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<rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902" docName="draft-ietf-pce-local-protection-enforcement-11" number="9488" submissionType="IETF" category="std" updates="5440"> consensus="true" updates="5440" obsoletes="" xml:lang="en" tocInclude="true" sortRefs="true" symRefs="true" version="3">

  <front>
    <title abbrev="Protection Enforcement">Local abbrev="Local Protection Enforcement in PCEP</title> PCEP">Local Protection Enforcement in the Path Computation Element Communication Protocol (PCEP)</title>
    <seriesInfo name="RFC" value="9488"/>
    <author fullname="Andrew Stone" initials="A." surname="Stone">
      <organization>Nokia</organization>
      <address>
        <postal>
          <street>600 March Road</street>
          <city>Kanata</city>
          <region>Ontario</region>
          <code>K2K 2T6</code>
          <country>Canada</country>
        </postal>
        <email>andrew.stone@nokia.com</email>
      </address>
    </author>
    <author fullname="Mustapha Aissaoui" initials="M." surname="Aissaoui">
      <organization>Nokia</organization>
      <address>
        <postal>
          <street>600 March Road</street>
          <city>Kanata</city>
          <region>Ontario</region>
          <code>K2K 2T6</code>
          <country>Canada</country>
        </postal>
        <email>mustapha.aissaoui@nokia.com</email>
      </address>
    </author>
    <author fullname="Samuel Sidor" initials="S." surname="Sidor">
      <organization>Cisco Systems, Inc.</organization>
      <address>
        <postal>
                    <street>Eurovea
          <extaddr>Eurovea Central 3.</street> 3</extaddr>
          <street>Pribinova 10</street>
          <city>Bratislava</city>
          <code>811 09</code>
          <country>Slovakia</country>
        </postal>
        <email>ssidor@cisco.com</email>
      </address>
    </author>
    <author fullname="Siva Sivabalan" initials="S." surname="Sivabalan">
      <organization>Ciena Coroporation</organization> Corporation</organization>
      <address>
        <postal>
          <street>385 Terry Fox Drive</street>
          <city>Kanata</city>
          <region>Ontario</region>
          <code>K2K 0L1</code>
          <country>Canada</country>
        </postal>
        <email>ssivabal@ciena.com</email>
      </address>
    </author>
    <date year="2023" month="June" day="23"/> month="October"/>
    <area>rtg</area>
    <workgroup>pce</workgroup>

<keyword>segment routing</keyword>
<keyword>adjacency sid</keyword>
<keyword>sla</keyword>
<keyword>fast reroute</keyword>
<keyword>ti-lfa</keyword>

      <abstract>
      <t>This document updates RFC5440 RFC 5440 to clarify usage of the local protection desired Local Protection Desired bit signalled signaled in the Path Computation Element Communication Protocol (PCEP).
                This document also introduces a new flag for signalling signaling protection strictness enforcement in PCEP.</t>
    </abstract>
  </front>
  <middle>
    <section title="Introduction" anchor="introduction" toc="default"> toc="default" numbered="true">
      <name>Introduction</name>
      <t>The Path Computation Element (PCE) Communication Protocol (PCEP) <xref target="RFC5440" /> format="default"/> enables the communication between a Path Computation Client (PCC) and a PCE, PCE or between two PCEs based on the PCE architecture <xref target="RFC4655" />. format="default"/>. </t>

      <t>PCEP <xref target="RFC5440" /> format="default"/> utilizes flags, values
      values, and concepts previously defined in RSVP-TE Extensions <xref
      target="RFC3209" /> format="default"/> and Fast Reroute Extensions to
      RSVP-TE <xref target="RFC4090" />. format="default"/>.  One such concept in
      PCEP is the 'Local Local Protection Desired' (L Desired (L) flag in the LSPA Object LSP
      Attributes (LSPA) object in <xref target="RFC5440" />), format="default"/>, which
      was originally defined in the SESSION-ATTRIBUTE Object Session Attribute object in RFC3209. <xref
      target="RFC3209" format="default"/>. In RSVP, this flag signals to
      downstream routers that they may use a local repair mechanism.  The
      headend router calculating the path does not know whether if a downstream
      router will or will not protect a hop during its calculation.
      Therefore, a local protection desired the L flag does not require the transit
      router to satisfy protection in order to establish the RSVP signalled RSVP-signaled
      path.  This flag is signalled signaled in PCEP as an attribute of the LSP Label Switched Path (LSP) via the LSP Attributes
      LSPA object. </t>
      <t>PCEP Extensions for Segment Routing (<xref <xref target="RFC8664" />)
      format="default"/> extends support in PCEP for Segment Routed Routing paths. The
      path list is encoded with Segment Identifiers, Identifiers (SIDs), each of which
      might offer local protection.  The PCE may discover the protection
      eligibility for a Segment Identifier (SID) SID via BGP-LS the Border Gateway Protocol - Link State (BGP-LS)
      <xref target="RFC9085" /> format="default"/> and take the protection into
      consideration as a path constraint.
      </t>
      <t>It is desirable for an operator to be able to define the enforcement, or strictness enforcement of the protection requirement. </t>
      <t>This document updates <xref target="RFC5440" /> format="default"/> by further describing the behaviour with behavior of the Local Protection Desired Flag (L flag) (L) flag and extends on it with the introduction of the Protection Enforcement Flag (E flag).</t> (E) flag.</t>

      <t>The document contains reference notes for descriptions in the context of Segment Routing, however Routing; however, the content described is agnostic in regard to path setup type and data plane technology agnostic.</t> technology.</t>
    </section>
    <section title="Requirements Language" anchor="requirements-language">
            <t>The anchor="requirements-language" numbered="true" toc="default">
      <name>Requirements Language</name>
        <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" format="default" sectionFormat="of" derivedContent="RFC2119"/> <xref target="RFC8174" format="default" sectionFormat="of" derivedContent="RFC8174"/> target="RFC2119"/> <xref target="RFC8174"/>
    when, and only when, they appear in all capitals, as shown here.</t> here.
        </t>
    </section>
    <section title="Terminology" anchor="terminology"> anchor="terminology" numbered="true" toc="default">
      <name>Terminology</name>
      <t>This document uses the following terminology:</t>
            <t>   PROTECTION MANDATORY: The Path MUST
<dl newline="false" spacing="normal">
      <dt>PROTECTION MANDATORY:</dt><dd>The path <bcp14>MUST</bcp14> have protection eligibility on all links.</t>
            <t>   UNPROTECTED MANDATORY: The Path MUST NOT links.</dd>
      <dt>UNPROTECTED MANDATORY:</dt><dd>The path <bcp14>MUST NOT</bcp14> have protection eligibility on all links.</t>
            <t>   PROTECTION PREFERRED: The Path links.</dd>
      <dt>PROTECTION PREFERRED:</dt><dd>The path should have protection eligibility on all links but might contain links which that do not have protection eligibility.</t>
            <t>   UNPROTECTED PREFERRED: The Path eligibility.</dd>
      <dt>UNPROTECTED PREFERRED:</dt><dd>The path should not have protection eligibility on all links but might contain links which that have protection eligibility.</t>
            <t>   PCC:  Path eligibility.</dd>
      <dt>PCC:</dt><dd>Path Computation Client.  Any client application requesting a
                path computation to be performed by a Path Computation Element.</t>
            <t>   PCE:  Path Element.</dd>
      <dt>PCE:</dt><dd>Path Computation Element.  An entity (component, application,
                or network node) that is capable of computing a network path or
                route based on a network graph and applying computational
                constraints.</t>
            <t>   PCEP:  Path
                constraints.</dd>
      <dt>PCEP:</dt><dd>Path Computation Element Protocol.</t>
            <t>   LSPA: LSP Communication Protocol</dd>
      <dt>LSPA:</dt><dd>LSP Attributes Object in PCEP, defined in RFC5440</t> object <xref target="RFC5440" format="default"/></dd>
</dl>
    </section>
    <section title="Motivation" anchor="motivation" toc="default"> toc="default" numbered="true">
      <name>Motivation</name>
      <section title="Implementation differences" anchor="implementation-differences" toc="default"> toc="default" numbered="true">
        <name>Implementation Differences</name>

      <t>As defined in <xref target="RFC5440" /> format="default"/>, the mechanism to signal protection enforcement in PCEP is the previously mentioned L flag defined in the LSPA Object. object.
                    The name of the flag uses the term "Desired", which by definition means "strongly wished for or intended" and the intended". The use case for this flag originated from the in RSVP.
                    For RSVP signalled RSVP-signaled paths, local protection is not within control of the PCE. However, <xref target="RFC5440" /> format="default"/> does state "When that "[w]hen set, this means that the computed path must include links protected with Fast Reroute as defined in [RFC4090]." <xref target="RFC4090" />."
                    Implementations of that use PCEP <xref target="RFC5440" /> format="default"/> have either interpreted the L flag as either PROTECTION MANDATORY or PROTECTION PREFERRED, leading to operational differences. </t>
      </section>
      <section title="SLA Enforcement" anchor="sla-enforcement" toc="default"> toc="default" numbered="true">
        <name>SLA Enforcement</name>

          <t> The boolean bit L flag is a boolean bit and thus unable to distinguish between the different
            options of PROTECTION MANDATORY, UNPROTECTED MANDATORY, PROTECTION PREFERRED
            PREFERRED, and UNPROTECTED PREFERRED.
                    Selecting one of the these options is typically dependent on the service
                    level agreement Service
                    Level Agreement (SLA) the operator wishes to impose on the LSP. A network
                    may be providing transit to multiple service agreement SLA definitions against
                    the same base topology network, whose behavior could vary, such as
                    wanting local protection to be invoked on some LSPs and not wanting
                    local protection on others. When enforcement is used, the resulting shortest path calculation is impacted.</t>

		    <t> For example, PROTECTION MANDATORY is for use cases where in which an operator may need the LSP to follow a path which that has local protection provided along the full path, ensuring that
                    traffic will be fast rerouted at the point if there is a failure anywhere along the path that traffic will be fast re-routed at the point. path. </t>

		    <t> For As another example, UNPROTECTED MANDATORY is when for use cases in which an operator may
                    intentionally prefer an LSP to not be locally protected, protected
                    and thus would rather local failures cause the LSP to go down.
                    An example scenario is one where an LSP is protected with
                    path protection via a secondary diverse LSP.
                    Each LSP is traffic engineered to follow specific traffic engineered traffic-engineered criteria
                    computed by the PCE to satisfy the SLA. Upon a failure, if local protection
                    is invoked on the active LSP traffic, the traffic may temporarily
                    traverse links which that violate the TE requirements and could negatively
                    impact the resources being traversed (e.g., insufficient bandwidth).
                    In addition, depending on the network topological scenario,
                    it may be not be feasible for the PCE to reroute the LSP while
                    respecting the TE requirements requirements, which include path diversity,
                    resulting diversity; this results
                    in the LSP being torn down and switched to the
                    protected path anyways. In such scenarios its scenarios, it is desirable for
                    the LSP to be simply torn down immediately and not re-routed rerouted
                    through local protection, so that traffic
                    may be forwarded through an already established already-established
                    traffic-engineered secondary path. </t>
        <t>
                    Both the UNPROTECTED PREFERRED and PROTECTED PREFERRED options provide a relaxation of the protection constraint.
                    These options can be used when an operator does not require protection enforcement. Regardless of the option selected, the protection status of a
                    resource does not influence whether the link must be pruned during a path calculation. Furthermore, the selection of either option indicates a priority selection to the
                    PCE when there is an option to choose a protected or unprotected instruction associated with a resource, ensuring consistent PCE behavior across different implementations.
        </t>
        <t>When used with Segment Routing, an adjacency may have both a protected SID and an unprotected SID.
                    If the UNPROTECTED PREFERRED option is selected, the PCE chooses the unprotected SID. Alternatively, if the PROTECTED PREFERRED option is selected, the PCE chooses the protected SID SID.
        </t>
      </section>
    </section>
    <section title="Protection anchor="protection-enforcement-flag--e-flag-" toc="default" numbered="true">
      <name>Protection Enforcement Flag (E flag)" anchor="protection-enforcement-flag--e-flag-" toc="default">
            <t>Section 7.11 in Path Computation Element Protocol <xref Flag)</name>
      <t><xref target="RFC5440" /> section="7.11" sectionFormat="of"></xref> describes the encoding of the Local Protection Desired (L flag).
                A (L) flag.
                The Protection Enforcement flag "E" is specified below, extending (E) flag, which extends the L flag.</t>
            <t>[RFC Editor Note: The text below assumes the E bit remains the early allocation value 6. Please adjust if this changes and remove this note before publication.]</t>
            <figure>
                <artwork><![CDATA[Codespace flag, is specified below.</t>
		<table anchor="flagfieldtable" align="left">
  <name>Codespace of the Flag field Field (LSPA Object)

     Bit      Description                      Reference

      7    Local Protection Desired             RFC5440

      6    Local Object)</name>
  <thead>
    <tr>
      <th>Bit</th>
      <th>Description</th>
      <th>Reference</th>
    </tr>
  </thead>
  <tbody>
      <tr>
          <td>6</td>
          <td>Protection Enforcement</td>
          <td>RFC 9488</td>
      </tr>
    <tr>
      <td>7</td>
      <td>Local Protection Enforcement        This document]]></artwork>
            </figure> Desired</td>
      <td>RFC 5440</td>
    </tr>
  </tbody>
</table>

      <t>The following shows the format of the LSPA Object object as defined in <xref target="RFC5440" /> is:</t>
            <figure>
                <artwork><![CDATA[ format="default"/> with the addition of the E flag defined in this document:</t>
      <artwork name="" type="" align="left" alt=""><![CDATA[
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Exclude-any                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Include-any                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Include-all                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Setup Prio   |  Holding Prio |     Flags |E|L|   Reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                     Optional TLVs                           //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
            </figure>
            <t>   Flags
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>

      <dl newline="true" spacing="normal">
	<dt>Flags (8 bits)</t>
            <t>
                <list style="symbols">
                    <t>
                        L Flag: As bits):</dt><dd>
	<dl newline="false" spacing="normal">
<dt>L (Local Protection Desired):</dt><dd>This flag is defined in <xref target="RFC5440" /> format="default"/>
and further updated by this document. When set to 1, protection is
desired. When set to 0, protection is not desired. The enforcement of the
protection is identified via the E flag.
                    </t>
                    <t>E Flag flag.</dd>
<dt>E (Protection Enforcement): This Enforcement):</dt><dd>This flag controls the strictness in
with which the PCE must apply the L flag.  When set to 1, the value of the L
flag needs to be respected during resource selection by the PCE.  When the E flag
is set to 0, an attempt to respect the value of the L flag is made; however,
the PCE could relax or ignore the L flag when computing a path.  The
statements below indicate preference when the E flag is set to 0 in
combination with the L flag value.</t>
                </list>
            </t> value.
</dd>
	</dl>
      </dd>
      </dl>

      <t>When both the L flag and E flag are set to 1, then the PCE MUST <bcp14>MUST</bcp14> consider the protection eligibility as a PROTECTION MANDATORY constraint.</t>
      <t>When the L flag is set to 1 and the E flag is set to 0, then the PCE MUST <bcp14>MUST</bcp14> consider the protection eligibility as a PROTECTION PREFERRED constraint.</t>
      <t>  When both the L flag and E flag are set to 0, then the PCE SHOULD <bcp14>SHOULD</bcp14>
                consider the protection eligibility as an UNPROTECTED PREFERRED
                constraint but MAY <bcp14>MAY</bcp14> consider the protection eligibility as an UNPROTECTED
                MANDATORY constraint. An example of when the latter behavior might
                be chosen is if the PCE has some means (outside the scope of this
                document) to detect that it is interacting with a legacy PCC that expects
                the legacy behavior.</t>
      <t>When the L flag is set to 0 and the E flag is set to 1, then the PCE MUST <bcp14>MUST</bcp14> consider the protection eligibility as an UNPROTECTED MANDATORY constraint.</t>
      <t>
                If a PCE is unable to infer the protection status of a resource, the PCE MAY <bcp14>MAY</bcp14> use local policy to define protected status assumptions.

                When computing a Segment Routed Routing path, It it is RECOMMENDED <bcp14>RECOMMENDED</bcp14> that a PCE assume a Node SID is protected. It is also RECOMMENDED <bcp14>RECOMMENDED</bcp14> that a PCE assume an Adjacency SID is protected if the backup flag advertised with the Adjacency SID is set.
      </t>
      <section title="Backwards Compatibility" anchor="compatibility" toc="default">

                <t>Considerations toc="default" numbered="true">
        <name>Backwards Compatibility</name>
        <t>This section outlines considerations for the E flag bit in the message
            passing between the PCC and the PCE for the E flag bit which that are not supported by the entity are outlined in this section, with entity.
            The requirements for the PCE and the PCC implementing this document are described
            at the end.</t>
        <t>For a PCC or PCE which that does not yet support this document, the E flag is ignored and set to zero 0 in PCRpt and/or PCUpd messages as per <xref target="RFC5440" /> format="default"/> for PCC-initiated LSPs or as per <xref target="RFC8281" /> format="default"/> for PCE-initiated LSPs. It is important to note that <xref target="RFC8231" /> format="default"/> and <xref target="RFC8281" /> format="default"/> permit the LSP Attribute Object LSPA object <xref target="RFC5440" format="default"/> to be included in PCUpd messages for PCC-initiated and PCE-initiated LSPs.
        </t>
        <t>
            For PCC-initiated LSPs, PCUpd the E flag (and L flag) in a PCUpd message is an echo from the
            previous PCRpt however message; however, the bit value is ignored on the PCE from the
            previous PCRpt, therefore PCRpt message, so the E flag value set in the PCUpd message is zero. 0.
                    A PCE which that does not support this document sends PCUpd messages with the E flag set to 0 for PCC-initated PCC-initiated LSPs even if set to 1 in the prior PCReq or PCRpt. PCRpt message.
        </t>
        <t>
                    A PCC which that does not support this document sends PCRpt messages with the E flag set to 0 for PCE-initiated LSPs even if set to 1 in the prior PCInitiate or PCUpd. PCUpd message.
        </t>
        <t>For a PCC which that does support this document, it MAY set the E flag <bcp14>MAY</bcp14> be set to 1 depending on local configuration.
                    If communicating with a PCE which that does not yet support this document, the PCE follows the behaviour behavior specified in <xref target="RFC5440" /> format="default"/> and will ignore ignores the E flag.
                    Thus, a computed path might not respect the enforcement constraint.</t>
        <t>For PCC-initiated LSPs, the PCC SHOULD <bcp14>SHOULD</bcp14> ignore the E flag value received from the PCE in a PCUpd message as it may be communicating with a PCE which that does not support this document.</t>
        <t>For PCE-initiated LSPs, the PCC MAY <bcp14>MAY</bcp14> process the E flag value received from the PCE in a PCUpd message. The PCE SHOULD <bcp14>SHOULD</bcp14> ignore the E flag value received from the PCC in a PCRpt message as it may be communicating with a PCC
                which
                that does not support this document. </t>
      </section>
    </section>
    <section anchor="Imp" title="Implementation Status" toc="default">
            <t>[Note to the RFC Editor - remove this section before publication, as well as remove the reference to RFC 7942.]</t>
            <t>This section records the status of known implementations of the
                protocol defined by this specification at the time of posting of
                this Internet-Draft, and is based on a proposal described in
                <xref target="RFC7942"/>.  The description of implementations in this section is
                intended to assist the IETF in its decision processes in
                progressing drafts to RFCs.  Please note that the listing of any
                individual implementation here does not imply endorsement by the
                IETF.  Furthermore, no effort has been spent to verify the
                information presented here that was supplied by IETF contributors.
                This is not intended as, and must not be construed to be, a
                catalogue of available implementations or their features.  Readers
                are advised to note that other implementations may exist.</t>

            <t>According to <xref target="RFC7942"/>, "this will allow reviewers and working
                groups to assign due consideration to documents that have the
                benefit of running code, which may serve as evidence of valuable
                experimentation and feedback that have made the implemented
                protocols more mature.  It is up to the individual working groups
                to use this information as they see fit".</t>

            <section title="Nokia Implementation" toc="default">
                <t>
                    <list style="symbols">
                        <t>Organization: Nokia</t>
                        <t>Implementation: NSP PCE and SROS PCC.</t>
                        <t>Description: Implementation for calculation and conveying intention described in this document</t>
                        <t>Maturity Level: Demo</t>
                        <t>Coverage: Full</t>
                        <t>Contact: andrew.stone@nokia.com </t>
                    </list>
                </t>
            </section>

            <section title="Cisco Implementation" toc="default">
                <t>
                    <list style="symbols">
                        <t>Organization: Cisco Systems, Inc.</t>
                        <t>Implementation: IOS-XR PCE and PCC.</t>
                        <t>Description: Implementation for calculation and conveying intention described in this document</t>
                        <t>Maturity Level: Demo</t>
                        <t>Coverage: Full</t>
                        <t>Contact: ssidor@cisco.com </t>
                    </list>
                </t>
            </section>
        </section>

        <section title="Security Considerations" anchor="security-considerations" toc="default"> toc="default" numbered="true">
      <name>Security Considerations</name>
      <t>This document clarifies the behaviour behavior of an existing flag and introduces a new flag to provide further control of that existing behaviour. behavior. The introduction of this new flag and behaviour the behavior clarification does do not create any new sensitive information. No additional security measure is required.</t>
      <t>Securing the PCEP session using Transport Layer Security (TLS) <xref target="RFC8253" />, format="default"/>, as per the recommendations and best current practices in <xref target="RFC9325" /> format="default"/>, is RECOMMENDED.</t> <bcp14>RECOMMENDED</bcp14>.</t>
    </section>
    <section title="IANA Considerations" anchor="iana-considerations" toc="default">
                <t>[RFC Editor Note: The text below assumes the E bit remains the early allocation value 6. Please adjust if this changes and remove this note before publication.]</t> toc="default" numbered="true">
      <name>IANA Considerations</name>
      <t>This document defines a new bit value in the sub-registry subregistry "LSPA Object Flag Field" in the "Path Computation Element Protocol (PCEP) Numbers" registry. IANA has made the following codepoint allocation.</t>
                <figure>
                    <artwork>
                        <![CDATA[
            Bit    Name                         Reference

             6     Protection Enforcement       This document]]>
                    </artwork>
                </figure>

<table anchor="prot-enforce-iana-table" align="left">
  <name>Addition to LSPA Object Flag Field Registry</name>
  <thead>
    <tr>
      <th>Bit</th>
      <th>Description</th>
      <th>Reference</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>6</td>
      <td>Protection Enforcement</td>
      <td>RFC 9488</td>
    </tr>
  </tbody>
</table>

    </section>
  </middle>
  <back>
        <references title="Normative References">
            <?rfc include="reference.RFC.2119.xml" ?>
            <?rfc include="reference.RFC.8174.xml" ?>
            <?rfc include="reference.RFC.5440.xml" ?>
            <?rfc include="reference.RFC.3209.xml" ?>
            <?rfc include="reference.RFC.4090.xml" ?>
            <?rfc include="reference.RFC.8253.xml" ?>
            <?rfc include="reference.RFC.8231.xml" ?>
            <?rfc include="reference.RFC.8281.xml" ?>
            <?rfc include="reference.RFC.9325.xml" ?>

    <references>
      <name>References</name>
      <references>
        <name>Normative References</name>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5440.xml"/>
        <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.4090.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8253.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8231.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8281.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9325.xml"/>
      </references>
      <references>
        <name>Informative References</name>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4655.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8664.xml"/>
        <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9085.xml"/>
      </references>

        <references title="Informative References">
            <?rfc include="reference.RFC.4655.xml" ?>
            <?rfc include="reference.RFC.7942.xml" ?>
            <?rfc include="reference.RFC.8664.xml" ?>
            <?rfc include="reference.RFC.9085.xml" ?>
    </references>
    <section title="Acknowledgements" anchor="Acknowledgements" numbered="false" toc="default">
      <name>Acknowledgements</name>
      <t>Thanks to Dhruv Dhody, Mike Koldychev, and John Scudder <contact fullname="Dhruv Dhody"/>, <contact fullname="Mike Koldychev"/>, and <contact fullname="John Scudder"/> for reviewing and providing very valuable feedback and discussions on this document.</t>
      <t>Thanks to Julien Meuric <contact fullname="Julien Meuric"/> for shepherding this document. </t>
    </section>
  </back>
</rfc>