="PCE-ID-SPACE">
          <front>
            <title>Path Computation Element Communication Protocol (PCEP) extension to advertise the PCE Controlled Identifier Space</title>
            <author initials="C." surname="Li" fullname="Cheng Li">
              <organization showOnFrontPage="true">Huawei Technologies</organization>
            </author>
            <author initials="H." surname="Shi" fullname="Hang Shi" role="editor">
              <organization showOnFrontPage="true">Huawei Technologies</organization>
            </author>
            <author initials="A." surname="Wang" fullname="Aijun Wang">
              <organization showOnFrontPage="true">China Telecom</organization>
            </author>
            <author initials="W." surname="Cheng" fullname="Weiqiang Cheng">
              <organization showOnFrontPage="true">China Mobile</organization>
            </author>
            <author initials="C." surname="Zhou" fullname="Chao Zhou">
              <organization showOnFrontPage="true">HPE</organization>
            </author>
            <date month="June" day="4" year="2024"/>
          </front>
          <seriesInfo name="Internet-Draft" value="draft-ietf-pce-controlled-id-space-00"/>
          <refcontent>Work in Progress</refcontent>
        </reference>
        <reference anchor="I-D.ietf-pce-sr-path-segment" target="https://datatracker.ietf.org/doc/html/draft-ietf-pce-sr-path-segment-09" quoteTitle="true" derivedAnchor="PCEP-SR">
          <front>
            <title>Path Computation Element Communication Protocol (PCEP) Extension for Path Segment in Segment Routing (SR)</title>
            <author initials="C." surname="Li" fullname="Cheng Li">
              <organization showOnFrontPage="true">Huawei Technologies</organization>
            </author>
            <author initials="M." surname="Chen" fullname="Mach Chen">
              <organization showOnFrontPage="true">Huawei Technologies</organization>
            </author>
            <author initials="W." surname="Cheng" fullname="Weiqiang Cheng">
              <organization showOnFrontPage="true">China Mobile</organization>
            </author>
            <author initials="R." surname="Gandhi" fullname="Rakesh Gandhi">
              <organization showOnFrontPage="true">Cisco Systems, Inc.</organization>
            </author>
            <author initials="Q." surname="Xiong" fullname="Quan Xiong">
              <organization showOnFrontPage="true">ZTE Corporation</organization>
            </author>
            <date month="February" day="26" year="2024"/>
            <abstract>
              <t indent="0">   The Path Computation Element (PCE) provides path computation
   functions in support of traffic engineering in Multiprotocol Label
   Switching (MPLS) and Generalized MPLS (GMPLS) networks.

   The Source Packet Routing in Networking (SPRING) architecture
   describes how Segment Routing (SR) can be used to steer packets
   through an IPv6 or MPLS network using the source routing paradigm.  A
   Segment Routed Path can be derived from a variety of mechanisms,
   including an IGP Shortest Path Tree (SPT), explicit configuration, or
   a Path Computation Element (PCE).

   Path identification is needed for several use cases such as
   performance measurement in Segment Routing (SR) network.  This
   document specifies extensions to the Path Computation Element
   Communication Protocol (PCEP) to support requesting, replying,
   reporting and updating the Path Segment ID (Path SID) between PCEP
   speakers.

              </t>
            </abstract>
          </front>
          <seriesInfo name="Internet-Draft" value="draft-ietf-pce-sr-path-segment-09"/>
          <refcontent>Work in Progress</refcontent>
        </reference>
        <reference anchor="I-D.ietf-pce-pcep-yang" target="https://datatracker.ietf.org/doc/html/draft-ietf-pce-pcep-yang-25" quoteTitle="true" derivedAnchor="PCEP-YANG">
          <front>
            <title>A YANG Data Model for Path Computation Element Communications Protocol (PCEP)</title>
            <author initials="D." surname="Dhody" fullname="Dhruv Dhody" role="editor">
              <organization showOnFrontPage="true">Huawei</organization>
            </author>
            <author initials="V." surname="Beeram" fullname="Vishnu Pavan Beeram">
              <organization showOnFrontPage="true">Juniper Networks</organization>
            </author>
            <author initials="J." surname="Hardwick" fullname="Jonathan Hardwick">
              <organization showOnFrontPage="true">Microsoft</organization>
            </author>
            <author initials="J." surname="Tantsura" fullname="Jeff Tantsura">
              <organization showOnFrontPage="true">Nvidia</organization>
            </author>
            <date month="May" day="21" year="2024"/>
          </front>
          <seriesInfo name="Internet-Draft" value="draft-ietf-pce-pcep-yang-25"/>
          <refcontent>Work in Progress</refcontent>
        </reference>
        <reference anchor="RFC4655" target="https://www.rfc-editor.org/info/rfc4655" quoteTitle="true" derivedAnchor="RFC4655">
          <front>
            <title>A Path Computation Element (PCE)-Based Architecture</title>
            <author fullname="A. Farrel" initials="A." surname="Farrel"/>
            <author fullname="J.-P. Vasseur" initials="J.-P." surname="Vasseur"/>
            <author fullname="J. Ash" initials="J." surname="Ash"/>
            <date month="August" year="2006"/>
            <abstract>
              <t indent="0">Constraint-based path computation is a fundamental building block for traffic engineering systems such as Multiprotocol Label Switching (MPLS) and Generalized Multiprotocol Label Switching (GMPLS) networks. Path computation in large, multi-domain, multi-region, or multi-layer networks is complex and may require special computational components and cooperation between the different network domains.</t>
              <t indent="0">This document specifies the architecture for a Path Computation Element (PCE)-based model to address this problem space. This document does not attempt to provide a detailed description of all the architectural components, but rather it describes a set of building blocks for the PCE architecture from which solutions may be constructed. This memo provides information for the Internet community.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="4655"/>
          <seriesInfo name="DOI" value="10.17487/RFC4655"/>
        </reference>
        <reference anchor="RFC8283" target="https://www.rfc-editor.org/info/rfc8283" quoteTitle="true" derivedAnchor="RFC8283">
          <front>
            <title>An Architecture for Use of PCE and the PCE Communication Protocol (PCEP) in a Network with Central Control</title>
            <author fullname="A. Farrel" initials="A." role="editor" surname="Farrel"/>
            <author fullname="Q. Zhao" initials="Q." role="editor" surname="Zhao"/>
            <author fullname="Z. Li" initials="Z." surname="Li"/>
            <author fullname="C. Zhou" initials="C." surname="Zhou"/>
            <date month="December" year="2017"/>
            <abstract>
              <t indent="0">The Path Computation Element (PCE) is a core component of Software- Defined Networking (SDN) systems. It can compute optimal paths for traffic across a network and can also update the paths to reflect changes in the network or traffic demands.</t>
              <t indent="0">PCE was developed to derive paths for MPLS Label Switched Paths (LSPs), which are supplied to the head end of the LSP using the Path Computation Element Communication Protocol (PCEP).</t>
              <t indent="0">SDN has a broader applicability than signaled MPLS traffic-engineered (TE) networks, and the PCE may be used to determine paths in a range of use cases including static LSPs, segment routing, Service Function Chaining (SFC), and most forms of a routed or switched network. It is, therefore, reasonable to consider PCEP as a control protocol for use in these environments to allow the PCE to be fully enabled as a central controller.</t>
              <t indent="0">This document briefly introduces the architecture for PCE as a central controller, examines the motivations and applicability for PCEP as a control protocol in this environment, and introduces the implications for the protocol. A PCE-based central controller can simplify the processing of a distributed control plane by blending it with elements of SDN and without necessarily completely replacing it.</t>
              <t indent="0">This document does not describe use cases in detail and does not define protocol extensions: that work is left for other documents.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8283"/>
          <seriesInfo name="DOI" value="10.17487/RFC8283"/>
        </reference>
        <reference anchor="RFC8754" target="https://www.rfc-editor.org/info/rfc8754" quoteTitle="true" derivedAnchor="RFC8754">
          <front>
            <title>IPv6 Segment Routing Header (SRH)</title>
            <author fullname="C. Filsfils" initials="C." role="editor" surname="Filsfils"/>
            <author fullname="D. Dukes" initials="D." role="editor" surname="Dukes"/>
            <author fullname="S. Previdi" initials="S." surname="Previdi"/>
            <author fullname="J. Leddy" initials="J." surname="Leddy"/>
            <author fullname="S. Matsushima" initials="S." surname="Matsushima"/>
            <author fullname="D. Voyer" initials="D." surname="Voyer"/>
            <date month="March" year="2020"/>
            <abstract>
              <t indent="0">Segment Routing can be applied to the IPv6 data plane using a new type of Routing Extension Header called the Segment Routing Header (SRH). This document describes the SRH and how it is used by nodes that are Segment Routing (SR) capable.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8754"/>
          <seriesInfo name="DOI" value="10.17487/RFC8754"/>
        </reference>
        <reference anchor="RFC9256" target="https://www.rfc-editor.org/info/rfc9256" quoteTitle="true" derivedAnchor="RFC9256">
          <front>
            <title>Segment Routing Policy Architecture</title>
            <author fullname="C. Filsfils" initials="C." surname="Filsfils"/>
            <author fullname="K. Talaulikar" initials="K." role="editor" surname="Talaulikar"/>
            <author fullname="D. Voyer" initials="D." surname="Voyer"/>
            <author fullname="A. Bogdanov" initials="A." surname="Bogdanov"/>
            <author fullname="P. Mattes" initials="P." surname="Mattes"/>
            <date month="July" year="2022"/>
            <abstract>
              <t indent="0">Segment Routing (SR) allows a node to steer a packet flow along any path. Intermediate per-path states are eliminated thanks to source routing. SR Policy is an ordered list of segments (i.e., instructions) that represent a source-routed policy. Packet flows are steered into an SR Policy on a node where it is instantiated called a headend node. The packets steered into an SR Policy carry an ordered list of segments associated with that SR Policy.</t>
              <t indent="0">This document updates RFC 8402 as it details the concepts of SR Policy and steering into an SR Policy.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="9256"/>
          <seriesInfo name="DOI" value="10.17487/RFC9256"/>
        </reference>
      </references>
    </references>
    <section anchor="Acknowledgement" numbered="false" toc="include" removeInRFC="false" pn="section-appendix.a">
      <name slugifiedName="name-acknowledgements">Acknowledgements</name>
      <t indent="0" pn="section-appendix.a-1">We would like to thank <contact fullname="Milos Fabian"/>, <contact fullname="Mrinmoy Das"/>, <contact fullname="Andrew Stone"/>, <contact fullname="Tom Petch"/>, <contact fullname="Aijun Wang"/>, <contact fullname="Olivier Dugeon"/>, and <contact fullname="Adrian Farrel"/> for
      their valuable comments.</t>
      <t indent="0" pn="section-appendix.a-2">Thanks to <contact fullname="Julien Meuric"/> for shepherding. Thanks
      to <contact fullname="John Scudder"/> for the AD review.</t>
      <t indent="0" pn="section-appendix.a-3">Thanks to <contact fullname="Theresa Enghardt"/> for the GENART review.</t>
      <t indent="0" pn="section-appendix.a-4">Thanks to <contact fullname="Martin Vigoureux"/>, <contact fullname="Benjamin Kaduk"/>, <contact fullname="Éric Vyncke"/>, <contact fullname="Lars Eggert"/>, <contact fullname="Murray Kucherawy"/>, and
      <contact fullname="Erik Kline"/> for the IESG reviews.</t>
    </section>
    <section toc="include" numbered="false" removeInRFC="false" pn="section-appendix.b">
      <name slugifiedName="name-contributors">Contributors</name>
      <contact fullname="Jonathan Hardwick">
        <organization showOnFrontPage="true">Microsoft</organization>
        <address>
          <postal>
            <country>United Kingdom</country>
          </postal>
          <email>jonhardwick@microsoft.com</email>
        </address>
      </contact>
      <contact fullname="Dhruv Dhody">
        <organization showOnFrontPage="true">Huawei Technologies</organization>
        <address>
          <postal>
            <street>Divyashree Techno Park, Whitefield</street>
            <city>Bangalore</city>
            <region>Karnataka</region>
            <country>India</country>
            <code>560066</code>
          </postal>
          <email>dhruv.ietf@gmail.com</email>
        </address>
      </contact>
      <contact fullname="Mahendra Singh Negi">
        <organization showOnFrontPage="true">RtBrick India</organization>
        <address>
          <postal>
            <street>N-17L, Floor-1, 18th Cross Rd, HSR Layout Sector-3</street>
            <city>Bangalore</city>
            <region>Karnataka</region>
            <country>India</country>
            <code>560102</code>
          </postal>
          <email>mahend.ietf@gmail.com</email>
        </address>
      </contact>
      <contact fullname="Mike Koldychev">
        <organization showOnFrontPage="true">Cisco Systems, Inc.</organization>
        <address>
          <postal>
            <street>2000 Innovation Drive</street>
            <city>Kanata</city>
            <region>Ontario</region>
            <code>K2K 3E8</code>
            <country>Canada</country>
          </postal>
          <email>mkoldych@cisco.com</email>
        </address>
      </contact>
      <contact fullname="Zafar Ali">
        <organization showOnFrontPage="true">Cisco Systems, Inc.</organization>
        <address>
          <email>zali@cisco.com</email>
        </address>
      </contact>
    </section>
    <section anchor="authors-addresses" numbered="false" removeInRFC="false" toc="include" pn="section-appendix.c">
      <name slugifiedName="name-authors-addresses">Authors' Addresses</name>
      <author fullname="Siva Sivabalan" initials="S." surname="Sivabalan">
        <organization showOnFrontPage="true">Ciena Corporation</organization>
        <address>
          <email>msiva282@gmail.com</email>
        </address>
      </author>
      <author fullname="Clarence Filsfils" initials="C." surname="Filsfils">
        <organization showOnFrontPage="true">Cisco Systems, Inc.</organization>
        <address>
          <postal>
            <extaddr>Pegasus Parc</extaddr>
            <street>De Kleetlaan 6a</street>
            <city>Brabant</city>
            <code>1831</code>
            <country>Belgium</country>
          </postal>
          <email>cfilsfil@cisco.com</email>
        </address>
      </author>
      <author fullname="Jeff Tantsura" initials="J." surname="Tantsura">
        <organization showOnFrontPage="true">Nvidia</organization>
        <address>
          <email>jefftant.ietf@gmail.com</email>
        </address>
      </author>
      <author fullname="Stefano Previdi" initials="S." surname="Previdi">
        <organization showOnFrontPage="true">Huawei Technologies</organization>
        <address>
          <email>stefano@previdi.net</email>
        </address>
      </author>
      <author fullname="Cheng Li" initials="C." role="editor">
        <organization showOnFrontPage="true">Huawei Technologies</organization>
        <address>
          <postal>
            <street>Huawei Campus, No. 156 Beiqing Rd.</street>
            <city>Beijing</city>
            <code>100095</code>
            <country>China</country>
          </postal>
          <email>c.l@huawei.com</email>
        </address>
      </author>
    </section>
  </back>
</rfc>
