<?xmlversion="1.0" encoding="US-ASCII"?>version='1.0' encoding='UTF-8'?> <!-- [rfced] Because this document updates RFC 9350, please review the errata reported for RFC 9350 (https://www.rfc-editor.org/errata/rfc9350) and let us know if you confirm our opinion that none of them are relevant to the content of this document. --> <!--[rfced] FYI, we have added RFC 9843 to the list of updated documents in the header, based on the statement in the abstract. --> <!DOCTYPE rfcSYSTEM "rfc2629.dtd"> <?rfc toc="yes"?> <?rfc tocompact="yes"?> <?rfc tocdepth="3"?> <?rfc tocindent="yes"?> <?rfc symrefs="yes"?> <?rfc sortrefs="yes"?> <?rfc comments="yes"?> <?rfc inline="yes"?> <?rfc compact="yes"?> <?rfc subcompact="no"?>[ <!ENTITY nbsp " "> <!ENTITY zwsp "​"> <!ENTITY nbhy "‑"> <!ENTITY wj "⁠"> ]> <rfc xmlns:xi="http://www.w3.org/2001/XInclude" category="std" docName="draft-ietf-lsr-igp-flex-algo-reverse-affinity-12" number="9917" consensus="true" ipr="trust200902"updates="9350">updates="9350, 9843" obsoletes="" submissionType="IETF" xml:lang="en" tocInclude="true" tocDepth="3" symRefs="true" sortRefs="true" version="3"> <front> <title abbrev="Flex-Algorithm Reverse Affinity">IGP Flexible Algorithms Reverse Affinity Constraint</title> <seriesInfo name="RFC" value="9917"/> <author fullname="Peter Psenak" initials="P." surname="Psenak"> <organization>Cisco Systems</organization> <address> <postal> <street>Apollo Business Center</street> <street>Mlynske nivy 43</street> <city>Bratislava</city> <code>82109</code> <country>Slovakia</country> </postal> <email>ppsenak@cisco.com</email> </address> </author> <author fullname="Jakub Horn" initials="J." surname="Horn"> <organization>Cisco Systems</organization> <address> <postal><street></street><city>Milpitas</city> <code>95035</code> <region>CA</region><country>USA</country><country>United States of America</country> </postal> <email>jakuhorn@cisco.com</email> </address> </author> <author fullname="Amit Dhamija" initials="A" surname="Dhamija"> <organization>Arrcus</organization> <address><postal> <street/> </postal><email>amitd@arrcus.com</email> </address> </author><date/> <area>Routing Area</area> <workgroup>LSR Working Group</workgroup> <keyword>IGP</keyword> <keyword>Draft</keyword><date month="January" year="2026"/> <area>RTG</area> <workgroup>lsr</workgroup> <!-- [rfced] Please insert any keywords (beyond those that appear in the title) for use on https://www.rfc-editor.org/search. --> <keyword>example</keyword> <!--[rfced] Because of the abstract's length, we suggest moving some of its content, particularly the second paragraph, to the Introduction. As noted in Section 4.3 of RFC 7322: Every RFC must have an Abstract that provides a concise and comprehensive overview of the purpose and contents of the entire document, to give a technically knowledgeable reader a general overview of the function of the document.... A satisfactory Abstract can often be constructed in part from material within the Introduction section, but an effective Abstract may be shorter, less detailed, and perhaps broader in scope than the Introduction. Please let us know how the text may be updated. --> <abstract> <t>An IGP Flexible Algorithm (Flex-Algorithm) enables the computation of constraint-based paths within an IGP domain, allowing operators to influence path selection according to administrative policies. This document defines an extension to Flex-Algorithm that allows the inclusion or exclusion of links from path computation based on Administrative Groups (also known as link affinities) associated with the reverse direction of the path under computation.</t> <t>This extension enhances the path selection capabilities of Flex-Algorithm by enabling reverse-affinity-based constraints, which are particularly useful for scenarios where path symmetry or directional link attributes are operationally significant.</t> <t>This document updates<xref target="RFC9350"/>RFCs 9350 and<xref target="I-D.ietf-lsr-flex-algo-bw-con"/>9843 by introducing the new IANA registry that specifies the ordered set of rules that are used to prune links from the topology during the Flex-Algorithm path computation.</t> </abstract> </front> <middle> <sectiontitle="Introduction">numbered="true" toc="default"> <name>Introduction</name> <t>IGP protocols historically computed the best paths over the network solely based on the IGP metric assigned to the links. An IGP Flex-Algorithm as specified in <xreftarget="RFC9350"/>target="RFC9350" format="default"/> allows IGPs to compute constraint-based paths. Several mechanisms to include or exclude the link during the Flex-Algorithm path calculation have been defined already:<list style="hanging"> <t> - link</t> <ul spacing="normal"> <li>link inclusion or exclusion based on the presence of a specific Admin Group(s)-<xreftarget="RFC9350"/></t> <t> - linktarget="RFC9350" format="default"/></li> <li>link exclusion based on the presence of a specific Shared Risk Link Group (SRLG)-<xreftarget="RFC9350"/></t> <t> - linktarget="RFC9350" format="default"/></li> <li>link exclusion based on minimum bandwidth-<xreftarget="I-D.ietf-lsr-flex-algo-bw-con"/></t> <t> - linktarget="RFC9843" format="default"/></li> <li>link exclusion based on maximum delay-<xreftarget="I-D.ietf-lsr-flex-algo-bw-con"/></t> </list></t>target="RFC9843" format="default"/></li> </ul> <!--[rfced] FYI, in addition to expanding "SPF", the word "path" was removed here to match usage of "SPF computation" in this document and other RFCs. Please let us know if you prefer otherwise. Original: the SPF path computation Current: the Shortest Path First (SPF) computation --> <t>This document extends IGP Flex-Algorithm with additional constraints for inclusion or exclusion of links in the path based on Admin Groups associated with the reverse direction of theSPF pathShortest Path First (SPF) computation.</t> <t>This document updates <xreftarget="RFC9350"/>target="RFC9350" format="default"/> and <xreftarget="I-D.ietf-lsr-flex-algo-bw-con"/>target="RFC9843" format="default"/> by creating the new IANA registry that specifies the ordered set of rules that are used to prune links from the topology during the Flex-Algorithm path computation (refer to <xreftarget="NEW_REG"/>).</t>target="NEW_REG" format="default"/>).</t> <t>The term OSPF in this document is used to cover both OSPFv2 and OSPFv3 protocols.</t> </section> <section anchor="ReqLang"title="Requirements Language"> <t>Thenumbered="true" toc="default"> <name>Requirements Language</name> <t> The key words"MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY","<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>", "<bcp14>MAY</bcp14>", and"OPTIONAL""<bcp14>OPTIONAL</bcp14>" in this document are to be interpreted as described in BCP 14 <xreftarget="RFC2119">BCP 14</xref>target="RFC2119"/> <xref target="RFC8174"/> when, and only when, they appear in all capitals, as shownhere.</t>here. </t> </section> <sectiontitle="Usenumbered="true" toc="default"> <name>Use CaseExample">Example</name> <t>The Flexible AlgorithmdefinitionDefinition (FAD) can specify Extended Administrative Groups that are used by the operator to include or exclude links during the Flex-Algorithm path computation <xreftarget="RFC9350"/>.target="RFC9350" format="default"/>. These link Extended Administrative Groups are checked in the path direction of the SPF computation, e.g., in the direction from the root vertex towardverticiesvertices of increasing distance.</t> <t>In certain scenarios, it is beneficial to evaluate the Extended Administrative Groups associated with the reverse direction of a link, rather than solely those in the direction of path computation. Consider a point-to-point link represented as a pair of directed edges between two nodes, A and B. When computing a path from A to B, issues such as input errors on the link, detectable only at the receiving node B, may be operationally significant. An operator might monitor metrics likeCRCCyclic Redundancy Check (CRC) errors or other input-related faults at node B and apply thresholds over a defined observation period. If such a threshold is exceeded, node B may locally assign specific Extended Administrative Groups to the link in the direction from B to A.</t> <t>To accommodate this operational intent, the Flex-Algorithm can be extended to inspect the Extended Administrative Groups of the reverse-direction edge (from B to A) when evaluating the forward-direction edge (from A to B) during path computation. This enables the exclusion of links from the computed topology based on conditions detected at the far end of the link, improving network reliability and policy control.</t> </section> <sectiontitle="Deployment Consideration"> <t>Threshold basednumbered="true" toc="default"> <name>Deployment Consideration</name> <t>Threshold-based setting of the link Extended Administrative Groups must be done with care to avoid excessive flooding and constant Flex-Algorithm pathre-calculation.</t>recalculation.</t> <t>One possible approach is to use two different thresholds when setting andun-settingunsetting the Extended Administrative Group on the link. For example, when setting the Extended Administrative Group on the link based on the percentage of certain incoming errors, higher threshold is used for setting and lower threshold is used forun-settingunsetting the Extended Administrative Group on the link.</t> <!--[rfced] To avoid the repetition of "Usage" and "use" to improve readability, may we update "Usage" to "Application"? Original: Usage of such throttling mechanism can also be used to avoid frequent changes in the setting of the Extended Administrative Group on a link to affect the stability of the receivers. Perhaps: Application of such throttling mechanism can also be used to avoid frequent changes in the setting of the Extended Administrative Group on a link to affect the stability of the receivers. --> <t>Many implementations provide a throttling mechanism that limits the rate at which theLSPLabel Switched Path (LSP) in case ofISIS,IS-IS, orLSALink State Advertisement (LSA) in case of OSPFv2 and OSPFv3, is updated at the originator. Such mechanism is typically not specific to any particular link attribute, but rather considers any change in the LSP or LSA. Usage of such throttling mechanism can also be used to avoid frequent changes in the setting of the Extended Administrative Group on a link to affect the stability of the receivers.</t> </section> <section anchor="ISISFLEXALGEXLTLV"title="IS-ISnumbered="true" toc="default"> <name>IS-IS Flexible Algorithm Exclude Reverse Admin GroupSub-TLV">Sub-TLV</name> <t>The IS-IS Flexible Algorithm Exclude Reverse Admin Group (FAERAG) Sub-TLV is used to advertise the exclude rule that is used during the Flex-Algorithm path calculation as specified in <xreftarget="FLEXALGPATHCALC"/>.target="FLEXALGPATHCALC" format="default"/>. </t> <t>The IS-IS FAERAG Sub-TLV is aSub-TLVsub-TLV of the IS-IS FAD Sub-TLV. It has the following format:<figure> <artwork><![CDATA[</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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extended Admin Group | +- -+ | ... |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: ]]></artwork> </figure> <list style="hanging"> <t>Type+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork> <t>where:</t> <dl newline="false" spacing="normal"> <dt>Type (1octet): 10</t> <t>Lengthoctet):</dt><dd>10</dd> <dt>Length (1octet): Variable,octet):</dt><dd>Variable, dependent on the size of the Extended Admin Group. The lengthMUST<bcp14>MUST</bcp14> be a multiple of 4 octets. If the length is not a multiple of 4 octets, the entireSub-TLV MUSTsub-TLV <bcp14>MUST</bcp14> be ignored by thereceiver.</t> <t>Extendedreceiver.</dd> <dt>Extended AdministrativeGroup: ExtendedGroup:</dt><dd>Extended Administrative Group as defined in <xreftarget="RFC7308"/>.</t> </list></t>target="RFC7308" format="default"/>.</dd> </dl> <t>The IS-IS FAERAG Sub-TLVMUST NOT<bcp14>MUST NOT</bcp14> appear more than once in a single IS-IS FAD Sub-TLV. If it appears more than once, the IS-IS FAD Sub-TLVMUST<bcp14>MUST</bcp14> be ignored by the receiver.</t> <t>The IS-IS FAERAG Sub-TLVMUST NOT<bcp14>MUST NOT</bcp14> appear more than once in the set of FADsub-TLVsSub-TLVs for a given Flex-Algorithm from a given IS. If it appears more than once in such set, the IS-IS FAERAG Sub-TLV in the first occurrence in thelowest numberedlowest-numbered LSP from a given ISMUST<bcp14>MUST</bcp14> be used and any other occurrencesMUST<bcp14>MUST</bcp14> be ignored by the receiver.</t> </section> <section anchor="ISISFLEXALGINCANYTLV"title="IS-ISnumbered="true" toc="default"> <name>IS-IS Flexible Algorithm Include-Any Reverse Admin GroupSub-TLV">Sub-TLV</name> <t>The IS-IS Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV is used to advertise the include-any rule that is used during the Flex-Algorithm path calculation as specified in <xreftarget="FLEXALGPATHCALC"/>.</t>target="FLEXALGPATHCALC" format="default"/>.</t> <t>The format of the IS-IS Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV is identical to the format of the FAERAG Sub-TLV in <xreftarget="ISISFLEXALGEXLTLV"/>.</t>target="ISISFLEXALGEXLTLV" format="default"/>.</t> <t>IANA has assigned Type value of 11 for the IS-IS Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV.</t> <t>The IS-IS Flexible Algorithm Include-Any Reverse Admin Group Sub-TLVMUST NOT<bcp14>MUST NOT</bcp14> appear more than once in a single IS-IS FAD Sub-TLV. If it appears more than once, the IS-IS FAD Sub-TLVMUST<bcp14>MUST</bcp14> be ignored by the receiver.</t> <t>The IS-IS Flexible Algorithm Include-Any Reverse Admin Group Sub-TLVMUST NOT<bcp14>MUST NOT</bcp14> appear more than once in the set of FADsub-TLVsSub-TLVs for a given Flex-Algorithm from a given IS. If it appears more than once in such set, the IS-IS Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV in the first occurrence in thelowest numberedlowest-numbered LSP from a given ISMUST<bcp14>MUST</bcp14> be used and any other occurrencesMUST<bcp14>MUST</bcp14> be ignored by the receiver.</t> </section> <section anchor="ISISFLEXALGINCALLTLV"title="IS-ISnumbered="true" toc="default"> <name>IS-IS Flexible Algorithm Include-All Reverse Admin GroupSub-TLV">Sub-TLV</name> <t>The IS-IS Flexible Algorithm Include-All Reverse Admin Group Sub-TLV is used to advertise the include-all rule that is used during the Flex-Algorithm path calculation as specified in <xreftarget="FLEXALGPATHCALC"/>.</t>target="FLEXALGPATHCALC" format="default"/>.</t> <t>The format of the IS-IS Flexible Algorithm Include-All Reverse Admin Group Sub-TLV is identical to the format of the FAERAG Sub-TLV in <xreftarget="ISISFLEXALGEXLTLV"/>.</t>target="ISISFLEXALGEXLTLV" format="default"/>.</t> <t>IANA has assigned Type value of 12 for the IS-IS Flexible Algorithm Include-All Reverse Admin Group Sub-TLV.</t> <t>The IS-IS Flexible Algorithm Include-All Reverse Admin Group Sub-TLVMUST NOT<bcp14>MUST NOT</bcp14> appear more than once in a single IS-IS FAD Sub-TLV. If it appears more than once, the IS-IS FAD Sub-TLVMUST<bcp14>MUST</bcp14> be ignored by the receiver.</t> <t>The IS-IS Flexible Algorithm Include-All Reverse Admin Group Sub-TLVMUST NOT<bcp14>MUST NOT</bcp14> appear more than once in the set of FADsub-TLVsSub-TLVs for a given Flex-Algorithm from a given IS. If it appears more than once in such set, the IS-IS Flexible Algorithm Include-All Reverse Admin Group Sub-TLV in the first occurrence in thelowest numberedlowest-numbered LSP from a given ISMUST<bcp14>MUST</bcp14> be used and any other occurrencesMUST<bcp14>MUST</bcp14> be ignored by the receiver.</t> </section> <section anchor="OSPFFLEXALGEXLTLV"title="OSPFnumbered="true" toc="default"> <name>OSPF Flexible Algorithm Exclude Reverse Admin GroupSub-TLV">Sub-TLV</name> <t>The OSPF Flexible Algorithm Exclude Reverse Admin Group (FAERAG) Sub-TLV is used to advertise the exclude rule that is used during the Flex-Algorithm path calculation as specified in <xreftarget="FLEXALGPATHCALC"/>.target="FLEXALGPATHCALC" format="default"/>. </t> <t>The OSPF FAERAG Sub-TLV is aSub-TLVsub-TLV of the OSPF FAD TLV. It has the following format:<figure> <artwork><![CDATA[</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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extended Admin Group | +- -+ | ... |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: ]]></artwork> </figure> <list style="hanging"> <t>Type+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork> <t>where:</t> <dl newline="false" spacing="normal"> <dt>Type (2octets): 10</t> <t>Lengthoctets):</dt><dd>10</dd> <dt>Length (2octets): Variable,octets):</dt><dd>Variable, dependent on the size of the Extended Admin Group. The lengthMUST<bcp14>MUST</bcp14> be a multiple of 4 octets. If the length is not a multiple of 4 octets, the entireSub-TLV MUSTsub-TLV <bcp14>MUST</bcp14> be ignored by thereceiver.</t> <t>Extendedreceiver.</dd> <dt>Extended AdministrativeGroup: ExtendedGroup:</dt><dd>Extended Administrative Group as defined in <xreftarget="RFC7308"/>.</t> </list></t>target="RFC7308" format="default"/>.</dd> </dl> <t>The OSPF FAERAG Sub-TLVMUST NOT<bcp14>MUST NOT</bcp14> appear more than once in an OSPF FAD TLV. If it appears more than once, the OSPF FAD TLVMUST<bcp14>MUST</bcp14> be ignored by the receiver.</t> </section> <section anchor="OSPFFLEXALGINCANYTLV"title="OSPFnumbered="true" toc="default"> <name>OSPF Flexible Algorithm Include-Any Reverse Admin GroupSub-TLV">Sub-TLV</name> <t>The OSPF Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV is used to advertise the include-any rule that is used during the Flex-Algorithm path calculation as specified in <xreftarget="FLEXALGPATHCALC"/>.</t>target="FLEXALGPATHCALC" format="default"/>.</t> <t>The format of the OSPF Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV is identical to the format of the OSPF FAERAG Sub-TLV in <xreftarget="OSPFFLEXALGEXLTLV"/>.</t>target="OSPFFLEXALGEXLTLV" format="default"/>.</t> <t>IANA has assigned Type value of 11 for the OSPF Flexible Algorithm Include-Any Reverse Admin Group Sub-TLV.</t> <t>The OSPF Flexible Algorithm Include-Any Reverse Admin Group Sub-TLVMUST NOT<bcp14>MUST NOT</bcp14> appear more than once in an OSPF FAD TLV. If it appears more than once, the OSPF FAD TLVMUST<bcp14>MUST</bcp14> be ignored by the receiver.</t> </section> <section anchor="OSPFFLEXALGINCALLTLV"title="OSPFnumbered="true" toc="default"> <name>OSPF Flexible Algorithm Include-All Reverse Admin GroupSub-TLV">Sub-TLV</name> <t>The OSPF Flexible Algorithm Include-All Reverse Admin Group Sub-TLV is used to advertise the include-all rule that is used during the Flex-Algorithm path calculation as specified in <xreftarget="FLEXALGPATHCALC"/>.</t>target="FLEXALGPATHCALC" format="default"/>.</t> <t>The format of the OSPF Flexible Algorithm Include-All Reverse Admin Group Sub-TLV is identical to the format of the OSPF FAERAG Sub-TLV in <xreftarget="OSPFFLEXALGEXLTLV"/>.</t>target="OSPFFLEXALGEXLTLV" format="default"/>.</t> <t>IANA has assigned Type value of 12 for the OSPF Flexible Algorithm Include-All Reverse Admin Group Sub-TLV.</t> <t>The OSPF Flexible Algorithm Include-All Reverse Admin Group Sub-TLVMUST NOT<bcp14>MUST NOT</bcp14> appear more than once in an OSPF FAD TLV. If it appears more than once, the OSPF FAD TLVMUST<bcp14>MUST</bcp14> be ignored by the receiver.</t> </section> <section anchor="FLEXALGPATHCALC"title="Calculationnumbered="true" toc="default"> <name>Calculation of Flexible AlgorithmPaths">Paths</name> <t>The following procedures augment the rules defined inSection 13 of<xreftarget="RFC9350"/>target="RFC9350" section="13"/> by introducing additional constraints based on Administrative Groups (AGs) associated with the reverse direction of a link.<list style="hanging"> <t>Check</t> <!--[rfced] As this text is repeated in Table 1, may we remove it from Section 11 to avoid redundancy? Original: Check if any exclude reverse Admin Group rule is part of theFlex-AlgorithmFlex- Algorithm definition. If such exclude rule exists, check if any Admin Group that is part of the exclude rule is also set on the link in the reverse direction. If such Admin Group is set on the link in the reverse direction, the link MUST be pruned from thecomputation.</t> <t>Checkcomputation. Check if any include-any reverse Admin Group rule is part of the Flex-Algorithm definition. If such include-any rule exists, check if any Admin Group that is part of the include-any rule is also set on the link in the reverse direction. If no such Admin Group is set on the link in the reverse direction, the link MUST be pruned from thecomputation.</t> <t>Checkcomputation. Check if any include-all reverse Admin Group rule is part of the Flex-Algorithm definition. If such include-all rule exists, check if all Admin Groups that are part of the include-all rule are also set on the link in the reverse direction. If all such Admin Groups are not set on the link in the reverse direction, the link MUST be pruned from thecomputation.</t> </list></t>computation. --> <ul spacing="normal" > <li>Check if any exclude reverse Admin Group rule is part of the Flex-Algorithm definition. If such exclude rule exists, check if any Admin Group that is part of the exclude rule is also set on the link in the reverse direction. If such Admin Group is set on the link in the reverse direction, the link <bcp14>MUST</bcp14> be pruned from the computation.</li> <li>Check if any include-any reverse Admin Group rule is part of the Flex-Algorithm definition. If such include-any rule exists, check if any Admin Group that is part of the include-any rule is also set on the link in the reverse direction. If no such Admin Group is set on the link in the reverse direction, the link <bcp14>MUST</bcp14> be pruned from the computation.</li> <li>Check if any include-all reverse Admin Group rule is part of the Flex-Algorithm definition. If such include-all rule exists, check if all Admin Groups that are part of the include-all rule are also set on the link in the reverse direction. If all such Admin Groups are not set on the link in the reverse direction, the link <bcp14>MUST</bcp14> be pruned from the computation.</li> </ul> <t>Please see rules 8, 9, and 10 in <xreftarget="PATHCOMPREGISTRY"/>target="PATHCOMPREGISTRY" format="default"/> for these added rules.</t> </section> <!--[rfced] May the content of Section 12 be moved under Section 13.3 or become a subsection? Rationale: Section 12 provides guidance to designated experts when evaluating new registrations in the registry described in Section 13.3. Original: 12. IGP Flex-Algorithm Path Computation Rules Registry 13. IANA Considerations 13.1. Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 13.2. OSPF Flexible Algorithm Definition TLV Sub-TLV Registry 13.3. IGP Flex-Algorithm Path Computation Rules Registry Perhaps: 12. IANA Considerations 12.1. Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV 12.2. OSPF Flexible Algorithm Definition TLV Sub-TLV Registry 12.3. IGP Flex-Algorithm Path Computation Rules Registry 12.3.1. Guidance for Designated Experts [where 12.3.1 contains the original section 12] If so, the two mentions of Section 12 would be updated accordingly: Original: Section 12 provides guidance for designated experts. Perhaps: Section 12.3.1 provides guidance for designated experts. Original: (refer to Section 12) Perhaps: (refer to Section 12.3.1) --> <section anchor="NEW_REG"title="IGPnumbered="true" toc="default"> <name>IGP Flex-Algorithm Path Computation RulesRegistry">Registry</name> <t>Since the original Flex-Algorithm specification <xreftarget="RFC9350"/>,target="RFC9350" format="default"/>, many Flex-Algorithm extensions have been proposed and standardized. Many of them added additional rules to the Flex-Algorithm path computation. Maintaining an IANA registry for these rules allows specification across multiple documents progressing independently. The new "IGP Flex-Algorithm Path Computation Rules" registry has been created and is specified in <xreftarget="PATHCOMPREGISTRY"/>.</t>target="PATHCOMPREGISTRY" format="default"/>.</t> <t>This section provides the guidance for designated experts on evaluating new registrations in the "IGP Flex-Algorithm Path Computation Rules" registry:</t> <ol spacing="normal"type="1" indent="adaptive" start="1"> <li derivedCounter="1."> <t>Whentype="1"> <li> When a new constraint is defined, the rule associated with that constraintMAY<bcp14>MAY</bcp14> be inserted at any position. Backwards compatibility is guaranteed because nodeswhichthat don't support the new constraint will not participate in an algorithm where the FAD specifies a constraint they don'tsupport.</t>support. </li><li derivedCounter="2."> <t>The<li> The relative ordering of existing rulesMUST NOT<bcp14>MUST NOT</bcp14> be altered. Doing so has the potential to create backwards compatibilityissues.</t>issues. </li><li derivedCounter="3."> <t>Deletion<li> Deletion of the rulesMUST NOT<bcp14>MUST NOT</bcp14> be done. Given that the rules are only used conditionally based on the information carried in the winning FAD, deletion of the rule is notnecessary.</t>necessary. </li><li derivedCounter="4."> <t>Merging<li> Merging or repeating of the rulesMUST NOT<bcp14>MUST NOT</bcp14> bedone.</t>done. </li> </ol> </section> <section anchor="IANA"title="IANA Considerations">numbered="true" toc="default"> <name>IANA Considerations</name> <section anchor="SUBTLVREGISTRY"title="Sub-Sub-TLVsnumbered="true" toc="default"> <name>Sub-Sub-TLVs for Flexible Algorithm DefinitionSub-TLV"> <t>This document makesSub-TLV</name> <t>IANA has registered the followingregistrationin the "IS-IS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV" registry under the "IS-IS TLV Codepoints" registry group:<list style="hanging"> <t>Type: 10</t> <t>Description: Flexible</t> <dl newline="false" spacing="compact"> <dt>Type:</dt><dd>10</dd> <dt>Description:</dt><dd>Flexible Algorithm Exclude Reverse AdminGroup</t> <t>MP-TLV Applicability: N</t> <t>Reference: This document (<xref target="ISISFLEXALGEXLTLV"/>).</t> </list> <list style="hanging"> <t>Type: 11</t> <t>Description: FlexibleGroup</dd> <dt>MP:</dt><dd>n</dd> <dt>Reference:</dt><dd>RFC 9917, <xref target="ISISFLEXALGEXLTLV" format="default"/></dd> </dl> <dl newline="false" spacing="compact"> <dt>Type:</dt><dd>11</dd> <dt>Description:</dt><dd>Flexible Algorithm Include-Any Reverse AdminGroup</t> <t>MP-TLV Applicability: N</t> <t>Reference: This document (<xref target="ISISFLEXALGINCANYTLV"/>).</t> </list> <list style="hanging"> <t>Type: 12</t> <t>Description: FlexibleGroup</dd> <dt>MP:</dt><dd>n</dd> <dt>Reference:</dt><dd>RFC 9917, <xref target="ISISFLEXALGINCANYTLV" format="default"/></dd> </dl> <dl newline="false" spacing="compact"> <dt>Type:</dt><dd>12</dd> <dt>Description:</dt><dd>Flexible Algorithm Include-All Reverse AdminGroup</t> <t>MP-TLV Applicability: N</t> <t>Reference: This document (<xref target="ISISFLEXALGINCALLTLV"/>).</t> </list></t>Group</dd> <dt>MP:</dt><dd>n</dd> <dt>Reference:</dt><dd>RFC 9917, <xref target="ISISFLEXALGINCALLTLV" format="default"/></dd> </dl> </section> <sectiontitle="OSPFnumbered="true" toc="default"> <name>OSPF Flexible Algorithm Definition TLV Sub-TLVRegistry">Registry</name> <t>This document makes the following registration in the "OSPF Flexible Algorithm Definition TLV Sub-TLVs" registry under the "Open Shortest Path First (OSPF) Parameters" registry group:<list style="hanging"> <t>Type: 10</t> <t>Description: Flexible</t> <dl newline="false" spacing="compact"> <dt>Type:</dt><dd>10</dd> <dt>Description:</dt><dd>Flexible Algorithm Exclude Reverse AdminGroup</t> <t>Reference: This document (<xref target="OSPFFLEXALGEXLTLV"/>).</t> </list> <list style="hanging"> <t>Type: 11</t> <t>Description: FlexibleGroup</dd> <dt>Reference:</dt><dd>RFC 9917, <xref target="OSPFFLEXALGEXLTLV" format="default"/></dd> </dl> <dl newline="false" spacing="compact"> <dt>Type:</dt><dd>11</dd> <dt>Description:</dt><dd>Flexible Algorithm Include-Any Reverse AdminGroup</t> <t>Reference: This document (<xref target="OSPFFLEXALGINCANYTLV"/>).</t> </list> <list style="hanging"> <t>Type: 12</t> <t>Description: FlexibleGroup</dd> <dt>Reference:</dt><dd>RFC 9917, <xref target="OSPFFLEXALGINCANYTLV" format="default"/></dd> </dl> <dl newline="false" spacing="compact"> <dt>Type:</dt><dd>12</dd> <dt>Description:</dt><dd>Flexible Algorithm Include-All Reverse AdminGroup</t> <t>Reference: This document (<xref target="OSPFFLEXALGINCALLTLV"/>).</t> </list></t>Group</dd> <dt>Reference:</dt><dd>RFC 9917, <xref target="OSPFFLEXALGINCALLTLV" format="default"/></dd> </dl> </section> <section anchor="PATHCOMPREGISTRY"title="IGPnumbered="true" toc="default"> <name>IGP Flex-Algorithm Path Computation RulesRegistry"> <t>This document createsRegistry</name> <t>IANA has created a new registry called "IGP Flex-Algorithm Path ComputationRules Registry"Rules" within the "Interior Gateway Protocol (IGP) Parameters" registry group. The registration procedure for the new registry is"Expert Review".Expert Review <xref target="RFC8126"/>. <xreftarget="NEW_REG"/>target="NEW_REG" format="default"/> provides guidance forDesignated Experts.</t>designated experts.</t> <t>The "IGPFlex-AlgoFlex-Algorithm Path Computation Rules" registry specifies the ordered set of rules that are used to prune links from the topology during the Flex-Algorithm path computation.</t> <t>There is no upper bound on the number of rules that the registry supports.</t> <!--[rfced] For the sake of the reader, would you like to add a sentence to explain "FAEMB" and "FAEMB", which are used in the descriptions within Table 1? It could appear directly before table, perhaps: In Table 1, "FAEMB" means "Flex-Algorithm Exclude Minimum Bandwidth", and "FAEMD" means "Flex-Algorithm Exclude Maximum Delay". --> <tablealign="center" pn="table-6"> <name slugifiedName="name-is-is-sub-sub-tlvs-for-flexi">IGP Flex-algoalign="center"> <name>IGP Flex-Algorithm Path Calculation Rules</name> <thead> <tr><th align="left" colspan="1" rowspan="1">Sequence<th>Sequence Number</th><th align="left" colspan="1" rowspan="1">Description</th> <th align="left" colspan="1" rowspan="1">Reference</th><th>Description</th> <th>Reference</th> </tr> </thead> <tbody> <tr><td align="left" colspan="1" rowspan="1">1</td> <td align="left" colspan="1" rowspan="1">Check<td>1</td> <td>Check if any exclude Administrative Group rule is part of the Flex-Algorithm Definition. If such exclude rule exists, check if any color that is part of the exclude rule is also set on the link. If such a color is set, the linkMUST<bcp14>MUST</bcp14> be pruned from the computation</td><td align="left" colspan="1" rowspan="1">Section 13 of <xref target="RFC9350"/></td><td><xref target="RFC9350" section="13"/></td> </tr> <tr><td align="left" colspan="1" rowspan="1">2</td> <td align="left" colspan="1" rowspan="1">Check<td>2</td> <td>Check if any exclude SRLG rule is part of the Flex-Algorithm Definition. If such exclude rule exists, check if the link is part of any SRLG that is also part of the SRLG exclude rule. If the link is part of such SRLG, the linkMUST<bcp14>MUST</bcp14> be pruned from the computation.</td><td align="left" colspan="1" rowspan="1">Section 13 of <xref target="RFC9350"/></td><td><xref target="RFC9350" section="13"/></td> </tr> <tr><td align="left" colspan="1" rowspan="1">3</td> <td align="left" colspan="1" rowspan="1">Check<td>3</td> <td>Check if any include-any Administrative Group rule is part of the Flex-Algorithm Definition. If such include-any rule exists, check if any color that is part of the include-any rule is also set on the link. If no such color is set, the linkMUST<bcp14>MUST</bcp14> be pruned from thecomputation</td> <td align="left" colspan="1" rowspan="1">Section 13 of <xref target="RFC9350"/></td>computation.</td> <td><xref target="RFC9350" section="13"/></td> </tr> <tr><td align="left" colspan="1" rowspan="1">4</td> <td align="left" colspan="1" rowspan="1">Check<td>4</td> <td>Check if any include-all Administrative Group rule is part of the Flex-Algorithm Definition. If such include-all rule exists, check if all colors that are part of the include-all rule are also set on the link. If all such colors are not set on the link, the linkMUST<bcp14>MUST</bcp14> be pruned from the computation.</td><td align="left" colspan="1" rowspan="1">Section 13 of <xref target="RFC9350"/></td><td><xref target="RFC9350" section="13"/></td> </tr> <tr><td align="left" colspan="1" rowspan="1">5</td> <td align="left" colspan="1" rowspan="1">If<td>5</td> <td>If the Flex-Algorithm Definition uses something other than the IGP metric(Section 5 of <xref target="RFC9350"/>),(<xref target="RFC9350" section="5"/>), and such metric is not advertised for the particular link in a topology for which the computation is done, such linkMUST<bcp14>MUST</bcp14> be pruned from the computation. A metric of value 0MUST NOT<bcp14>MUST NOT</bcp14> be assumed in such a case.</td><td align="left" colspan="1" rowspan="1">Section 13 of <xref target="RFC9350"/></td><td><xref target="RFC9350" section="13"/></td> </tr> <tr><td align="left" colspan="1" rowspan="1">6</td> <td align="left" colspan="1" rowspan="1"><td>6</td> <td> Check if any exclude FAEMB rule is part of the Flex-Algorithm definition. If such exclude rule exists and the link has Maximum Link Bandwidth advertised, check if the link bandwidth satisfies the FAEMB rule. If the link does not satisfy the FAEMB rule, the linkMUST<bcp14>MUST</bcp14> be pruned from the Flex-Algorithm computation</td><td align="left" colspan="1" rowspan="1">Section 6 of <xref target="I-D.ietf-lsr-flex-algo-bw-con"/></td><td><xref section="6" target="RFC9843"/></td> </tr> <tr><td align="left" colspan="1" rowspan="1">7</td> <td align="left" colspan="1" rowspan="1">Check<td>7</td> <td>Check if any exclude FAEMD rule is part of the Flex-Algorithm definition. If such exclude rule exists and the link has Min Unidirectional link delay advertised, check if the link delay satisfies the FAEMD rule. If the link does not satisfy the FAEMD rule, the linkMUST<bcp14>MUST</bcp14> be pruned from the Flex-Algorithm computation.</td><td align="left" colspan="1" rowspan="1">Section 6 of <xref target="I-D.ietf-lsr-flex-algo-bw-con"/></td><td><xref section="6" target="RFC9843"/></td> </tr> <tr><td align="left" colspan="1" rowspan="1">8</td> <td align="left" colspan="1" rowspan="1">Check<td>8</td> <td>Check if any exclude reverse Admin Group rule is part of the Flex-Algorithm definition. If such exclude rule exists, check if any Admin Group that is part of the exclude rule is also set on the link in the reverse direction. If such Admin Group is set on the link in the reverse direction, the linkMUST<bcp14>MUST</bcp14> be pruned from the computation.</td><td align="left" colspan="1" rowspan="1">This document, <xref target="FLEXALGPATHCALC"/></td><td><xref target="FLEXALGPATHCALC"/> of RFC 9917</td> </tr> <tr><td align="left" colspan="1" rowspan="1">9</td> <td align="left" colspan="1" rowspan="1">Check<td>9</td> <td>Check if any include-any reverse Admin Group rule is part of the Flex-Algorithm definition. If such include-any rule exists, check if any Admin Group that is part of the include-any rule is also set on the link in the reverse direction. If no such Admin Group is set on the link in the reverse direction, the linkMUST<bcp14>MUST</bcp14> be pruned from the computation</td><td align="left" colspan="1" rowspan="1">This document, <xref target="FLEXALGPATHCALC"/></td><td><xref target="FLEXALGPATHCALC"/> of RFC 9917</td> </tr> <tr><td align="left" colspan="1" rowspan="1">10</td> <td align="left" colspan="1" rowspan="1">Check<td>10</td> <td>Check if any include-all reverse Admin Group rule is part of the Flex-Algorithm definition. If such include-all rule exists, check if all Admin Groups that are part of the include-all rule are also set on the link in the reverse direction. If all such Admin Groups are not set on the link in the reverse direction, the linkMUST<bcp14>MUST</bcp14> be pruned from the computation.</td><td align="left" colspan="1" rowspan="1">This document, <xref target="FLEXALGPATHCALC"/></td><td><xref target="FLEXALGPATHCALC"/> of RFC 9917</td> </tr> </tbody> </table> </section> </section> <section anchor="Security"title="Security Considerations">numbered="true" toc="default"> <name>Security Considerations</name> <t>This document inherits security considerations from <xreftarget="RFC9350"/>.</t> </section> <section anchor="Acknowledgements" title="Acknowledgements"> <t>TBD</t>target="RFC9350" format="default"/>.</t> </section> </middle> <back><references title="Normative References"> <?rfc include='reference.RFC.2119'?> <?rfc include='reference.RFC.8174'?> <?rfc include='reference.RFC.7308'?> <?rfc include='reference.RFC.9350'?> <?rfc include='reference.I-D.ietf-lsr-flex-algo-bw-con'?><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.7308.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9350.xml"/> <!-- [RFC9843] draft-ietf-lsr-flex-algo-bw-con-22 companion doc RFC YYY1 Published 09/12/25 --> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9843.xml"/> </references> <references> <name>Informative References</name> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8126.xml"/> </references> <!--[rfced] The Acknowledgments section is currently populated with "TBD". Please let us know if/what text should be added here. --> <section anchor="Acknowledgments" numbered="false" toc="default"> <name>Acknowledgments</name> <t>TBD</t> </section> <!-- [rfced] FYI - We have added expansions for the following abbreviations per Section 3.6 of RFC 7322 ("RFC Style Guide"). Please review each expansion in the document carefully to ensure correctness. Cyclic Redundancy Check (CRC) Link State Advertisement (LSA) Label Switched Path (LSP) Shortest Path First (SPF) --> <!-- [rfced] Please review the "Inclusive Language" portion of the online Style Guide <https://www.rfc-editor.org/styleguide/part2/#inclusive_language> and let us know if any changes are needed. Updates of this nature typically result in more precise language, which is helpful for readers. Note that our script did not flag any words in particular, but this should still be reviewed as a best practice. --> </back> </rfc>