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<rfc xmlns:xi="http://www.w3.org/2001/XInclude" version="3"
submissionType="IETF" category="std" consensus="true"
docName="draft-ietf-lsr-rfc8920bis-06" indexInclude="true" number="9492" ipr="trust200902"
updates="" obsoletes="8920" scripts="Common,Latin" sortRefs="true" submissionType="IETF" symRefs="true" tocDepth="3"
tocInclude="true" xml:lang="en">

  <link href="https://datatracker.ietf.org/doc/draft-ietf-ospf-te-link-attr-reuse-16" rel="prev"/>
  <link href="https://dx.doi.org/10.17487/rfc8920" rel="alternate"/>
  <link href="urn:issn:2070-1721" rel="alternate"/>

  <front>
    <title abbrev="OSPF App-Specific Link Attributes">OSPF
    Application-Specific Link Attributes</title>
    <seriesInfo name="Internet-Draft" value="draft-ietf-lsr-rfc8920bis-06" stream="IETF"/> name="RFC" value="9492"/>
    <author fullname="Peter Psenak" initials="P." role="editor" surname="Psenak">
      <organization showOnFrontPage="true">Cisco
      <organization>Cisco Systems</organization>
      <address>
        <postal>
          <street/>
          <city/>
          <region/>
          <code/>
          <country>Slovakia</country>
        </postal>
        <email>ppsenak@cisco.com</email>
      </address>
    </author>
    <author initials="L." surname="Ginsberg" fullname="Les Ginsberg">
      <organization showOnFrontPage="true">Cisco
      <organization>Cisco Systems</organization>
      <address>
	<postal>
          <street/>
          <city/>
          <region/>
          <code/>
          <country>United States of America</country>
        </postal>
        <email>ginsberg@cisco.com</email>
      </address>
    </author>
    <author initials="W." surname="Henderickx" fullname="Wim Henderickx">
      <organization showOnFrontPage="true">Nokia</organization>
      <organization>Nokia</organization>
      <address>
        <postal>
          <street>Copernicuslaan 50</street>
          <city>Antwerp</city>
          <country>Belgium</country>
          <code>2018 94089</code>
        </postal>
        <email>wim.henderickx@nokia.com</email>
      </address>
    </author>
    <author fullname="Jeff Tantsura" initials="J." surname="Tantsura">
      <organization showOnFrontPage="true">Nvidia</organization>
      <organization>Nvidia</organization>
      <address>
        <postal>
          <street/>
          <city/>
          <region/>
          <code/>
          <country>United States of America</country>
        </postal>
        <email>jefftant.ietf@gmail.com</email>
      </address>
    </author>
    <author fullname="John Drake" initials="J." surname="Drake">
      <organization showOnFrontPage="true">Juniper
      <organization>Juniper Networks</organization>
      <address>
        <postal>
          <street/>
          <city/>
          <region/>
          <code/>
          <country>United States of America</country>
        </postal>
        <email>jdrake@juniper.net</email>
      </address>
    </author>
    <date year="2023"/>
    <area>Routing</area>
    <workgroup>LSR Working Group</workgroup>
    <abstract pn="section-abstract">
      <t indent="0" pn="section-abstract-1">Existing year="2023" month="October"/>
    <area>rtg</area>
    <workgroup>lsr</workgroup>

    <abstract>
      <t>Existing traffic-engineering-related link attribute advertisements
    have been defined and are used in RSVP-TE deployments.
Since the
    original RSVP-TE use case was defined, additional applications (e.g., such as
    Segment Routing (SR) Policy and Loop-Free Alternates) Alternates (LFAs) that also make use of the
    link attribute advertisements have been defined.  In
    cases where multiple applications wish to make use of these link
    attributes, the current advertisements do not support application-specific values for a given attribute, nor do they support indication
    of which applications are using the advertised value for a given
    link.  This document introduces new link attribute advertisements in OSPFv2
       and OSPFv3 that address both of these shortcomings.</t>
      <t indent="0" pn="section-abstract-2">This
      <t>This document obsoletes RFC 8920.</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/rfc8920" 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) 2020 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 Simplified BSD License text as described in
            Section 4.e of the Trust Legal Provisions and are provided without
            warranty as described in the Simplified BSD License.
        </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-requirements-language">Requirements Language</xref></t>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.2">
            <t indent="0" keepWithNext="true" 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-discussion">Requirements Discussion</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-existing-advertisement-of-l">Existing Advertisement of Link Attributes</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-advertisement-of-link-attri">Advertisement of Link Attributes</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-ospfv2-extended-link-opaque">OSPFv2 Extended Link Opaque LSA and OSPFv3 E-Router-LSA</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-advertisement-of-applicatio">Advertisement of Application-Specific Values</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-reused-te-link-attributes">Reused TE Link Attributes</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.6.2">
              <li pn="section-toc.1-1.6.2.1">
                <t indent="0" pn="section-toc.1-1.6.2.1.1"><xref derivedContent="6.1" format="counter" sectionFormat="of" target="section-6.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-shared-risk-link-group-srlg">Shared Risk Link Group (SRLG)</xref></t>
              </li>
              <li pn="section-toc.1-1.6.2.2">
                <t indent="0" pn="section-toc.1-1.6.2.2.1"><xref derivedContent="6.2" format="counter" sectionFormat="of" target="section-6.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-extended-metrics">Extended Metrics</xref></t>
              </li>
              <li pn="section-toc.1-1.6.2.3">
                <t indent="0" pn="section-toc.1-1.6.2.3.1"><xref derivedContent="6.3" format="counter" sectionFormat="of" target="section-6.3"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-administrative-group">Administrative Group</xref></t>
              </li>
              <li pn="section-toc.1-1.6.2.4">
                <t indent="0" pn="section-toc.1-1.6.2.4.1"><xref derivedContent="6.4" format="counter" sectionFormat="of" target="section-6.4"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-traffic-engineering-metric">Traffic Engineering Metric</xref></t>
              </li>
            </ul>
          </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-maximum-link-bandwidth">Maximum Link Bandwidth</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-considerations-for-extended">Considerations for Extended TE Metrics</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-local-interface-ipv6-addres">Local Interface IPv6 Address Sub-TLV</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-remote-interface-ipv6-addre">Remote Interface IPv6 Address Sub-TLV</xref></t>
          </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-attribute-advertisements-an">Attribute Advertisements and Enablement</xref></t>
          </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-deployment-considerations">Deployment Considerations</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.12.2">
              <li pn="section-toc.1-1.12.3.1">
                <t indent="0" pn="section-toc.1-1.12.3.1.1"><xref derivedContent="12.1" format="counter" sectionFormat="of" target="section-12.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-use-of-legacy-rsvp-te-lsa-a">Use of Legacy RSVP-TE LSA Advertisements</xref></t>
              </li>
              <li pn="section-toc.1-1.12.3.2">
                <t indent="0" pn="section-toc.1-1.12.3.2.1"><xref derivedContent="12.2" format="counter" sectionFormat="of" target="section-12.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-interoperability-backwards-">Interoperability, Backwards Compatibility, and Migration Concerns</xref></t>
                <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.12.3.2.2">
                  <li pn="section-toc.1-1.12.3.2.2.1">
                    <t indent="0" pn="section-toc.1-1.12.3.2.2.1.1"><xref derivedContent="12.3.1" format="counter" sectionFormat="of" target="section-12.3.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-multiple-applications-commo">Multiple Applications: Common Attributes with  RSVP-TE</xref></t>
                  </li>
                  <li pn="section-toc.1-1.12.3.2.2.2">
                    <t indent="0" pn="section-toc.1-1.12.2.3.2.2.1"><xref derivedContent="12.3.2" format="counter" sectionFormat="of" target="section-12.3.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-multiple-applications-some-">Multiple Applications: Some Attributes Not Shared with RSVP-TE</xref></t>
                  </li>
                  <li pn="section-toc.1-1.12.3.2.2.3">
                    <t indent="0" pn="section-toc.1-1.12.3.2.2.3.1"><xref derivedContent="12.3.3" format="counter" sectionFormat="of" target="section-12.3.3"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-interoperability-with-legac">Interoperability with Legacy Routers</xref></t>
                  </li>
                  <li pn="section-toc.1-1.12.3.2.2.4">
                    <t indent="0" pn="section-toc.1-1.12.3.2.2.4.1"><xref derivedContent="12.3.4" format="counter" sectionFormat="of" target="section-12.3.4"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-use-of-application-specific">Use of Application-Specific Advertisements for RSVP-TE</xref></t>
                  </li>
                </ul>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.13">
            <t indent="0" pn="section-toc.1-1.13.1"><xref derivedContent="13" format="counter" sectionFormat="of" target="section-13"/>. <xref derivedContent="" format="title" sectionFormat="of" target="name-security-considerations">Security Considerations</xref></t>
          </li>
          <li pn="section-toc.1-1.14">
            <t indent="0" pn="section-toc.1-1.14.1"><xref derivedContent="14" format="counter" sectionFormat="of" target="section-14"/>. <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.1-1.14.2">
              <li pn="section-toc.1-1.14.2.1">
                <t indent="0" pn="section-toc.1-1.14.2.1.1"><xref derivedContent="14.1" format="counter" sectionFormat="of" target="section-14.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-ospfv2">OSPFv2</xref></t>
              </li>
              <li pn="section-toc.1-1.14.2.2">
                <t indent="0" pn="section-toc.1-1.14.2.2.1"><xref derivedContent="14.2" format="counter" sectionFormat="of" target="section-14.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-ospfv3">OSPFv3</xref></t>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.15">
            <t indent="0" pn="section-toc.1-1.15.1"><xref derivedContent="15" format="counter" sectionFormat="of" target="section-16"/>. <xref derivedContent="" format="title" sectionFormat="of" target="name-references">References</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.15.2">
              <li pn="section-toc.1-1.15.2.1">
                <t indent="0" pn="section-toc.1-1.15.2.1.1"><xref derivedContent="15.1" format="counter" sectionFormat="of" target="section-16.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-normative-references">Normative References</xref></t>
              </li>
              <li pn="section-toc.1-1.15.2.2">
                <t indent="0" pn="section-toc.1-1.15.2.2.1"><xref derivedContent="15.2" format="counter" sectionFormat="of" target="section-16.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-informative-references">Informative References</xref></t>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.16">
            <t indent="0" pn="section-toc.1-1.16.1"><xref derivedContent="" format="none" sectionFormat="of" target="section-appendix.a"/><xref derivedContent="" format="title" sectionFormat="of" target="name-acknowledgments">Acknowledgments</xref></t>
          </li>
          <li pn="section-toc.1-1.17">
            <t indent="0" pn="section-toc.1-1.17.1"><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.1-1.18">
            <t indent="0" pn="section-toc.1-1.18.1"><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 numbered="true" toc="include" removeInRFC="false" pn="section-1">
      <name slugifiedName="name-introduction">Introduction</name>
      <t indent="0" pn="section-1-1"> NOTE: This document makes modest editorial
      changes to the content of RFC 8920 which it obsoletes. A detailed description
      of the changes is provided in <xref target="changes-to-rfc8920" format="default" sectionFormat="of" derivedContent="Section 15"/>. This note was added
      for the benefit of IESG reviewers and SHOULD be removed by the RFC Editor
      prior to publication.</t>
      <t indent="0" pn="section-1-2">Advertisement
    <section>
      <name>Introduction</name>
      <t>Advertisement of link attributes by the OSPFv2 <xref target="RFC2328" format="default" sectionFormat="of" derivedContent="RFC2328"/> target="RFC2328"/> and OSPFv3 <xref target="RFC5340" format="default" sectionFormat="of" derivedContent="RFC5340"/> target="RFC5340"/> protocols in support of traffic engineering (TE) was
       introduced by <xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/> target="RFC3630"/> and <xref target="RFC5329" format="default" sectionFormat="of" derivedContent="RFC5329"/>, target="RFC5329"/>, respectively. It has been extended
       by <xref target="RFC4203" format="default" sectionFormat="of" derivedContent="RFC4203"/>, <xref target="RFC7308" format="default" sectionFormat="of" derivedContent="RFC7308"/>, target="RFC4203"/>, <xref target="RFC7308"/>, and <xref target="RFC7471" format="default" sectionFormat="of" derivedContent="RFC7471"/>. target="RFC7471"/>.  Use
       of these extensions has been associated with deployments supporting
       Traffic Engineering
       TE over Multiprotocol Label Switching (MPLS) in the
       presence of the Resource Reservation Protocol (RSVP), more succinctly
       referred to as RSVP-TE <xref target="RFC3209" format="default" sectionFormat="of" derivedContent="RFC3209"/>.</t>
      <t indent="0" pn="section-1-3">For target="RFC3209"/>.</t>
      <t>For the purposes of this document, an application is a technology
       that makes use of link attribute advertisements, examples of which are
       listed in <xref target="ADVAPPVAL" format="default" sectionFormat="of" derivedContent="Section 5"/>.</t>
      <t indent="0" pn="section-1-4">In target="ADVAPPVAL"/>.</t>
      <t>In recent years, new applications have been introduced that have use
       cases for many of the link attributes historically used by RSVP-TE.
       Such applications include Segment Routing (SR) SR Policy <xref target="RFC9256" format="default" sectionFormat="of" derivedContent="SEGMENT-ROUTING"/> target="RFC9256"/> and
       Loop-Free Alternates (LFAs)
       LFAs <xref target="RFC5286" format="default" sectionFormat="of" derivedContent="RFC5286"/>. target="RFC5286"/>. This has introduced ambiguity in that if a
       deployment includes a mix of RSVP-TE support and SR Policy support, for
       example, it is not possible to unambiguously indicate which
       advertisements are to be used by RSVP-TE and which advertisements are
       to be used by SR Policy.  If the topologies are fully congruent, this
       may not be an issue, but any incongruence leads to ambiguity.</t>
      <t indent="0" pn="section-1-5">An
      <t>An example of where this ambiguity causes a problem is a network
       where RSVP-TE is enabled only on a subset of its links. A link
       attribute is advertised for the purpose of another application (e.g.,
       SR Policy) for a link that is not enabled for RSVP-TE.  As soon as the
       router that is an RSVP-TE head end sees the link attribute being
       advertised for that link, it assumes RSVP-TE is enabled on that link,
       even though it is not.  If such an RSVP-TE head-end router tries to set
       up an RSVP-TE path via that link, it will result in the path a setup
       failure.</t>
      <t indent="0" pn="section-1-6">An failure for the path.</t>
      <t>An additional issue arises in cases where both applications are
       supported on a link but the link attribute values associated with each
       application differ.  Current advertisements do not support advertising
       application-specific values for the same attribute on a specific
       link.</t>
      <t indent="0" pn="section-1-7">This
      <t>This document defines extensions that address these issues.  Also,
    as evolution of use cases for link attributes can be expected to
    continue in the years to come, this document defines a solution that
    is easily extensible for the introduction of new applications and new
    use cases.</t>
      <section numbered="true" toc="include" removeInRFC="false" pn="section-1.1">
        <name slugifiedName="name-requirements-language">Requirements
      <section>
        <name>Requirements Language</name>
        <t indent="0" pn="section-1.1-1">The
        <t>
    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 BCP&nbsp;14 <xref target="RFC2119"/> <xref target="RFC2119" format="default" sectionFormat="of" derivedContent="RFC2119"/> <xref target="RFC8174" format="default" sectionFormat="of" derivedContent="RFC8174"/> target="RFC8174"/>
    when, and only when, they appear in all capitals, as shown here.</t> here.
        </t>
      </section>
    </section>
    <section anchor="REQDIS" numbered="true" toc="include" removeInRFC="false" pn="section-2">
      <name slugifiedName="name-requirements-discussion">Requirements anchor="REQDIS">
      <name>Requirements Discussion</name>
      <t indent="0" pn="section-2-1">As
      <t>As stated previously, evolution of use cases for link attributes can
       be expected to continue. Therefore, any discussion of existing use cases
       is limited to requirements that are known at the time of this writing.
       However, in order to determine the functionality required beyond what
       already exists in OSPF, it is only necessary to discuss use cases that
       justify the key points identified in the introduction, which are:</t>
      <ol spacing="normal" type="1" indent="adaptive" start="1" pn="section-2-2">
      <ol>
	 <li pn="section-2-2.1" derivedCounter="1.">Support for indicating which applications are using the link
	   attribute advertisements on a link</li> link.</li>
        <li pn="section-2-2.2" derivedCounter="2.">Support for advertising application-specific values for the same
	   attribute on a link</li> link.</li>
      </ol>
      <t indent="0" pn="section-2-3"><xref target="RFC7855" format="default" sectionFormat="of" derivedContent="RFC7855"/>
      <t><xref target="RFC7855"/> discusses use cases and requirements for Segment Routing
       (SR). SR.
       Included among these use cases is SR Policy, which is defined in
       <xref target="RFC9256" format="default" sectionFormat="of" derivedContent="SEGMENT-ROUTING"/>. target="RFC9256"/>. If both RSVP-TE
       and SR Policy are deployed in a network, link attribute advertisements
       can be used by one or both of these applications. There is no
       requirement for the link attributes advertised on a given link used by
       SR Policy to be identical to the link attributes advertised on that same
       link used by RSVP-TE; thus, there is a clear requirement to indicate
       independently which link attribute advertisements are to be used by each
       application.</t>
      <t indent="0" pn="section-2-4">As
      <t>As the number of applications that may wish to utilize link
       attributes may grow in the future, an additional requirement is that the
       extensions defined allow the association of additional applications to
       link attributes without altering the format of the advertisements or
      introducing new backwards-compatibility issues.</t>
      <t indent="0" pn="section-2-5">Finally,
      <t>Finally, there may still be many cases where a single attribute value
       can be shared among multiple applications, so the solution must minimize
       advertising duplicate link/attribute pairs whenever possible.</t>
    </section>
    <section anchor="LEG_ADV" numbered="true" toc="include" removeInRFC="false" pn="section-3">
      <name slugifiedName="name-existing-advertisement-of-l">Existing anchor="LEG_ADV">
      <name>Existing Advertisement of Link Attributes</name>
      <t indent="0" pn="section-3-1">There
      <t>There are existing advertisements used in support of RSVP-TE.  These
       advertisements are carried in the OSPFv2 TE Opaque Link State
       Advertisement (LSA) <xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/> target="RFC3630"/> and
       OSPFv3 Intra-Area-TE-LSA <xref target="RFC5329" format="default" sectionFormat="of" derivedContent="RFC5329"/>. target="RFC5329"/>. Additional RSVP-TE link attributes have been
       defined by <xref target="RFC4203" format="default" sectionFormat="of" derivedContent="RFC4203"/>, <xref target="RFC7308" format="default" sectionFormat="of" derivedContent="RFC7308"/>, and <xref target="RFC7471" format="default" sectionFormat="of" derivedContent="RFC7471"/>.</t>
      <t indent="0" pn="section-3-2">Extended target="RFC4203"/>, <xref target="RFC7308"/>, and <xref target="RFC7471"/>.</t>
      <t>Extended Link Opaque LSAs as defined in <xref target="RFC7684" format="default" sectionFormat="of" derivedContent="RFC7684"/> target="RFC7684"/> for OSPFv2 and
  E-Router-LSAs <xref target="RFC8362" format="default" sectionFormat="of" derivedContent="RFC8362"/> target="RFC8362"/> for OSPFv3 are used to advertise link
  attributes that are used by applications other than RSVP-TE or GMPLS <xref target="RFC4203" format="default" sectionFormat="of" derivedContent="RFC4203"/>. target="RFC4203"/>.
  These LSAs were defined as generic containers for distribution of the extended link attributes.</t>
    </section>
    <section numbered="true" toc="include" removeInRFC="false" pn="section-4">
      <name slugifiedName="name-advertisement-of-link-attri">Advertisement
    <section>
      <name>Advertisement of Link Attributes</name>
      <t indent="0" pn="section-4-1">This
      <t>This section outlines the solution for advertising link attributes
   originally defined for RSVP-TE or GMPLS when they are used for other applications.</t>
      <section numbered="true" toc="include" removeInRFC="false" pn="section-4.1">
        <name slugifiedName="name-ospfv2-extended-link-opaque">OSPFv2
      <section>
        <name>OSPFv2 Extended Link Opaque LSA and OSPFv3 E-Router-LSA</name>
        <t indent="0" pn="section-4.1-1">The
        <t>The following are the advantages of Extended Link Opaque LSAs as defined in <xref target="RFC7684" format="default" sectionFormat="of" derivedContent="RFC7684"/> target="RFC7684"/>
   for OSPFv2 and E-Router-LSAs <xref target="RFC8362" format="default" sectionFormat="of" derivedContent="RFC8362"/> target="RFC8362"/> for OSPFv3 with respect
   to the advertisement of link attributes originally defined for RSVP-TE when used in packet
   networks and in GMPLS:
        </t>
        <ol spacing="normal" type="1" indent="adaptive" start="1" pn="section-4.1-2">
        <ol>
	   <li pn="section-4.1-2.1" derivedCounter="1.">Advertisement of the link attributes does not make the link part of the RSVP-TE topology.
      It avoids any conflicts and is fully compatible with <xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/> target="RFC3630"/> and
      <xref target="RFC5329" format="default" sectionFormat="of" derivedContent="RFC5329"/>.</li> target="RFC5329"/>.</li>
          <li pn="section-4.1-2.2" derivedCounter="2.">The OSPFv2 TE Opaque LSA and OSPFv3 Intra-Area-TE-LSA remain
	   truly opaque to OSPFv2 and OSPFv3 as originally defined in <xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/> target="RFC3630"/> and <xref target="RFC5329" format="default" sectionFormat="of" derivedContent="RFC5329"/>, target="RFC5329"/>, respectively. Their contents are not inspected
	   by OSPF, which instead acts as a pure transport.</li>
          <li pn="section-4.1-2.3" derivedCounter="3.">There is a clear distinction between link attributes used by RSVP-TE and
	link attributes used by other OSPFv2 or OSPFv3 applications.</li>
          <li pn="section-4.1-2.4" derivedCounter="4.">All link attributes that are used by other applications are advertised in the Extended Link Opaque LSA in OSPFv2 <xref target="RFC7684" format="default" sectionFormat="of" derivedContent="RFC7684"/> target="RFC7684"/> or the OSPFv3
	E-Router-LSA <xref target="RFC8362" format="default" sectionFormat="of" derivedContent="RFC8362"/> target="RFC8362"/> in OSPFv3.</li>
        </ol>
        <t indent="0" pn="section-4.1-3">The
        <t>The disadvantage of this approach is that in rare cases, the same link attribute is
    advertised in both the TE Opaque and Extended Link Attribute LSAs in OSPFv2 or
    the Intra-Area-TE-LSA and E-Router-LSA in OSPFv3.</t>
        <t indent="0" pn="section-4.1-4">The
        <t>The Extended Link Opaque LSA <xref target="RFC7684" format="default" sectionFormat="of" derivedContent="RFC7684"/> target="RFC7684"/> and E-Router-LSA
   <xref target="RFC8362" format="default" sectionFormat="of" derivedContent="RFC8362"/> target="RFC8362"/> are used to advertise any link attributes used
   for non-RSVP-TE applications in OSPFv2 or OSPFv3, respectively, including those that have
   been originally defined for RSVP-TE applications (see <xref target="REUSED_ATTR" format="default" sectionFormat="of" derivedContent="Section 6"/>).</t>
        <t indent="0" pn="section-4.1-5">TE target="REUSED_ATTR"/>).</t>
        <t>TE link attributes used for RSVP-TE/GMPLS continue to use the OSPFv2 TE Opaque LSA
   <xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/> target="RFC3630"/> and OSPFv3 Intra-Area-TE-LSA <xref target="RFC5329" format="default" sectionFormat="of" derivedContent="RFC5329"/>.</t>
        <t indent="0" pn="section-4.1-6">The target="RFC5329"/>.</t>
        <t>The format of the link attribute TLVs that have been defined for
	 RSVP-TE applications will be kept unchanged even when they are used
	 for non-RSVP-TE applications. Unique codepoints are allocated for
	 these link attribute TLVs from the "OSPFv2 Extended Link TLV Sub-TLVs"
	 registry <xref target="RFC7684" format="default" sectionFormat="of" derivedContent="RFC7684"/> target="RFC7684"/> and from the
	 "OSPFv3 Extended-LSA Sub-TLVs" registry <xref target="RFC8362" format="default" sectionFormat="of" derivedContent="RFC8362"/>, target="RFC8362"/>, as specified in <xref target="IANA" format="default" sectionFormat="of" derivedContent="Section 14"/>.</t> target="IANA"/>.</t>
      </section>
    </section>
    <section anchor="ADVAPPVAL" numbered="true" toc="include" removeInRFC="false" pn="section-5">
      <name slugifiedName="name-advertisement-of-applicatio">Advertisement anchor="ADVAPPVAL">
      <name>Advertisement of Application-Specific Values</name>
      <t indent="0" pn="section-5-1">To
      <t>To allow advertisement of the application-specific values of the link
      attribute, a new an Application-Specific Link Attributes (ASLA) sub-TLV is
      defined.  The ASLA sub-TLV is a sub-TLV of the OSPFv2 Extended Link TLV
      <xref target="RFC7684" format="default" sectionFormat="of" derivedContent="RFC7684"/> target="RFC7684"/> and OSPFv3 Router-Link TLV <xref target="RFC8362" format="default" sectionFormat="of" derivedContent="RFC8362"/>.</t>
      <t indent="0" pn="section-5-2">In
      target="RFC8362"/>.</t>
      <t>In addition to advertising the link attributes for standardized
   applications, link attributes can be advertised for the purpose of
   applications that are not standardized.  We call such an
   application a "user-defined application" or "UDA".  These applications are
   not subject to standardization and are outside of the scope
   of this specification.</t>
      <t indent="0" pn="section-5-3">The
      <t>The ASLA sub-TLV is an optional sub-TLV of the OSPFv2 Extended Link TLV and
OSPFv3 Router-Link TLV. Multiple ASLA sub-TLVs can be present in a parent
TLV when different applications want to control different link attributes or
when a different value
of the same attribute needs to be advertised by multiple applications. The ASLA sub-TLV
<bcp14>MUST</bcp14> be used for advertisement of the link attributes listed at the end of this section
if these are advertised inside the OSPFv2 Extended Link TLV and OSPFv3 Router-Link TLV.
It has the following format:
</t>
      <artwork name="" type="" align="left" alt="" pn="section-5-4"> alt="">
 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             |             Length            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  SABM Length  |  UDABM Length |            Reserved           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|       Standard Application Identifier Bit Mask(SABM) Mask (SABM)         |
+-                                                             -+
|                            ...                                |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|       User-Defined Application Identifier Bit Mask(UDABM) Mask (UDABM)    |
+-                                                             -+
|                            ...                                |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                      Link Attribute sub-sub-TLVs sub-TLVs                  |
+-                                                             -+
|                            ...                                |
</artwork>
      <t indent="0" pn="section-5-5">
      <t> where:</t>
      <dl newline="false" indent="3" spacing="normal" pn="section-5-6">
        <dt pn="section-5-6.1">Type:</dt>
        <dd pn="section-5-6.2"> 10
      <dl>
        <dt>Type:</dt>
        <dd>10 (OSPFv2), 11 (OSPFv3)</dd>
        <dt pn="section-5-6.3">Length:</dt>
        <dd pn="section-5-6.4"> Variable</dd>
        <dt pn="section-5-6.5">SABM
        <dt>Length:</dt>
        <dd>Variable</dd>
        <dt>SABM Length:</dt>
        <dd pn="section-5-6.6"> Standard
        <dd>Standard Application Identifier Bit Mask Length in octets.
            The value <bcp14>MUST</bcp14> be 0, 4, or 8.
            If the Standard Application Identifier Bit Mask is not present, the SABM
            Length <bcp14>MUST</bcp14> be set to 0.</dd>
        <dt pn="section-5-6.7">UDABM
        <dt>UDABM Length:</dt>
        <dd pn="section-5-6.8"> User-Defined
        <dd>User-Defined Application Identifier Bit Mask Length in octets.
            The value <bcp14>MUST</bcp14> be 0, 4, or 8.
            If the User-Defined Application Identifier Bit Mask is not present, the
            UDABM Length <bcp14>MUST</bcp14> be set to 0.</dd>
        <dt pn="section-5-6.9">Standard
        <dt>Standard Application Identifier Bit Mask:</dt>
        <dd pn="section-5-6.10">
          <t indent="0" pn="section-5-6.10.1">Optional
        <dd>
          <t>Optional
          set of bits, where each bit represents a single standard
          application. Bits are defined in the "Link Attribute Applications" Application Identifiers"
          registry, which is defined in <xref target="RFC8919" format="default" sectionFormat="of" derivedContent="RFC8919"/>. target="RFC9479"/>.  Current assignments are repeated here for
          informational purposes:</t>
<artwork name="" align="center" type="" align="left" alt="" pn="section-5-6.10.2"> alt="">
 0 1 2 3 4 5 6 7 ...
+-+-+-+-+-+-+-+-+...
|R|S|F|          ...
+-+-+-+-+-+-+-+-+...
</artwork>
          <dl newline="false" spacing="normal" indent="3" pn="section-5-6.10.3">
            <dt pn="section-5-6.10.3.1">Bit
          <dl>
            <dt>Bit 0 (R-bit):</dt>
            <dd pn="section-5-6.10.3.2"> RSVP-TE.</dd>
            <dt pn="section-5-6.10.3.3">Bit
            <dd>RSVP-TE.</dd>
            <dt>Bit 1 (S-bit):</dt>
            <dd pn="section-5-6.10.3.4"> Segment Routing Policy.
            <dd>SR Policy (this is dataplane data plane independent).</dd>
            <dt pn="section-5-6.10.3.5">Bit
            <dt>Bit 2 (F-bit):</dt>
            <dd pn="section-5-6.10.3.6"> Loop-Free
            <dd>Loop-Free Alternate (LFA). Includes (includes all LFA types.</dd>
     types).</dd>
          </dl>
        </dd>
        <dt pn="section-5-6.11">User-Defined
        <dt>User-Defined Application Identifier Bit Mask:</dt>
        <dd pn="section-5-6.12"> Optional
        <dd>Optional set of bits, where each bit
        represents a single user-defined application.</dd>
      </dl>
      <t indent="0" pn="section-5-7">If
      <t>If the SABM or UDABM Length is other than 0, 4, or 8, the ASLA sub-TLV <bcp14>MUST</bcp14> be ignored
by the receiver.</t>
      <t indent="0" pn="section-5-8">Standard
      <t>Standard Application Identifier Bits are defined and sent starting with
   bit 0.  Undefined bits that are transmitted <bcp14>MUST</bcp14> be transmitted as 0 and <bcp14>MUST</bcp14> be ignored
   on receipt.  Bits that are not transmitted <bcp14>MUST</bcp14> be treated as if they
   are set to 0 on receipt.  Bits that are not supported by an
   implementation <bcp14>MUST</bcp14> be ignored on receipt.</t>
      <t indent="0" pn="section-5-9">User-Defined
      <t>User-Defined Application Identifier Bits have no relationship to
   Standard Application Identifier Bits and are not managed by IANA or
   any other standards body.  It is recommended that these bits be used
   starting with bit 0 so as to minimize the number of octets required
   to advertise all UDAs. Undefined bits that are transmitted <bcp14>MUST</bcp14> be
   transmitted as 0 and <bcp14>MUST</bcp14> be ignored on receipt. Bits that are not
   transmitted <bcp14>MUST</bcp14> be treated as if they are set to 0 on receipt.  Bits that are not
   supported by an implementation <bcp14>MUST</bcp14> be ignored on receipt.</t>
      <t indent="0" pn="section-5-10">If
      <t>If the link attribute advertisement is intended to be only used by a specific set of applications,
corresponding bit masks <bcp14>MUST</bcp14> be present, present and one or more application-specific bit(s) bits <bcp14>MUST</bcp14> be set for all
applications that use the link attributes advertised in the ASLA sub-TLV.</t>
      <t indent="0" pn="section-5-11">Application
      <t>Application Identifier Bit Masks apply to all link attributes that support application-specific
values and are advertised in the ASLA sub-TLV.</t>
      <t indent="0" pn="section-5-12">The
      <t>The advantage of not making the Application Identifier Bit Masks part of the attribute advertisement
itself is that the format of any previously defined link attributes
can be kept and reused when advertising them in the ASLA sub-TLV.</t>
      <t indent="0" pn="section-5-13">If
      <t>If the same attribute is advertised in more than one ASLA sub-TLVs sub-TLV with the application
listed in the Application Identifier Bit Masks, the application <bcp14>SHOULD</bcp14> use the first instance of
advertisement and ignore any subsequent advertisements of that attribute.</t>
      <t indent="0" pn="section-5-14">Link
      <t>Link attributes MAY <bcp14>MAY</bcp14> be advertised associated with zero-length
      Application Identifier Bit Masks for both standard applications
      and user-defined applications. Such link attribute advertisements
      MUST
      <bcp14>MUST</bcp14> be used by standard applications and/or user defined user-defined applications
      when no link attribute advertisements with a non-zero-length
      Application Identifier Bit Mask and a matching Application Identifier
      Bit set are present. Otherwise, such link attribute
      advertisements MUST NOT <bcp14>MUST NOT</bcp14> be used.</t>
      <t indent="0" pn="section-5-15">This
      <t>This document defines the initial set of link attributes that <bcp14>MUST</bcp14> use the ASLA sub-TLV if
advertised in the OSPFv2 Extended Link TLV or in the OSPFv3 Router-Link TLV.
Documents that define new link attributes <bcp14>MUST</bcp14> state whether the new attributes support
application-specific values and, as such, are advertised in an ASLA sub-TLV. The standard
link attributes that are advertised in ASLA sub-TLVs are:

      </t>
      <ul bare="false" empty="false" indent="3" spacing="normal" pn="section-5-16">
        <li pn="section-5-16.1"> Shared
      <ul>
        <li>Shared Risk Link Group <xref target="RFC4203" format="default" sectionFormat="of" derivedContent="RFC4203"/></li>
        <li pn="section-5-16.2"> Unidirectional target="RFC4203"/></li>
        <li>Unidirectional Link Delay <xref target="RFC7471" format="default" sectionFormat="of" derivedContent="RFC7471"/></li>
        <li pn="section-5-16.3"> Min/Max target="RFC7471"/></li>
        <li>Min/Max Unidirectional Link Delay <xref target="RFC7471" format="default" sectionFormat="of" derivedContent="RFC7471"/></li>
        <li pn="section-5-16.4"> Unidirectional target="RFC7471"/></li>
        <li>Unidirectional Delay Variation <xref target="RFC7471" format="default" sectionFormat="of" derivedContent="RFC7471"/></li>
        <li pn="section-5-16.5"> Unidirectional target="RFC7471"/></li>
        <li>Unidirectional Link Loss <xref target="RFC7471" format="default" sectionFormat="of" derivedContent="RFC7471"/></li>
        <li pn="section-5-16.6"> Unidirectional target="RFC7471"/></li>
        <li>Unidirectional Residual Bandwidth <xref target="RFC7471" format="default" sectionFormat="of" derivedContent="RFC7471"/></li>
        <li pn="section-5-16.7"> Unidirectional target="RFC7471"/></li>
        <li>Unidirectional Available Bandwidth <xref target="RFC7471" format="default" sectionFormat="of" derivedContent="RFC7471"/></li>
        <li pn="section-5-16.8"> Unidirectional target="RFC7471"/></li>
        <li>Unidirectional Utilized Bandwidth <xref target="RFC7471" format="default" sectionFormat="of" derivedContent="RFC7471"/></li>
        <li pn="section-5-16.9"> Administrative target="RFC7471"/></li>
        <li>Administrative Group <xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/></li>
        <li pn="section-5-16.10"> Extended target="RFC3630"/></li>
        <li>Extended Administrative Group <xref target="RFC7308" format="default" sectionFormat="of" derivedContent="RFC7308"/></li>
        <li pn="section-5-16.11"> TE target="RFC7308"/></li>
        <li>TE Metric <xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/></li> target="RFC3630"/></li>
      </ul>
    </section>
    <section anchor="REUSED_ATTR" numbered="true" toc="include" removeInRFC="false" pn="section-6">
      <name slugifiedName="name-reused-te-link-attributes">Reused anchor="REUSED_ATTR">
      <name>Reused TE Link Attributes</name>
      <t indent="0" pn="section-6-1">This
      <t>This section defines the use case and indicates the codepoints (<xref target="IANA" format="default" sectionFormat="of" derivedContent="Section 14"/>) target="IANA"/>) from the "OSPFv2 Extended Link TLV
      Sub-TLVs" registry and "OSPFv3 Extended-LSA Sub-TLVs" registry for some of
      the link attributes that have been originally defined for RSVP-TE or
      GMPLS.</t>
      <section anchor="SRLG" numbered="true" toc="include" removeInRFC="false" pn="section-6.1">
        <name slugifiedName="name-shared-risk-link-group-srlg">Shared anchor="SRLG">
        <name>Shared Risk Link Group (SRLG)</name>
        <t indent="0" pn="section-6.1-1">The
<t>The SRLG of a link can be used in OSPF-calculated IPFRR (IP Fast Reroute)
   <xref target="RFC5714" format="default" sectionFormat="of" derivedContent="RFC5714"/> target="RFC5714"/> to compute a backup path
  that does not share any SRLG group with the protected link.</t>
        <t indent="0" pn="section-6.1-2">To
        <t>To advertise the SRLG of the link in the OSPFv2 Extended Link TLV, the same format
   for the sub-TLV defined in <xref target="RFC4203" sectionFormat="of" section="1.3" format="default" derivedLink="https://rfc-editor.org/rfc/rfc4203#section-1.3" derivedContent="RFC4203"/> section="1.3"/> is used with TLV
   type 11. Similarly, for OSPFv3 to advertise the SRLG in the OSPFv3 Router-Link
   TLV, TLV type 12 is used.</t>
      </section>
      <section numbered="true" toc="include" removeInRFC="false" pn="section-6.2">
        <name slugifiedName="name-extended-metrics">Extended
      <section>
        <name>Extended Metrics</name>
        <t indent="0" pn="section-6.2-1"><xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/>
        <t><xref target="RFC3630"/> defines several link bandwidth types. <xref target="RFC7471" format="default" sectionFormat="of" derivedContent="RFC7471"/> target="RFC7471"/>
  defines extended link metrics that are based on link bandwidth, delay, and loss
  characteristics. All of these can be used to compute primary and backup paths within an
  OSPF area to satisfy requirements for bandwidth, delay (nominal or worst case), or loss.</t>
        <t indent="0" pn="section-6.2-2">To
        <t>To advertise extended link metrics in the OSPFv2 Extended Link TLV, the same format
    for the sub-TLVs defined in <xref target="RFC7471" format="default" sectionFormat="of" derivedContent="RFC7471"/> target="RFC7471"/> is used with the following
    TLV types:
        </t>
        <dl indent="3" newline="false" spacing="normal" pn="section-6.2-3">
          <dt pn="section-6.2-3.1">12:</dt>
          <dd pn="section-6.2-3.2"> Unidirectional
        <dl>
          <dt>12:</dt>
          <dd>Unidirectional Link Delay</dd>
          <dt pn="section-6.2-3.3">13:</dt>
          <dd pn="section-6.2-3.4"> Min/Max
          <dt>13:</dt>
          <dd>Min/Max Unidirectional Link Delay</dd>
          <dt pn="section-6.2-3.5">14:</dt>
          <dd pn="section-6.2-3.6"> Unidirectional
          <dt>14:</dt>
          <dd>Unidirectional Delay Variation</dd>
          <dt pn="section-6.2-3.7">15:</dt>
          <dd pn="section-6.2-3.8"> Unidirectional
          <dt>15:</dt>
          <dd>Unidirectional Link Loss</dd>
          <dt pn="section-6.2-3.9">16:</dt>
          <dd pn="section-6.2-3.10"> Unidirectional
          <dt>16:</dt>
          <dd>Unidirectional Residual Bandwidth</dd>
          <dt pn="section-6.2-3.11">17:</dt>
          <dd pn="section-6.2-3.12"> Unidirectional
          <dt>17:</dt>
          <dd>Unidirectional Available Bandwidth</dd>
          <dt pn="section-6.2-3.13">18:</dt>
          <dd pn="section-6.2-3.14"> Unidirectional
          <dt>18:</dt>
          <dd>Unidirectional Utilized Bandwidth</dd>
        </dl>
        <t indent="0" pn="section-6.2-4">To
        <t>To advertise extended link metrics in the Router-Link TLV inside
	the OSPFv3 E-Router-LSA, the same format for the sub-TLVs defined in <xref target="RFC7471" format="default" sectionFormat="of" derivedContent="RFC7471"/> target="RFC7471"/> is used with the following
    TLV types:
        </t>
        <dl indent="3" newline="false" spacing="normal" pn="section-6.2-5">
          <dt pn="section-6.2-5.1">13:</dt>
          <dd pn="section-6.2-5.2"> Unidirectional
        <dl>
          <dt>13:</dt>
          <dd>Unidirectional Link Delay</dd>
          <dt pn="section-6.2-5.3">14:</dt>
          <dd pn="section-6.2-5.4"> Min/Max
          <dt>14:</dt>
          <dd>Min/Max Unidirectional Link Delay</dd>
          <dt pn="section-6.2-5.5">15:</dt>
          <dd pn="section-6.2-5.6"> Unidirectional
          <dt>15:</dt>
          <dd>Unidirectional Delay Variation</dd>
          <dt pn="section-6.2-5.7">16:</dt>
          <dd pn="section-6.2-5.8"> Unidirectional
          <dt>16:</dt>
          <dd>Unidirectional Link Loss</dd>
          <dt pn="section-6.2-5.9">17:</dt>
          <dd pn="section-6.2-5.10"> Unidirectional
          <dt>17:</dt>
          <dd>Unidirectional Residual Bandwidth</dd>
          <dt pn="section-6.2-5.11">18:</dt>
          <dd pn="section-6.2-5.12"> Unidirectional
          <dt>18:</dt>
          <dd>Unidirectional Available Bandwidth</dd>
          <dt pn="section-6.2-5.13">19:</dt>
          <dd pn="section-6.2-5.14"> Unidirectional
          <dt>19:</dt>
          <dd>Unidirectional Utilized Bandwidth</dd>
        </dl>
      </section>
      <section numbered="true" toc="include" removeInRFC="false" pn="section-6.3">
        <name slugifiedName="name-administrative-group">Administrative
      <section>
        <name>Administrative Group</name>
        <t indent="0" pn="section-6.3-1"><xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/>
        <t><xref target="RFC3630"/> and <xref target="RFC7308" format="default" sectionFormat="of" derivedContent="RFC7308"/> target="RFC7308"/> define the Administrative Group and
  Extended Administrative Group sub-TLVs, respectively.</t>
        <t indent="0" pn="section-6.3-2">To
        <t>To advertise the Administrative Group and Extended Administrative Group in the OSPFv2
    Extended Link TLV, the same format for the sub-TLVs defined in <xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/> target="RFC3630"/>
    and <xref target="RFC7308" format="default" sectionFormat="of" derivedContent="RFC7308"/> target="RFC7308"/> is used with the following TLV types:

        </t>
        <dl indent="3" newline="false" spacing="normal" pn="section-6.3-3">
          <dt pn="section-6.3-3.1">19:</dt>
          <dd pn="section-6.3-3.2">  Administrative
        <dl>
          <dt>19:</dt>
          <dd>Administrative Group</dd>
          <dt pn="section-6.3-3.3">20:</dt>
          <dd pn="section-6.3-3.4"> Extended
          <dt>20:</dt>
          <dd>Extended Administrative Group</dd>
        </dl>
        <t indent="0" pn="section-6.3-4">To
        <t>To advertise the Administrative Group and Extended Administrative Group in the OSPFv3
    Router-Link TLV, the same format for the sub-TLVs defined in <xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/> target="RFC3630"/>
    and <xref target="RFC7308" format="default" sectionFormat="of" derivedContent="RFC7308"/> target="RFC7308"/> is used with the following TLV types:

        </t>
        <dl indent="3" newline="false" spacing="normal" pn="section-6.3-5">
          <dt pn="section-6.3-5.1">20:</dt>
          <dd pn="section-6.3-5.2">  Administrative
        <dl>
          <dt>20:</dt>
          <dd>Administrative Group</dd>
          <dt pn="section-6.3-5.3">21:</dt>
          <dd pn="section-6.3-5.4"> Extended
          <dt>21:</dt>
          <dd>Extended Administrative Group</dd>
        </dl>
      </section>
      <section numbered="true" toc="include" removeInRFC="false" pn="section-6.4">
        <name slugifiedName="name-traffic-engineering-metric">Traffic Engineering
      <section>
        <name>TE Metric</name>
        <t indent="0" pn="section-6.4-1"><xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/>
        <t><xref target="RFC3630"/> defines the Traffic Engineering TE Metric.</t>
        <t indent="0" pn="section-6.4-2">To
        <t>To advertise the Traffic Engineering TE Metric in the OSPFv2 Extended Link TLV,
  the same format for the sub-TLV defined in <xref target="RFC3630" sectionFormat="of" section="2.5.5" format="default" derivedLink="https://rfc-editor.org/rfc/rfc3630#section-2.5.5" derivedContent="RFC3630"/> section="2.5.5"/>
  is used with TLV type 22. Similarly, for OSPFv3 to advertise the
  Traffic Engineering
  TE Metric in the OSPFv3 Router-Link TLV, TLV type 22 is used.</t>
      </section>
    </section>
    <section anchor="SPECIALMAXBANDW" numbered="true" toc="include" removeInRFC="false" pn="section-7">
      <name slugifiedName="name-maximum-link-bandwidth">Maximum anchor="SPECIALMAXBANDW">
      <name>Maximum Link Bandwidth</name>
      <t indent="0" pn="section-7-1">Maximum
      <t>Maximum link bandwidth is an application-independent attribute of the
  link that is defined in <xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/>. target="RFC3630"/>. Because
  it is an application-independent attribute, it <bcp14>MUST NOT</bcp14> be
  advertised in the ASLA sub-TLV.

Instead, it <bcp14>MAY</bcp14> be
  advertised as a sub-TLV of the Extended Link TLV in the Extended Link Opaque
  LSA in OSPFv2 <xref target="RFC7684" format="default" sectionFormat="of" derivedContent="RFC7684"/> target="RFC7684"/> or as a sub-TLV of
  the Router-Link TLV in the E-Router-LSA Router-Link TLV in OSPFv3
  <xref target="RFC8362" format="default" sectionFormat="of" derivedContent="RFC8362"/>.</t>
      <t indent="0" pn="section-7-2">To target="RFC8362"/>.</t>
      <t>To advertise the maximum link bandwidth in the OSPFv2 Extended Link TLV, the same
  format for the sub-TLV defined in <xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/> target="RFC3630"/> is used with
  TLV type 23.</t>
      <t indent="0" pn="section-7-3">To
      <t>To advertise the maximum link bandwidth in the OSPFv3 Router-Link TLV, the same
  format for the sub-TLV defined in <xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/> target="RFC3630"/> is used with
  TLV type 23.</t>
    </section>
    <section anchor="EXT_METRICS" numbered="true" toc="include" removeInRFC="false" pn="section-8">
      <name slugifiedName="name-considerations-for-extended">Considerations anchor="EXT_METRICS">
      <name>Considerations for Extended TE Metrics</name>
      <t indent="0" pn="section-8-1"><xref target="RFC7471" format="default" sectionFormat="of" derivedContent="RFC7471"/>
      <t><xref target="RFC7471"/> defines a number of dynamic performance metrics associated
   with a link.  It is conceivable that such metrics could be measured
   specific to traffic associated with a specific application.
   Therefore, this document includes support for advertising these link
   attributes specific to a given application.  However, in practice, it
   may well be more practical to have these metrics reflect the
   performance of all traffic on the link regardless of application.  In
   such cases, advertisements for these attributes can be associated
   with all of the applications utilizing that link. This can be done
   either by explicitly specifying the applications in the Application
   Identifier Bit Mask or by using a zero-length Application Identifier
   Bit Mask. The use of zero-length Application Identifier Bit Mask is
   further discussed in <xref target="ZLABM" format="default" sectionFormat="of" derivedContent="Section 12.2"/>.</t> target="ZLABM"/>.</t>
    </section>
    <section anchor="LOCALIPV6ADDR" numbered="true" toc="include" removeInRFC="false" pn="section-9">
      <name slugifiedName="name-local-interface-ipv6-addres">Local anchor="LOCALIPV6ADDR">
      <name>Local Interface IPv6 Address Sub-TLV</name>
      <t indent="0" pn="section-9-1">The
      <t>The Local Interface IPv6 Address sub-TLV is an application-independent attribute of the
  link that is defined in <xref target="RFC5329" format="default" sectionFormat="of" derivedContent="RFC5329"/>. target="RFC5329"/>. Because it is an application-independent attribute, it <bcp14>MUST NOT</bcp14> be advertised in the ASLA sub-TLV.  Instead, it <bcp14>MAY</bcp14> be
  advertised as a sub-TLV of the Router-Link TLV inside the OSPFv3 E-Router-LSA <xref target="RFC8362" format="default" sectionFormat="of" derivedContent="RFC8362"/>.</t>
      <t indent="0" pn="section-9-2">To target="RFC8362"/>.</t>
      <t>To advertise the Local Interface IPv6 Address sub-TLV in the OSPFv3 Router-Link TLV,
  the same format for the sub-TLV defined in <xref target="RFC5329" format="default" sectionFormat="of" derivedContent="RFC5329"/> target="RFC5329"/> is used with
  TLV type 24.</t>
    </section>
    <section anchor="REMOTEIPV6ADDR" numbered="true" toc="include" removeInRFC="false" pn="section-10">
      <name slugifiedName="name-remote-interface-ipv6-addre">Remote anchor="REMOTEIPV6ADDR">
      <name>Remote Interface IPv6 Address Sub-TLV</name>
      <t indent="0" pn="section-10-1">The
      <t>The Remote Interface IPv6 Address sub-TLV is an application-independent attribute of the
  link that is defined in <xref target="RFC5329" format="default" sectionFormat="of" derivedContent="RFC5329"/>. target="RFC5329"/>. Because it is an application-independent attribute, it <bcp14>MUST NOT</bcp14> be advertised in the ASLA sub-TLV. Instead, it <bcp14>MAY</bcp14> be
  advertised as a sub-TLV of the Router-Link TLV inside the OSPFv3 E-Router-LSA <xref target="RFC8362" format="default" sectionFormat="of" derivedContent="RFC8362"/>.</t>
      <t indent="0" pn="section-10-2">To target="RFC8362"/>.</t>
      <t>To advertise the Remote Interface IPv6 Address sub-TLV in the OSPFv3 Router-Link TLV,
  the same format for the sub-TLV defined in <xref target="RFC5329" format="default" sectionFormat="of" derivedContent="RFC5329"/> target="RFC5329"/> is used with
  TLV type 25.</t>
    </section>
    <section numbered="true" toc="include" removeInRFC="false" pn="section-11">
      <name slugifiedName="name-attribute-advertisements-an">Attribute
    <section>
      <name>Attribute Advertisements and Enablement</name>
      <t indent="0" pn="section-11-1">This
      <t>This document defines extensions to support the advertisement of
   application-specific link attributes.</t>
      <t indent="0" pn="section-11-2">There
      <t>There are applications where the application enablement on the link
      is relevant; for example, with RSVP-TE, one needs to make sure that RSVP
      is enabled on the link before sending an RSVP-TE signaling message over it.</t>
      <t indent="0" pn="section-11-3">There
      <t>There are applications where the enablement of the application on the link is
   irrelevant and has nothing to do with the fact that some link attributes are advertised
   for the purpose of such application. An example of this is LFA.</t>
      <t indent="0" pn="section-11-4">Whether
      <t>Whether the presence of link attribute advertisements for a given
   application indicates that the application is enabled on that link
   depends upon the application.  Similarly, whether the absence of link
   attribute advertisements indicates that the application is not
   enabled depends upon the application.</t>
      <t indent="0" pn="section-11-5">In
      <t>In the case of RSVP-TE, the advertisement of application-specific
   link attributes has no implication of RSVP-TE being enabled on that link.
   The RSVP-TE enablement is solely derived from the information carried in
   the OSPFv2 TE Opaque LSA  <xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/> target="RFC3630"/> and OSPFv3 Intra-Area-TE-LSA
   <xref target="RFC5329" format="default" sectionFormat="of" derivedContent="RFC5329"/>.</t>
      <t indent="0" pn="section-11-6">In target="RFC5329"/>.</t>
      <t>In the case of SR Policy, advertisement of application-specific link
   attributes does not indicate enablement of SR Policy.  The advertisements
   are only used to support constraints that may be applied when
   specifying an explicit path.  SR Policy is implicitly enabled on all links
   that are part of the SR-enabled topology independent of
   the existence of link attribute advertisements.</t>
      <t indent="0" pn="section-11-7">In
      <t>In the case of LFA, the advertisement of application-specific link
   attributes does not indicate enablement of LFA on that link.
   Enablement is controlled by local configuration.</t>
      <t indent="0" pn="section-11-8">In
      <t>In the future, if additional standard applications are defined to
   use this mechanism, the specification defining this use <bcp14>MUST</bcp14> define
   the relationship between application-specific link attribute
   advertisements and enablement for that application.</t>
      <t indent="0" pn="section-11-9">This
      <t>This document allows the advertisement of application-specific link
   attributes with no application identifiers, i.e., both the Standard
   Application Identifier Bit Mask SABM and the User-Defined Application
   Identifier Bit Mask UDABM are not present (see <xref target="ADVAPPVAL" format="default" sectionFormat="of" derivedContent="Section 5"/>). target="ADVAPPVAL"/>).
   This supports the use of the link attribute by any application.  In the presence of
   an application where the advertisement of link attributes is used to infer the enablement of an application on
   that link (e.g., RSVP-TE), the absence of the application identifier
   leaves ambiguous whether that application is enabled on such a link.
   This needs to be considered when making use of the "any application"
   encoding.</t>
    </section>
    <section numbered="true" toc="include" removeInRFC="false" pn="section-12">
      <name slugifiedName="name-deployment-considerations">Deployment
    <section>
      <name>Deployment Considerations</name>
      <section anchor="LEGACY_OSPF" numbered="true" toc="include" removeInRFC="false" pn="section-12.1">
        <name slugifiedName="name-use-of-legacy-rsvp-te-lsa-a">Use anchor="LEGACY_OSPF">
        <name>Use of Legacy RSVP-TE LSA Advertisements</name>
        <t indent="0" pn="section-12.1-1">Bit
        <t>Bit identifiers for standard applications are defined in <xref target="ADVAPPVAL" format="default" sectionFormat="of" derivedContent="Section 5"/>. target="ADVAPPVAL"/>.
   All of the identifiers defined in this document are associated with
   applications that were already deployed in some networks prior to
   the writing of this document.  Therefore, such applications have been
   deployed using the RSVP-TE LSA advertisements.  The standard applications
   defined in this document may continue to use RSVP-TE LSA advertisements
   for a given link so long as at least one of the following conditions
   is true:

        </t>
        <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-12.1-2">
          <li pn="section-12.1-2.1">The
        <ul>
          <li>The application is RSVP-TE.</li>
          <li pn="section-12.1-2.2">The
          <li>The application is SR Policy or LFA, and RSVP-TE is not deployed
      anywhere in the network.</li>
          <li pn="section-12.1-2.3">The
          <li>The application is SR Policy or LFA, RSVP-TE is deployed in the
      network, and both the set of links on which SR Policy and/or LFA
      advertisements are required and the attribute values used by SR Policy
      and/or LFA on all such links are fully congruent with the links and
      attribute values used by RSVP-TE.</li>
        </ul>
        <t indent="0" pn="section-12.1-3">Under
        <t>Under the conditions defined above, implementations that support the
   extensions defined in this document have the choice of using RSVP-TE LSA
   advertisements or application-specific advertisements in support of
   SR Policy and/or LFA.  This will require implementations to provide
   controls specifying which types of advertisements are to be sent and processed on receipt for these applications.  Further discussion of
   the associated issues can be found in <xref target="IBCMC" format="default" sectionFormat="of" derivedContent="Section 12.3"/>.</t>
        <t indent="0" pn="section-12.1-4">New target="IBCMC"/>.</t>
        <t>New applications that future documents define to make use of the
   advertisements defined in this document <bcp14>MUST NOT</bcp14> make use of RSVP-TE LSA
   advertisements. This simplifies deployment of new applications by
   eliminating the need to support multiple ways to advertise attributes
   for the new applications.</t>
      </section>
      <section anchor="ZLABM" numbered="true" toc="include" removeInRFC="false" pn="section-12.2">
        <name slugifiedName="name-use-zero-length-">Use anchor="ZLABM">
        <name>Use of Zero-Length Application Identifier Bit Masks</name>
        <t indent="0" pn="section-12.2-1">Link
        <t>Link attribute advertisements associated with zero-length Application
   Identifier Bit Masks for both standard applications and user-defined
   applications are usable by any application, subject to the
   restrictions specified in Section 4.2. <xref target="ADVAPPVAL"/>.  If support for a new
   application is introduced on any node in a network in the presence of
   such advertisements, the new application will use these
   advertisements,
   advertisements when the aforementioned restrictions are met.  If
   this is not what is intended, then existing link attribute
   advertisements MUST <bcp14>MUST</bcp14> be readvertised with an explicit set of
   applications specified before a new application is introduced.</t>
      </section>
      <section anchor="IBCMC" numbered="true" toc="include" removeInRFC="false" pn="section-12.3">
        <name slugifiedName="name-interoperability-backwards-">Interoperability, anchor="IBCMC">
        <name>Interoperability, Backwards Compatibility, and Migration Concerns</name>
        <t indent="0" pn="section-12.3-1">Existing
        <t>Existing deployments of RSVP-TE, SR Policy, and/or LFA utilize the
        legacy advertisements listed in <xref target="LEG_ADV" format="default" sectionFormat="of" derivedContent="Section 3"/>. target="LEG_ADV"/>. Routers that do not
        support the extensions defined in this document will only process
        legacy advertisements and are likely to infer that RSVP-TE is enabled
        on the links for which legacy advertisements exist. It is expected
        that deployments using the legacy advertisements will persist for a
        significant period of time. Therefore, deployments using the
        extensions defined in this document in the presence of routers that
        do not support these extensions need to be able to interoperate with
        the use of legacy advertisements by the legacy routers. The following subsections
        discuss interoperability and backwards-compatibility concerns for a number of
        deployment scenarios.</t>
        <section anchor="MACARSVP" numbered="true" toc="include" removeInRFC="false" pn="section-12.3.1">
          <name slugifiedName="name-multiple-applications-commo">Multiple anchor="MACARSVP">
          <name>Multiple Applications: Common Attributes with  RSVP-TE</name>
          <t indent="0" pn="section-12.3.1-1">In
          <t>In cases where multiple applications are utilizing a given link,
          one of the applications is RSVP-TE, and all link attributes for a
          given link are common to the set of applications utilizing that
          link, interoperability is achieved by using legacy advertisements for RSVP-TE.
          Attributes for applications other than RSVP-TE <bcp14>MUST</bcp14> be advertised using
          application-specific advertisements. This results in duplicate
          advertisements for those attributes.</t>
        </section>
        <section anchor="MAALLNS" numbered="true" toc="include" removeInRFC="false" pn="section-12.3.2">
          <name slugifiedName="name-multiple-applications-some-">Multiple anchor="MAALLNS">
          <name>Multiple Applications: Some Attributes Not Shared with RSVP-TE</name>
          <t indent="0" pn="section-12.3.2-1">In
          <t>In cases where one or more applications other than RSVP-TE are
          utilizing a given link and one or more link attribute values are not
          shared with RSVP-TE, interoperability is achieved by using legacy advertisements
          for RSVP-TE. Attributes for applications other than RSVP-TE <bcp14>MUST</bcp14> be advertised using
          application-specific advertisements. In cases where some link attributes are
          shared with RSVP-TE, this requires duplicate advertisements for those attributes.</t>
        </section>
        <section anchor="LEGACY" numbered="true" toc="include" removeInRFC="false" pn="section-12.3.3">
          <name slugifiedName="name-interoperability-with-legac">Interoperability anchor="LEGACY">
          <name>Interoperability with Legacy Routers</name>
          <t indent="0" pn="section-12.3.3-1">
          <t>
	   For the standard applications defined in this document,
	    routers that do not
	    support the extensions defined in this document will send and
	    receive only legacy link attribute advertisements. In addition,
	    the link attribute values associated with these applications
	    are always shared since legacy routers have no way of advertising or
	    processing application-specific values. So long as there is any
	    legacy router in the network that has any of the standard
	    applications
	    defined in this document enabled, all routers <bcp14>MUST</bcp14>
	    continue to advertise link attributes for these applications using
	    only legacy advertisements. ASLA advertisements for these
	    applications <bcp14>MUST NOT</bcp14> be sent.  Once all legacy
	    routers have been upgraded, migration from legacy advertisements
	    to ASLA advertisements can be achieved via the following steps:
          </t>
          <ol type="%d)" indent="adaptive" spacing="normal" start="1" pn="section-12.3.3-2"> type="%d)">
	   <li pn="section-12.3.3-2.1" derivedCounter="1)">Send new application-specific advertisements while continuing to
	   advertise using the legacy advertisement (all advertisements are
	   then duplicated). Receiving routers continue to use legacy advertisements.</li>
            <li pn="section-12.3.3-2.2" derivedCounter="2)">Enable the use of the application-specific advertisements on
	   all routers.</li>
            <li pn="section-12.3.3-2.3" derivedCounter="3)">Keep legacy advertisements if needed for RSVP-TE purposes.</li>
          </ol>
          <t indent="0" pn="section-12.3.3-3">When
          <t>When the migration is complete, it then becomes possible to
          advertise incongruent values per application on a given link.</t>
          <t indent="0" pn="section-12.3.3-4">Documents
          <t>Documents defining new applications that make use of the
          application-specific advertisements defined in this document <bcp14>MUST</bcp14>
          discuss interoperability and backwards-compatibility issues that
          could occur in the presence of routers that do not support the new
          application.</t>
        </section>
        <section anchor="APPRSVP" numbered="true" toc="include" removeInRFC="false" pn="section-12.3.4">
          <name slugifiedName="name-use-of-application-specific">Use anchor="APPRSVP">
          <name>Use of Application-Specific Advertisements for RSVP-TE</name>
          <t indent="0" pn="section-12.3.4-1">The
          <t>The extensions defined in this document support RSVP-TE as one of
          the supported applications. It is, however, <bcp14>RECOMMENDED</bcp14> to advertise all
          link attributes for RSVP-TE in the existing OSPFv2 TE Opaque LSA
          <xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/> target="RFC3630"/> and OSPFv3 Intra-Area-TE-LSA <xref target="RFC5329" format="default" sectionFormat="of" derivedContent="RFC5329"/> target="RFC5329"/>
          to maintain backwards compatibility. RSVP-TE can eventually
          utilize the application-specific advertisements for newly defined
	  link attributes that are defined as application specific.</t>
          <t indent="0" pn="section-12.3.4-2">Link
          <t>Link attributes that are not allowed to be advertised in the ASLA sub-TLV,
          such as maximum reservable link bandwidth and unreserved bandwidth, <bcp14>MUST</bcp14> use the
          OSPFv2 TE Opaque LSA <xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/> target="RFC3630"/> and OSPFv3 Intra-Area-TE-LSA
          <xref target="RFC5329" format="default" sectionFormat="of" derivedContent="RFC5329"/> target="RFC5329"/> and <bcp14>MUST NOT</bcp14> be advertised in the ASLA sub-TLV.</t>
        </section>
      </section>
    </section>
    <section numbered="true" toc="include" removeInRFC="false" pn="section-13">
      <name slugifiedName="name-security-considerations">Security
    <section>
      <name>Security Considerations</name>
      <t indent="0" pn="section-13-1">Existing
      <t>Existing security extensions as described in <xref target="RFC2328" format="default" sectionFormat="of" derivedContent="RFC2328"/>,
       <xref target="RFC5340" format="default" sectionFormat="of" derivedContent="RFC5340"/>, target="RFC2328"/>,
       <xref target="RFC5340"/>, and <xref target="RFC8362" format="default" sectionFormat="of" derivedContent="RFC8362"/> target="RFC8362"/> apply to extensions
       defined in this document. While OSPF is under a single administrative domain,
       there can be deployments where potential attackers have access to one or more
       networks in the OSPF routing domain. In these deployments, stronger authentication
       mechanisms such as those specified in <xref target="RFC5709" format="default" sectionFormat="of" derivedContent="RFC5709"/>,
       <xref target="RFC7474" format="default" sectionFormat="of" derivedContent="RFC7474"/>, <xref target="RFC4552" format="default" sectionFormat="of" derivedContent="RFC4552"/>, target="RFC5709"/>,
       <xref target="RFC7474"/>, <xref target="RFC4552"/>, or
       <xref target="RFC7166" format="default" sectionFormat="of" derivedContent="RFC7166"/> target="RFC7166"/> <bcp14>SHOULD</bcp14> be
      used.</t>
      <t indent="0" pn="section-13-2">Implementations
      <t>Implementations must ensure that if any of the TLVs and sub-TLVs
      defined in this document are malformed, they are detected and do not
      facilitate a vulnerability for attackers to crash or otherwise compromise
      the OSPF router or routing process. Reception of a
      malformed TLV or sub-TLV <bcp14>SHOULD</bcp14> be counted and/or logged
      for further analysis. Logging of malformed TLVs and sub-TLVs
      <bcp14>SHOULD</bcp14> be rate-limited to prevent a denial-of-service
      (DoS) attack (distributed or otherwise) from overloading the OSPF
      control plane.</t>
      <t indent="0" pn="section-13-3">This
      <t>This document defines a new an improved way to advertise link attributes.
      Tampering with the information defined in this document may have an
      effect on applications using it, including impacting traffic
      engineering, TE, which uses various link attributes for its path
      computation. This is similar in nature to the impacts associated with,
      for example, <xref target="RFC3630" format="default" sectionFormat="of" derivedContent="RFC3630"/>. target="RFC3630"/>.  As the
      advertisements defined in this document limit the scope to specific
      applications, the impact of tampering is similarly limited in scope.</t>
    </section>
    <section anchor="IANA" numbered="true" toc="include" removeInRFC="false" pn="section-14">
      <name slugifiedName="name-iana-considerations">IANA anchor="IANA">
      <name>IANA Considerations</name>
      <t indent="0" pn="section-14-1">This
      <t>This specification updates two existing registries:
      </t>
      <ul bare="false" empty="false" indent="3" spacing="normal" pn="section-14-2">
        <li pn="section-14-2.1">the
      <ul>
        <li>the "OSPFv2 Extended Link TLV Sub-TLVs" registry</li>
        <li pn="section-14-2.2">the
        <li>the "OSPFv3 Extended-LSA Sub-TLVs" registry</li>
      </ul>
      <t indent="0" pn="section-14-3">The new
      <t>The values defined in this document have been allocated using the
      IETF Review procedure as described in
      <xref target="RFC8126" format="default" sectionFormat="of" derivedContent="RFC8126"/>.</t> target="RFC8126"/>.</t>
      <section anchor="OSPFV2IANA" numbered="true" toc="include" removeInRFC="false" pn="section-14.1">
        <name slugifiedName="name-ospfv2">OSPFv2</name>
        <t indent="0" pn="section-14.1-1">The anchor="OSPFV2IANA">
        <name>OSPFv2</name>
        <t>The "OSPFv2 Extended Link TLV Sub-TLVs" registry <xref target="RFC7684" format="default" sectionFormat="of" derivedContent="RFC7684"/> target="RFC7684"/> defines sub-TLVs at any level of
        nesting for OSPFv2 Extended Link TLVs. IANA has assigned the following
        sub-TLV types from in the "OSPFv2 Extended Link TLV Sub-TLVs" registry:
        </t>
        <dl indent="3" newline="false" spacing="normal" pn="section-14.1-2">
          <dt pn="section-14.1-2.1">10:</dt>
          <dd pn="section-14.1-2.2"> Application-Specific
        <dl>
          <dt>10:</dt>
          <dd>Application-Specific Link Attributes</dd>
          <dt pn="section-14.1-2.3">11:</dt>
          <dd pn="section-14.1-2.4"> Shared
          <dt>11:</dt>
          <dd>Shared Risk Link Group</dd>
          <dt pn="section-14.1-2.5">12:</dt>
          <dd pn="section-14.1-2.6"> Unidirectional
          <dt>12:</dt>
          <dd>Unidirectional Link Delay</dd>
          <dt pn="section-14.1-2.7">13:</dt>
          <dd pn="section-14.1-2.8"> Min/Max
          <dt>13:</dt>
          <dd>Min/Max Unidirectional Link Delay</dd>
          <dt pn="section-14.1-2.9">14:</dt>
          <dd pn="section-14.1-2.10"> Unidirectional
          <dt>14:</dt>
          <dd>Unidirectional Delay Variation</dd>
          <dt pn="section-14.1-2.11">15:</dt>
          <dd pn="section-14.1-2.12"> Unidirectional
          <dt>15:</dt>
          <dd>Unidirectional Link Loss</dd>
          <dt pn="section-14.1-2.13">16:</dt>
          <dd pn="section-14.1-2.14"> Unidirectional
          <dt>16:</dt>
          <dd>Unidirectional Residual Bandwidth</dd>
          <dt pn="section-14.1-2.15">17:</dt>
          <dd pn="section-14.1-2.16"> Unidirectional
          <dt>17:</dt>
          <dd>Unidirectional Available Bandwidth</dd>
          <dt pn="section-14.1-2.17">18:</dt>
          <dd pn="section-14.1-2.18"> Unidirectional
          <dt>18:</dt>
          <dd>Unidirectional Utilized Bandwidth</dd>
          <dt pn="section-14.1-2.19">19:</dt>
          <dd pn="section-14.1-2.20"> Administrative
          <dt>19:</dt>
          <dd>Administrative Group</dd>
          <dt pn="section-14.1-2.21">20:</dt>
          <dd pn="section-14.1-2.22"> Extended
          <dt>20:</dt>
          <dd>Extended Administrative Group</dd>
          <dt pn="section-14.1-2.23">22:</dt>
          <dd pn="section-14.1-2.24"> TE
          <dt>22:</dt>
          <dd>TE Metric</dd>
          <dt pn="section-14.1-2.25">23:</dt>
          <dd pn="section-14.1-2.26"> Maximum
          <dt>23:</dt>
          <dd>Maximum link bandwidth</dd>
        </dl>
      </section>
      <section anchor="OSPFV3IANA" numbered="true" toc="include" removeInRFC="false" pn="section-14.2">
        <name slugifiedName="name-ospfv3">OSPFv3</name>
        <t indent="0" pn="section-14.2-1">The anchor="OSPFV3IANA">
        <name>OSPFv3</name>
        <t>The "OSPFv3 Extended-LSA Sub-TLVs" registry <xref target="RFC8362" format="default" sectionFormat="of" derivedContent="RFC8362"/> target="RFC8362"/> defines
	sub-TLVs at any level of nesting for OSPFv3
        Extended LSAs. IANA has assigned the following sub-TLV types from in the
        "OSPFv3 Extended-LSA Sub-TLVs" registry:
        </t>
        <dl indent="3" newline="false" spacing="normal" pn="section-14.2-2">
          <dt pn="section-14.2-2.1">11:</dt>
          <dd pn="section-14.2-2.2"> Application-Specific
        <dl>
          <dt>11:</dt>
          <dd>Application-Specific Link Attributes</dd>
          <dt pn="section-14.2-2.3">12:</dt>
          <dd pn="section-14.2-2.4"> Shared
          <dt>12:</dt>
          <dd>Shared Risk Link Group</dd>
          <dt pn="section-14.2-2.5">13:</dt>
          <dd pn="section-14.2-2.6"> Unidirectional
          <dt>13:</dt>
          <dd>Unidirectional Link Delay</dd>
          <dt pn="section-14.2-2.7">14:</dt>
          <dd pn="section-14.2-2.8"> Min/Max
          <dt>14:</dt>
          <dd>Min/Max Unidirectional Link Delay</dd>
          <dt pn="section-14.2-2.9">15:</dt>
          <dd pn="section-14.2-2.10"> Unidirectional
          <dt>15:</dt>
          <dd>Unidirectional Delay Variation</dd>
          <dt pn="section-14.2-2.11">16:</dt>
          <dd pn="section-14.2-2.12"> Unidirectional
          <dt>16:</dt>
          <dd>Unidirectional Link Loss</dd>
          <dt pn="section-14.2-2.13">17:</dt>
          <dd pn="section-14.2-2.14"> Unidirectional
          <dt>17:</dt>
          <dd>Unidirectional Residual Bandwidth</dd>
          <dt pn="section-14.2-2.15">18:</dt>
          <dd pn="section-14.2-2.16"> Unidirectional
          <dt>18:</dt>
          <dd>Unidirectional Available Bandwidth</dd>
          <dt pn="section-14.2-2.17">19:</dt>
          <dd pn="section-14.2-2.18"> Unidirectional
          <dt>19:</dt>
          <dd>Unidirectional Utilized Bandwidth</dd>
          <dt pn="section-14.2-2.19">20:</dt>
          <dd pn="section-14.2-2.20"> Administrative
          <dt>20:</dt>
          <dd>Administrative Group</dd>
          <dt pn="section-14.2-2.21">21:</dt>
          <dd pn="section-14.2-2.22"> Extended
          <dt>21:</dt>
          <dd>Extended Administrative Group</dd>
          <dt pn="section-14.2-2.23">22:</dt>
          <dd pn="section-14.2-2.24"> TE
          <dt>22:</dt>
          <dd>TE Metric</dd>
          <dt pn="section-14.2-2.25">23:</dt>
          <dd pn="section-14.2-2.26"> Maximum
          <dt>23:</dt>
          <dd>Maximum link bandwidth</dd>
          <dt pn="section-14.2-2.27">24:</dt>
          <dd pn="section-14.2-2.28"> Local
          <dt>24:</dt>
          <dd>Local Interface IPv6 Address</dd>
          <dt pn="section-14.2-2.29">25:</dt>
          <dd pn="section-14.2-2.30"> Remote
          <dt>25:</dt>
          <dd>Remote Interface IPv6 Address</dd>
        </dl>
      </section>
    </section>
    <section anchor="changes-to-rfc8920" numbered="true" toc="include" removeInRFC="false" pn="section-15">
      <name slugifiedName="name-changes-to-rfc8920">Changes anchor="changes-to-rfc8920">
      <name>Changes to RFC 8920</name>
      <t indent="0" pn="section-15-1">Discussion
      <t>Discussion within the LSR WG indicated that there was confusion regarding
      the use of ASLA advertisements that had a zero length zero-length SABM/UDABM.
      The discussion can be seen by searching the LSR WG mailing
   list archives for the thread "Proposed Errata for RFCs 8919/8920"
   starting on 15 June 2021. </t>
      <t indent="0" pn="section-15-2">Changes
      <t>Changes to Section 5 <xref target="ADVAPPVAL"/> have been introduced to clarify normative
      behavior in the presence of such advertisements. RFC 8920 <xref target="RFC8920"/> defines advertising link attributes with zero
      length Standard Application Bit Mask (SABM) zero-length
      SABM and zero length User
      Defined ApplicationBit Mask (UDABM) zero-length UDABM as a means of advertising link
      attributes that can be used by any application. However, the text uses
      the word "permitted", suggesting that the use of such advertisements
      is "optional". Such an interpretation could lead to interoperability
      issues and is not what was intended.</t>
      <t indent="0" pn="section-15-3">The
      <t>The replacement text makes explicit the specific conditions when such
      advertisements <bcp14>MUST</bcp14> be used and the specific conditions under which they <bcp14>MUST NOT</bcp14>
      be used.</t>
      <t indent="0" pn="section-15-4">A new
      <t>A subsection discussing the use of zero-length Application Identifier Bit Masks has been added for greater consistency with <xref target="RFC8919" format="default" sectionFormat="of" derivedContent="RFC8919"/>. target="RFC9479"/>. See <xref target="ZLABM" format="default" sectionFormat="of" derivedContent="Section 12.2"/>.</t> target="ZLABM"/>.</t>
    </section>
  </middle>
  <back>
    <displayreference target="RFC9256" to="SEGMENT-ROUTING"/>
    <references pn="section-16">
      <name slugifiedName="name-references">References</name>
      <references pn="section-16.1">
        <name slugifiedName="name-normative-references">Normative
    <references>
      <name>References</name>
      <references>
        <name>Normative References</name>
<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 initials="S." surname="Bradner" fullname="S. Bradner">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="1997" month="March"/>
            <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="RFC2328" target="https://www.rfc-editor.org/info/rfc2328" quoteTitle="true" derivedAnchor="RFC2328">
          <front>
            <title>OSPF Version 2</title>
            <author initials="J." surname="Moy" fullname="J. Moy">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="1998" month="April"/>
            <abstract>
              <t indent="0">This memo documents version 2 of the OSPF protocol.  OSPF is a link- state routing protocol.  [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="STD" value="54"/>
          <seriesInfo name="RFC" value="2328"/>
          <seriesInfo name="DOI" value="10.17487/RFC2328"/>
        </reference>
        <reference anchor="RFC3630" target="https://www.rfc-editor.org/info/rfc3630" quoteTitle="true" derivedAnchor="RFC3630">
          <front>
            <title>Traffic Engineering (TE) Extensions to OSPF Version 2</title>
            <author initials="D." surname="Katz" fullname="D. Katz">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="K." surname="Kompella" fullname="K. Kompella">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="D." surname="Yeung" fullname="D. Yeung">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2003" month="September"/>
            <abstract>
              <t indent="0">This document describes extensions to the OSPF protocol version 2 to support intra-area Traffic Engineering (TE), using Opaque Link State Advertisements.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="3630"/>
          <seriesInfo name="DOI" value="10.17487/RFC3630"/>
        </reference>
        <reference anchor="RFC4203" target="https://www.rfc-editor.org/info/rfc4203" quoteTitle="true" derivedAnchor="RFC4203">
          <front>
            <title>OSPF Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)</title>
            <author initials="K." surname="Kompella" fullname="K. Kompella" role="editor">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="Y." surname="Rekhter" fullname="Y. Rekhter" role="editor">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2005" month="October"/>
            <abstract>
              <t indent="0">This document specifies encoding of extensions to the OSPF routing protocol in support of Generalized Multi-Protocol Label Switching (GMPLS).  [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="4203"/>
          <seriesInfo name="DOI" value="10.17487/RFC4203"/>
        </reference>
        <reference anchor="RFC5329" target="https://www.rfc-editor.org/info/rfc5329" quoteTitle="true" derivedAnchor="RFC5329">
          <front>
            <title>Traffic Engineering Extensions to OSPF Version 3</title>
            <author initials="K." surname="Ishiguro" fullname="K. Ishiguro">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="V." surname="Manral" fullname="V. Manral">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="A." surname="Davey" fullname="A. Davey">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="A." surname="Lindem" fullname="A. Lindem" role="editor">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2008" month="September"/>
            <abstract>
              <t indent="0">This document describes extensions to OSPFv3 to support intra-area Traffic Engineering (TE).  This document extends OSPFv2 TE to handle IPv6 networks.  A new TLV and several new sub-TLVs are defined to support IPv6 networks.  [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="5329"/>
          <seriesInfo name="DOI" value="10.17487/RFC5329"/>
        </reference>
        <reference anchor="RFC5340" target="https://www.rfc-editor.org/info/rfc5340" quoteTitle="true" derivedAnchor="RFC5340">
          <front>
            <title>OSPF for IPv6</title>
            <author initials="R." surname="Coltun" fullname="R. Coltun">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="D." surname="Ferguson" fullname="D. Ferguson">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="J." surname="Moy" fullname="J. Moy">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="A." surname="Lindem" fullname="A. Lindem">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2008" month="July"/>
            <abstract>
              <t indent="0">This document describes the modifications to OSPF to support version 6 of the Internet Protocol (IPv6).  The fundamental mechanisms of OSPF (flooding, Designated Router (DR) election, area support, Short Path First (SPF) calculations, etc.) remain unchanged.  However, some changes have been necessary, either due to changes in protocol semantics between IPv4 and IPv6, or simply to handle the increased address size of IPv6.  These modifications will necessitate incrementing the protocol version from version 2 to version 3.  OSPF for IPv6 is also referred to as OSPF version 3 (OSPFv3).</t>
              <t indent="0">Changes between OSPF for IPv4, OSPF Version 2, and OSPF for IPv6 as described herein include the following.  Addressing semantics have been removed from OSPF packets and the basic Link State Advertisements (LSAs).  New LSAs have been created to carry IPv6 addresses and prefixes.  OSPF now runs on a per-link basis rather than on a per-IP-subnet basis.  Flooding scope for LSAs has been generalized.  Authentication has been removed from the OSPF protocol and instead relies on IPv6's Authentication Header and Encapsulating Security Payload (ESP).</t>
              <t indent="0">Even with larger IPv6 addresses, most packets in OSPF for IPv6 are almost as compact as those in OSPF for IPv4.  Most fields and packet- size limitations present in OSPF for IPv4 have been relaxed.  In addition, option handling has been made more flexible.</t>
              <t indent="0">All of OSPF for IPv4's optional capabilities, including demand circuit support and Not-So-Stubby Areas (NSSAs), are also supported in OSPF for IPv6.  [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="5340"/>
          <seriesInfo name="DOI" value="10.17487/RFC5340"/>
        </reference>
        <reference anchor="RFC7308" target="https://www.rfc-editor.org/info/rfc7308" quoteTitle="true" derivedAnchor="RFC7308">
          <front>
            <title>Extended Administrative Groups in MPLS Traffic Engineering (MPLS-TE)</title>
            <author initials="E." surname="Osborne" fullname="E. Osborne">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2014" month="July"/>
            <abstract>
              <t indent="0">MPLS Traffic Engineering (MPLS-TE) advertises 32 administrative groups (commonly referred to as "colors" or "link colors") using the Administrative Group sub-TLV.  This is defined for OSPFv2 (RFC 3630), OSPFv3 (RFC 5329) and IS-IS (RFC 5305).</t>
              <t indent="0">This document adds a sub-TLV to the IGP TE extensions, "Extended Administrative Group".  This sub-TLV provides for additional administrative groups (link colors) beyond the current limit of 32.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="7308"/>
          <seriesInfo name="DOI" value="10.17487/RFC7308"/>
        </reference>
        <reference anchor="RFC7471" target="https://www.rfc-editor.org/info/rfc7471" quoteTitle="true" derivedAnchor="RFC7471">
          <front>
            <title>OSPF Traffic Engineering (TE) Metric Extensions</title>
            <author initials="S." surname="Giacalone" fullname="S. Giacalone">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="D." surname="Ward" fullname="D. Ward">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="J." surname="Drake" fullname="J. Drake">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="A." surname="Atlas" fullname="A. Atlas">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="S." surname="Previdi" fullname="S. Previdi">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2015" month="March"/>
            <abstract>
              <t indent="0">In certain networks, such as, but not limited to, financial information networks (e.g., stock market data providers), network performance information (e.g., link propagation delay) is becoming critical to data path selection.</t>
              <t indent="0">This document describes common extensions to RFC 3630 "Traffic                                           Engineering (TE) Extensions to OSPF Version 2" and RFC 5329 "Traffic                                     Engineering Extensions to OSPF Version 3" to enable network performance information to be distributed in a scalable fashion.  The information distributed using OSPF TE Metric Extensions can then be used to make path selection decisions based on network performance.</t>
              <t indent="0">Note that this document only covers the mechanisms by which network performance information is distributed.  The mechanisms for measuring network performance information or using that information, once distributed, are outside the scope of this document.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="7471"/>
          <seriesInfo name="DOI" value="10.17487/RFC7471"/>
        </reference>
        <reference anchor="RFC7684" target="https://www.rfc-editor.org/info/rfc7684" quoteTitle="true" derivedAnchor="RFC7684">
          <front>
            <title>OSPFv2 Prefix/Link Attribute Advertisement</title>
            <author initials="P." surname="Psenak" fullname="P. Psenak">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="H." surname="Gredler" fullname="H. Gredler">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="R." surname="Shakir" fullname="R. Shakir">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="W." surname="Henderickx" fullname="W. Henderickx">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="J." surname="Tantsura" fullname="J. Tantsura">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="A." surname="Lindem" fullname="A. Lindem">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2015" month="November"/>
            <abstract>
              <t indent="0">OSPFv2 requires functional extension beyond what can readily be done with the fixed-format Link State Advertisements (LSAs) as described in RFC 2328.  This document defines OSPFv2 Opaque LSAs based on Type-Length-Value (TLV) tuples that can be used to associate additional attributes with prefixes or links.  Depending on the application, these prefixes and links may or may not be advertised in the fixed-format LSAs.  The OSPFv2 Opaque LSAs are optional and fully backward compatible.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="7684"/>
          <seriesInfo name="DOI" value="10.17487/RFC7684"/>
        </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 initials="B." surname="Leiba" fullname="B. Leiba">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2017" month="May"/>
            <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="RFC8362" target="https://www.rfc-editor.org/info/rfc8362" quoteTitle="true" derivedAnchor="RFC8362">
          <front>
            <title>OSPFv3 Link State Advertisement (LSA) Extensibility</title>
            <author initials="A." surname="Lindem" fullname="A. Lindem">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="A." surname="Roy" fullname="A. Roy">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="D." surname="Goethals" fullname="D. Goethals">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="V." surname="Reddy Vallem" fullname="V. Reddy Vallem">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="F." surname="Baker" fullname="F. Baker">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2018" month="April"/>
            <abstract>
              <t indent="0">OSPFv3 requires functional extension beyond what can readily be done with the fixed-format Link State Advertisement (LSA) as described in RFC 5340.  Without LSA extension, attributes associated with OSPFv3 links and advertised IPv6 prefixes must be advertised in separate LSAs and correlated to the fixed-format LSAs.  This document extends the LSA format by encoding the existing OSPFv3 LSA information in Type-Length-Value (TLV) tuples and allowing advertisement of additional information with additional TLVs.  Backward-compatibility mechanisms are also described.</t>
              <t indent="0">This document updates RFC 5340, "OSPF for IPv6", and RFC 5838, "Support of Address Families in OSPFv3", by providing TLV-based encodings for the base OSPFv3 unicast support and OSPFv3 address family support.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8362"/>
          <seriesInfo name="DOI" value="10.17487/RFC8362"/>
        </reference>
        <reference anchor="RFC8919" target="https://www.rfc-editor.org/info/rfc8919" quoteTitle="true" derivedAnchor="RFC8919"> anchor="RFC9479" target="https://www.rfc-editor.org/info/rfc9479">
  <front>
    <title>IS-IS Application-Specific Link Attributes</title>
    <author initials="L" initials="L." surname="Ginsberg" fullname="Les Ginsberg">
              <organization showOnFrontPage="true"/>
    </author>
    <author initials="P" initials="P." surname="Psenak" fullname="Peter Psenak">
              <organization showOnFrontPage="true"/>
    </author>
    <author initials="S" initials="S." surname="Previdi" fullname="Stefano Previdi">
              <organization showOnFrontPage="true"/>
    </author>
    <author initials="W" initials="W." surname="Henderickx" fullname="Wim Henderickx">
              <organization showOnFrontPage="true"/>
    </author>
    <author initials="J" initials="J." surname="Drake" fullname="John Drake">
              <organization showOnFrontPage="true"/>
    </author>
    <date month="October" year="2020"/> year="2023"/>
  </front>
  <seriesInfo name="RFC" value="8919"/> value="9479"/>
  <seriesInfo name="DOI" value="10.17487/RFC8919"/> value="10.17487/RFC9479"/>
</reference>

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<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5340.xml"/>
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<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7684.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8362.xml"/>

      </references>
      <references pn="section-16.2">
        <name slugifiedName="name-informative-references">Informative
      <references>
        <name>Informative References</name>
        <reference anchor="RFC3209" target="https://www.rfc-editor.org/info/rfc3209" quoteTitle="true" derivedAnchor="RFC3209">
          <front>
            <title>RSVP-TE: Extensions to RSVP for LSP Tunnels</title>
            <author initials="D." surname="Awduche" fullname="D. Awduche">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="L." surname="Berger" fullname="L. Berger">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="D." surname="Gan" fullname="D. Gan">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="T." surname="Li" fullname="T. Li">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="V." surname="Srinivasan" fullname="V. Srinivasan">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="G." surname="Swallow" fullname="G. Swallow">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2001" month="December"/>
            <abstract>
              <t indent="0">This document describes the use of RSVP (Resource Reservation Protocol), including all the necessary extensions, to establish label-switched paths (LSPs) in MPLS (Multi-Protocol Label Switching).  Since the flow along an LSP is completely identified by the label applied at the ingress node of the path, these paths may be treated as tunnels.  A key application of LSP tunnels is traffic engineering with MPLS as specified in RFC 2702.  [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="3209"/>
          <seriesInfo name="DOI" value="10.17487/RFC3209"/>
        </reference>
        <reference anchor="RFC4552" target="https://www.rfc-editor.org/info/rfc4552" quoteTitle="true" derivedAnchor="RFC4552">
          <front>
            <title>Authentication/Confidentiality for OSPFv3</title>
            <author initials="M." surname="Gupta" fullname="M. Gupta">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="N." surname="Melam" fullname="N. Melam">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2006" month="June"/>
            <abstract>
              <t indent="0">This document describes means and mechanisms to provide authentication/confidentiality to OSPFv3 using an IPv6 Authentication Header/Encapsulating Security Payload (AH/ESP) extension header.  [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="4552"/>
          <seriesInfo name="DOI" value="10.17487/RFC4552"/>
        </reference>
        <reference anchor="RFC5286" target="https://www.rfc-editor.org/info/rfc5286" quoteTitle="true" derivedAnchor="RFC5286">
          <front>
            <title>Basic Specification for IP Fast Reroute: Loop-Free Alternates</title>
            <author initials="A." surname="Atlas" fullname="A. Atlas" role="editor">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="A." surname="Zinin" fullname="A. Zinin" role="editor">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2008" month="September"/>
            <abstract>
              <t indent="0">This document describes the use of loop-free alternates to provide local protection for unicast traffic in pure IP and MPLS/LDP networks in the event of a single failure, whether link, node, or shared risk link group (SRLG).  The goal of this technology is to reduce the packet loss that happens while routers converge after a topology change due to a failure.  Rapid failure repair is achieved through use of precalculated backup next-hops that are loop-free and safe to use until the distributed network convergence process completes. This simple approach does not require any support from other routers. The extent to which this goal can be met by this specification is dependent on the topology of the network.  [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="5286"/>
          <seriesInfo name="DOI" value="10.17487/RFC5286"/>
        </reference>
        <reference anchor="RFC5709" target="https://www.rfc-editor.org/info/rfc5709" quoteTitle="true" derivedAnchor="RFC5709">
          <front>
            <title>OSPFv2 HMAC-SHA Cryptographic Authentication</title>
            <author initials="M." surname="Bhatia" fullname="M. Bhatia">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="V." surname="Manral" fullname="V. Manral">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="M." surname="Fanto" fullname="M. Fanto">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="R." surname="White" fullname="R. White">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="M." surname="Barnes" fullname="M. Barnes">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="T." surname="Li" fullname="T. Li">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="R." surname="Atkinson" fullname="R. Atkinson">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2009" month="October"/>
            <abstract>
              <t indent="0">This document describes how the National Institute of Standards and Technology (NIST) Secure Hash Standard family of algorithms can be used with OSPF version 2's built-in, cryptographic authentication mechanism.  This updates, but does not supercede, the cryptographic authentication mechanism specified in RFC 2328. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="5709"/>
          <seriesInfo name="DOI" value="10.17487/RFC5709"/>
        </reference>
        <reference anchor="RFC5714" target="https://www.rfc-editor.org/info/rfc5714" quoteTitle="true" derivedAnchor="RFC5714">
          <front>
            <title>IP Fast Reroute Framework</title>
            <author initials="M." surname="Shand" fullname="M. Shand">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="S." surname="Bryant" fullname="S. Bryant">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2010" month="January"/>
            <abstract>
              <t indent="0">This document provides a framework for the development of IP fast- reroute mechanisms that provide protection against link or router failure by invoking locally determined repair paths.  Unlike MPLS fast-reroute, the mechanisms are applicable to a network employing conventional IP routing and forwarding.  This document is not an  Internet Standards Track specification; it is published for informational  purposes.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="5714"/>
          <seriesInfo name="DOI" value="10.17487/RFC5714"/>
        </reference>
        <reference anchor="RFC7166" target="https://www.rfc-editor.org/info/rfc7166" quoteTitle="true" derivedAnchor="RFC7166">
          <front>
            <title>Supporting Authentication Trailer for OSPFv3</title>
            <author initials="M." surname="Bhatia" fullname="M. Bhatia">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="V." surname="Manral" fullname="V. Manral">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="A." surname="Lindem" fullname="A. Lindem">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2014" month="March"/>
            <abstract>
              <t indent="0">Currently, OSPF for IPv6 (OSPFv3) uses IPsec as the only mechanism for authenticating protocol packets.  This behavior is different from authentication mechanisms present in other routing protocols (OSPFv2, Intermediate System to Intermediate System (IS-IS), RIP, and Routing Information Protocol Next Generation (RIPng)).  In some environments, it has been found that IPsec is difficult to configure and maintain and thus cannot be used.  This document defines an alternative mechanism to authenticate OSPFv3 protocol packets so that OSPFv3 does not depend only upon IPsec for authentication.</t>
              <t indent="0">The OSPFv3 Authentication Trailer was originally defined in RFC 6506. This document obsoletes RFC 6506 by providing a revised definition, including clarifications and refinements of the procedures.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="7166"/>
          <seriesInfo name="DOI" value="10.17487/RFC7166"/>
        </reference>
        <reference anchor="RFC7474" target="https://www.rfc-editor.org/info/rfc7474" quoteTitle="true" derivedAnchor="RFC7474">
          <front>
            <title>Security Extension for OSPFv2 When Using Manual Key Management</title>
            <author initials="M." surname="Bhatia" fullname="M. Bhatia">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="S." surname="Hartman" fullname="S. Hartman">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="D." surname="Zhang" fullname="D. Zhang">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="A." surname="Lindem" fullname="A. Lindem" role="editor">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2015" month="April"/>
            <abstract>
              <t indent="0">The current OSPFv2 cryptographic authentication mechanism as defined in RFCs 2328 and 5709 is vulnerable to both inter-session and intra- session replay attacks when using manual keying.  Additionally, the existing cryptographic authentication mechanism does not cover the IP header.  This omission can be exploited to carry out various types of attacks.</t>
              <t indent="0">This document defines changes to the authentication sequence number mechanism that will protect OSPFv2 from both inter-session and intra- session replay attacks when using manual keys for securing OSPFv2 protocol packets.  Additionally, we also describe some changes in the cryptographic hash computation that will eliminate attacks resulting from OSPFv2 not protecting the IP header.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="7474"/>
          <seriesInfo name="DOI" value="10.17487/RFC7474"/>
        </reference>
        <reference anchor="RFC7855" target="https://www.rfc-editor.org/info/rfc7855" quoteTitle="true" derivedAnchor="RFC7855">
          <front>
            <title>Source Packet Routing in Networking (SPRING) Problem Statement and Requirements</title>
            <author initials="S." surname="Previdi" fullname="S. Previdi" role="editor">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="C." surname="Filsfils" fullname="C. Filsfils" role="editor">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="B." surname="Decraene" fullname="B. Decraene">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="S." surname="Litkowski" fullname="S. Litkowski">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="M." surname="Horneffer" fullname="M. Horneffer">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="R." surname="Shakir" fullname="R. Shakir">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2016" month="May"/>
            <abstract>
              <t indent="0">The ability for a node to specify a forwarding path, other than the normal shortest path, that a particular packet will traverse, benefits a number of network functions.  Source-based routing mechanisms have previously been specified for network protocols but have not seen widespread adoption.  In this context, the term "source" means "the point at which the explicit route is imposed"; therefore, it is not limited to the originator of the packet (i.e., the node imposing the explicit route may be the ingress node of an operator's network).</t>
              <t indent="0">This document outlines various use cases, with their requirements, that need to be taken into account by the Source Packet Routing in Networking (SPRING) architecture for unicast traffic.  Multicast use cases and requirements are out of scope for this document.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="7855"/>
          <seriesInfo name="DOI" value="10.17487/RFC7855"/>
        </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 initials="M." surname="Cotton" fullname="M. Cotton">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="B." surname="Leiba" fullname="B. Leiba">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="T." surname="Narten" fullname="T. Narten">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2017" month="June"/>
            <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="RFC9256" quoteTitle="true" derivedAnchor="SEGMENT-ROUTING">
          <front>
            <title>Segment Routing Policy Architecture</title>
            <author fullname="Clarence Filsfils">
              <organization showOnFrontPage="true">Cisco Systems</organization>
            </author>
            <author fullname="Ketan Talaulikar">
              <organization showOnFrontPage="true">Cisco Systems</organization>
            </author>
            <author fullname="Daniel Voyer">
              <organization showOnFrontPage="true">Bell Canada</organization>
            </author>
            <author fullname="Alex Bogdanov">
              <organization showOnFrontPage="true">Google, Inc.</organization>
            </author>
            <author fullname="Paul Mattes">
              <organization showOnFrontPage="true">Microsoft</organization>
            </author>
            <date month="July" day="24" year="2022"/>
            <abstract>
              <t indent="0">   Segment Routing (SR) allows a headend node to steer a packet flow
   along any path.  Intermediate per-flow states are eliminated thanks
   to source routing.  The headend node steers a flow into an SR Policy.
   The header of a packet steered in an SR Policy is augmented with an
   ordered list of segments associated with that SR Policy.  This
   document details the concepts of SR Policy and steering into an SR
   Policy.

              </t>
            </abstract>
          </front>
          <seriesInfo name="STD" value="54"/>
          <seriesInfo name="RFC" value="9256"/>
          <seriesInfo name="DOI" value="10.17487/RFC9256"/>
        </reference>

<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.3209.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4552.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5286.xml"/>
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<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5714.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7166.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7474.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7855.xml"/>
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<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8920.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9256.xml"/>

      </references>
    </references>
    <section numbered="false" toc="include" removeInRFC="false" pn="section-appendix.a">
      <name slugifiedName="name-acknowledgments">Acknowledgments</name>
      <t indent="0" pn="section-appendix.a-1"> RFC 8920 included the numbered="false">
      <name>Acknowledgments</name>
      <t>The following acknowledgments:</t>
      <t indent="0" pn="section-appendix.a-2">Thanks acknowledgments are included in <xref target="RFC8920"/>:</t>
      <t>Thanks to <contact fullname="Chris Bowers"/> for his review and comments.</t>
      <t indent="0" pn="section-appendix.a-3">Thanks
      <t>Thanks to <contact fullname="Alvaro Retana"/> for his detailed review and comments.</t>
      <t indent="0" pn="section-appendix.a-4"> For the new version,
      <t>For this document, the authors would like to thank
      <contact fullname="Bruno Decraene"/>.</t>
    </section>
    <section anchor="CONTR" numbered="false" toc="include" removeInRFC="false" pn="section-appendix.b">
      <name slugifiedName="name-contributors">Contributors</name>
      <t indent="0" pn="section-appendix.b-1">The numbered="false">
      <name>Contributors</name>
      <t>The following people contributed to the content
      of this document and should be considered as coauthors:</t>
      <contact fullname="Acee Lindem">
        <organization showOnFrontPage="true">Cisco Systems</organization>
        <organization>LabN Consulting, L.L.C.</organization>
        <address>
          <postal>
          <street/>
          <city/>
          <region/>
          <code/>
            <country>United States of America</country>
          </postal>
          <email>acee@cisco.com</email>
          <email>acee.ietf@gmail.com</email>
        </address>
      </contact>
      <contact fullname="Ketan Talaulikar">
        <organization showOnFrontPage="true">Arrcus, Inc.</organization>
        <organization>Cisco Systems</organization>
        <address>
          <postal>
            <country>India</country>
          </postal>
          <email>ketant.ietf@gmail.com</email>
        </address>
      </contact>
      <contact fullname="Hannes Gredler">
        <organization showOnFrontPage="true">RtBrick
        <organization>RtBrick Inc.</organization>
        <address>
          <postal>
            <country/>
          </postal>
          <email>hannes@rtbrick.com</email>
        </address>
      </contact>
    </section>
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      <name slugifiedName="name-authors-addresses">Authors' Addresses</name>
      <author fullname="Peter Psenak" initials="P." role="editor" surname="Psenak">
        <organization showOnFrontPage="true">Cisco Systems</organization>
        <address>
          <postal>
          <street/>
          <city/>
          <region/>
          <code/>
          <country>Slovakia</country>
          </postal>
          <email>ppsenak@cisco.com</email>
        </address>
      </author>
      <author initials="L." surname="Ginsberg" fullname="Les Ginsberg">
        <organization showOnFrontPage="true">Cisco Systems</organization>
        <address>
          <postal>
          <street/>
          <city/>
          <region/>
          <code/>
          <country>United States of America</country>
          </postal>
          <email>ginsberg@cisco.com</email>
        </address>
      </author>
      <author initials="W." surname="Henderickx" fullname="Wim Henderickx">
        <organization showOnFrontPage="true">Nokia</organization>
        <address>
          <postal>
            <street>Copernicuslaan 50</street>
            <city>Antwerp</city>
            <country>Belgium</country>
            <code>2018 94089</code>
          </postal>
          <email>wim.henderickx@nokia.com</email>
        </address>
      </author>
      <author fullname="Jeff Tantsura" initials="J." surname="Tantsura">
        <organization showOnFrontPage="true">Nvidia</organization>
        <address>
          <postal>
            <street/>
            <city/>
            <region/>
            <code/>
            <country>United States of America</country>
          </postal>
          <email>jefftant.ietf@gmail.com</email>
        </address>
      </author>
      <author fullname="John Drake" initials="J." surname="Drake">
        <organization showOnFrontPage="true">Juniper Networks</organization>
        <address>
          <postal>
          <street/>
          <city/>
          <region/>
          <code/>
          <country>United States of America</country>
          </postal>
          <email>jdrake@juniper.net</email>
        </address>
      </author>
    </section>
  </back>
</rfc>