<?xml version="1.0"encoding="US-ASCII"?>encoding="UTF-8"?> <!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" submissionType="IETF" category="std" consensus="true" docName="draft-ietf-lsr-isis-rfc5316bis-07" number="9346" ipr="trust200902"obsoletes="5316">obsoletes="5316" updates="" xml:lang="en" tocInclude="true" tocDepth="3" symRefs="true" sortRefs="true" version="3"> <!-- xml2rfc v2v3 conversion 3.15.0 --> <front> <titleabbrev="ISISabbrev="IS-IS Extensions for Inter-AS TE">IS-IS Extensions in Support of Inter-Autonomous System (AS) MPLS and GMPLS Traffic Engineering</title> <seriesInfo name="RFC" value="9346"/> <author fullname="Mach(Guoyi) Chen" initials="M." surname="Chen"> <organization>Huawei</organization> <address> <email>mach.chen@huawei.com</email> </address> </author> <author fullname="Les Ginsberg" initials="L." surname="Ginsberg"> <organization>Cisco Systems</organization> <address> <email>ginsberg@cisco.com</email> </address> </author> <author fullname="Stefano Previdi" initials="S." surname="Previdi"> <organization>Huawei Technologies</organization> <address> <postal> <street/> <city/> <code/><country>IT</country><country>Italy</country> </postal> <email>stefano@previdi.net</email> </address> </author> <author fullname="Xiaodong Duan"initials="D." surname="Xiaodong">initials="X." surname="Duan"> <organization>China Mobile</organization> <address> <email>duanxiaodong@chinamobile.com</email> </address> </author> <dateyear="2022"/> <area>LSR Working Group</area> <workgroup>Internet Engineering Task Force</workgroup> <!-- WG name at the upperleft corner of the doc, IETF is fine for individual submissions. If this element is not present, the default is "Network Working Group", which is used by the RFC Editor as a nod to the history of the IETF. -->year="2023" month="January"/> <area>rtg</area> <workgroup>lsr</workgroup> <keyword>ISIS</keyword> <keyword>Inter-AS</keyword> <keyword>TE</keyword> <abstract> <t>This document describes extensions to the Intermediate System to Intermediate System (IS-IS) protocol to support Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS) Traffic Engineering (TE) for multiple Autonomous Systems(ASs).(ASes). It defines IS-IS extensions for the flooding of TE information about inter-AS links, which can be used to perform inter-AS TE path computation.</t> <t>No support for flooding information from within one AS to another AS is proposed or defined in this document.</t> <t> This document builds on RFC 5316 by adding support for IPv6-only operation.</t> <t>This document obsoletes RFC 5316.</t> </abstract><note title="Requirements Language"> <t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/> when, and only when, they appear in all capitals, as shown here.</t> </note></front> <middle> <section anchor="INTRO"title="Introduction">numbered="true" toc="default"> <name>Introduction</name> <t><xreftarget="RFC5305"/>target="RFC5305" format="default"/> defines extensions to the IS-IS protocol <xreftarget="RFC1195"/>target="RFC1195" format="default"/> to support intra-area Traffic Engineering (TE). The extensions provide a way of encoding the TE information for TE-enabled links within the network (TE links) and flooding this information within an area. The extended IS reachability TLV andtraffic engineeringTraffic Engineering router ID TLV, which are defined in <xreftarget="RFC5305"/>,target="RFC5305" format="default"/>, are used to carry such TE information. The extended IS reachability TLV has several nested sub-TLVs that describe the TE attributes for a TE link.</t> <t><xreftarget="RFC6119"/>target="RFC6119" format="default"/> and <xreftarget="RFC5307"/>target="RFC5307" format="default"/> define similar extensions to IS-IS in support of IPv6 andGeneralized Multiprotocol Label Switching (GMPLS) TEGMPLS TE, respectively.</t> <t>Requirements for establishing Multiprotocol Label Switching (MPLS) TE Label Switched Paths (LSPs) that cross multiple Autonomous Systems (ASes) are described in <xreftarget="RFC4216"/>.target="RFC4216" format="default"/>. As described in <xreftarget="RFC4216"/>,target="RFC4216" format="default"/>, a methodSHOULD<bcp14>SHOULD</bcp14> provide the ability to compute a path spanning multiple ASes. So a path computation entity that may be the head-end Label Switching Router (LSR), an AS Border Router (ASBR), or a Path Computation Element (PCE) <xreftarget="RFC4655"/>target="RFC4655" format="default"/> needs to know the TE information not only of the links within anAS,AS but also of the links that connect to other ASes.</t> <t>In this document,a new TLV, which is referred to astheinter-AS reachability TLV,Inter-AS Reachability Information TLV is defined to advertise inter-AS TE information, andthree newfour sub-TLVs are defined for inclusion in theinter-AS reachabilityInter-AS Reachability Information TLV to carry the information about theremoteRemote ASnumberNumber, Remote ASBR Identifier, andremoteIPv6 Local ASBRID.Identifier. The sub-TLVs defined in <xreftarget="RFC5305"/><xref target="RFC6119"/>target="RFC5305" format="default"/>, <xref target="RFC6119" format="default"/>, and other documents for inclusion in the extended IS reachability TLV for describing the TE properties of a TE link are applicable to be included in the Inter-AS Reachability Information TLV for describing the TE properties of an inter-AS TE link as well. Also, two morenew sub- TLVssub-TLVs are defined for inclusion in the IS-ISrouter capabilityRouter CAPABILITY TLV to carry the TE Router ID when the TE Router ID is needed to reach all routers within an entire IS-IS routing domain. The extensions are equally applicable to IPv4 and IPv6 as identical extensions to <xreftarget="RFC5305"/>target="RFC5305" format="default"/> and <xreftarget="RFC6119"/>.target="RFC6119" format="default"/>. Detailed definitions and procedures are discussed in the following sections.</t> <t>This document does not propose or define any mechanisms to advertise any other extra-AS TE information within IS-IS. SeeSection 2.1<xref target="non-objectives" format="default"/> for a full list of non-objectives for this work.</t> <section> <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 <xref target="RFC2119"/> <xref target="RFC8174"/> when, and only when, they appear in all capitals, as shown here.</t> </section> </section> <section anchor="_PROB"title="Problem Statement">numbered="true" toc="default"> <name>Problem Statement</name> <t>As described in <xreftarget="RFC4216"/>,target="RFC4216" format="default"/>, in the case of establishing an inter-AS TE LSP that traverses multiple ASes, the Path message <xreftarget="RFC3209"/>target="RFC3209" format="default"/> may include the following elements in the Explicit Route Object (ERO) in order to describe the path of the LSP:</t><t><list style="symbols"> <t>a<ul spacing="normal"> <li>a set of AS numbers as loosehops; and/or</t> <t>ahops and/or</li> <li>a set of LSRs including ASBRs as loosehops.</t> </list></t>hops.</li> </ul> <t>Two methods for determining inter-AS paths have been described elsewhere. The per-domain method <xreftarget="RFC5152"/>target="RFC5152" format="default"/> determines the path one domain at a time. Thebackward recursivebackward-recursive method <xreftarget="RFC5441"/>target="RFC5441" format="default"/> uses cooperation between PCEs to determine an optimum inter-domain path. The sections that follow examine how inter-AS TE link information could be useful in both cases.</t> <sectiontitle="Anumbered="true" toc="default" anchor="non-objectives"> <name>A Note onNon-Objectives">Non-objectives</name> <t>It is important to note that this document does not make any change to the confidentiality and scaling assumptions surrounding the use of ASes in the Internet. In particular, this document is conformant to the requirements set out in <xreftarget="RFC4216"/>.</t>target="RFC4216" format="default"/>.</t> <t>The following features are explicitly excluded:</t><t><list style="symbols"> <t>There<ul spacing="normal"> <li>There is no attempt to distribute TE information from within one AS to anotherAS.</t> <t>ThereAS.</li> <li>There is no mechanism proposed to distribute any form of TE reachability information for destinations outside theAS.</t> <t>ThereAS.</li> <li>There is no proposed change to the PCE architecture orusage.</t> <t>TEusage.</li> <li>TE aggregation is not supported orrecommended.</t> <t>Thererecommended.</li> <li>There is no exchange of private information betweenASes.</t> <t>NoASes.</li> <li>No IS-IS adjacencies are formed on the inter-ASlink.</t> </list></t>link.</li> </ul> </section> <sectiontitle="Per-Domainnumbered="true" toc="default" anchor="determiniation"> <name>Per-Domain PathDetermination">Determination</name> <t>In the per-domain method of determining an inter-AS path for an MPLS-TE LSP, when an LSR that is an entry-point to an AS receives a Path message from an upstream AS with an ERO containing a next hop that is an AS number, it needs to find which LSRs (ASBRs) within the local AS are connected to the downstream AS. That way, it can compute a TE LSP segment across the local AS to one of those LSRs and forward the Path message to that LSR and hence into the next AS. See Figure 1 for an example.</t><t><figure> <artwork><![CDATA[<figure> <name>Inter-AS Reference Model</name> <artwork name="" type="" align="left" alt=""><![CDATA[ R1------R3----R5-----R7------R9-----R11 | | \ | / | | | \ | ---- | | | \ | / | R2------R4----R6 --R8------R10----R12 : : <-- AS1 -->:<---- AS2 --->:<--- AS3 --->Figure 1: Inter-AS Reference Model]]></artwork></figure>The</figure> <t>The figure shows three ASes (AS1, AS2, and AS3) and twelve LSRs (R1 through R12). R3 and R4 are ASBRs in AS1. R5, R6, R7, and R8 are ASBRs in AS2. R9 and R10 are ASBRs in AS3.</t> <t>If an inter-AS TE LSP is planned to be established from R1 to R12, the AS sequence will be: AS1, AS2, AS3.</t> <t>Suppose that the Path message enters AS2 from R3. The next hop in the ERO shows AS3, and R5 must determine a path segment across AS2 to reach AS3. It has a choice of three exit points from AS2 (R6, R7, and R8), and it needs to know which of these provide TE connectivity toAS3,AS3 and whether the TE connectivity (for example, available bandwidth) is adequate for the requested LSP.</t> <t>Alternatively, if the next hop in the ERO is an entry ASBR for AS3 (say R9), R5 needs to know which of its exit ASBRs has a TE link that connects to R9. Since there may be multiple ASBRs that are connected to R9 (both R7 and R8 in this example), R5 also needs to know the TE properties of the inter-AS TE links so that it can select the correct exit ASBR.</t> <t>Once the Path message reaches the exit ASBR, any choice of inter-AS TE link can be made by the ASBR if not already made by the entry ASBR that computed the segment.</t> <t>More details can be found inSection 4 of<xreftarget="RFC5152"/>,target="RFC5152" section="4" sectionFormat="of" format="default"/>, which clearly points out why advertising of inter-AS links is desired.</t> <t>To enable R5 to make the correct choice of exit ASBR, the following information is needed:</t><t><list style="symbols"> <t>List<ul spacing="normal"> <li>List of all inter-AS TE links for the localAS.</t> <t>TEAS.</li> <li>TE properties of each inter-AS TElink.</t> <t>ASlink.</li> <li>AS number of the neighboring AS connected to by each inter-AS TElink.</t> <t>Identitylink.</li> <li>Identity (TE Router ID) of the neighboring ASBR connected to by each inter-AS TElink.</t> </list>Inlink.</li> </ul> <t>In GMPLS networks, further information may also be required to select the correct TE links as defined in <xreftarget="RFC5307"/>.</t>target="RFC5307" format="default"/>.</t> <t>The example above shows how this information is needed at the entry-point ASBRs for each AS (or the PCEs that provide computation services for the ASBRs). However, this information is also needed throughout the local AS if path computation functionality is fully distributed among LSRs in the local AS, forexampleexample, to support LSPs that have start points (ingress nodes) within the AS.</t> </section> <sectiontitle="Backward Recursivenumbered="true" toc="default"> <name>Backward-Recursive PathComputation">Computation</name> <t>Another scenario using PCE techniques has the same problem. <xreftarget="RFC5441"/>target="RFC5441" format="default"/> defines a PCE-based TE LSP computation method (calledBackward Recursive"Backward-Recursive PathComputation)Computation (BRPC)") to compute optimal inter-domain constrained MPLS-TE or GMPLS LSPs. In this path computation method, a specific set of traversed domains (ASes) are assumed to be selected before computation starts. Each downstream PCE in domain(i) returns to its upstream neighbor PCE in domain(i-1) a multipoint-to-point tree of potential paths. Each tree consists of the set of paths from all boundary nodes located in domain(i) to the destination where each path satisfies the set of required constraints for the TE LSP (bandwidth, affinities, etc.).</t> <t>So a PCE needs to select boundary nodes (that is, ASBRs) that provide connectivity from the upstream AS. In order for the tree of paths provided by one PCE to its neighbor to be correlated, the identities of the ASBRs for each path need to be referenced. Thus, the PCE must know the identities of the ASBRs in the remote AS that are reached by any inter-AS TE link, and, in order to provide only suitable paths in the tree, the PCE must know the TE properties of the inter-AS TE links. See the following figure as anexample.<figure> <artwork><![CDATA[example.</t> <figure> <name>BRPC for Inter-AS Reference Model</name> <artwork name="" type="" align="left" alt=""><![CDATA[ PCE1<------>PCE2<-------->PCE3 / : : / : : R1------R3----R5-----R7------R9-----R11 | | \ | / | | | \ | ---- | | | \ | / | R2------R4----R6 --R8------R10----R12 : : <-- AS1 -->:<---- AS2 --->:<--- AS3 --->Figure 2: BRPC for Inter-AS Reference Model]]></artwork></figure></t></figure> <t>The figure shows three ASes (AS1, AS2, and AS3), three PCEs (PCE1, PCE2, and PCE3), and twelve LSRs (R1 through R12). R3 and R4 are ASBRs in AS1. R5, R6, R7, and R8 are ASBRs in AS2. R9 and R10 are ASBRs in AS3. PCE1, PCE2, and PCE3 cooperate to perform inter-AS path computation and are responsible for path segment computation within their own domain(s).</t><t>If<t> If an inter-AS TE LSP is planned to be established from R1 to R12, the traversed domains are assumed to beselected: AS1->AS2->AS3,selected (AS1->AS2->AS3), and the PCE chainis:is PCE1->PCE2->PCE3. First, the path computation request originated from thePCCPath Computation Client (PCC) (R1) is relayed by PCE1 and PCE2 along the PCE chain to PCE3. Then, PCE3 begins to compute the path segments from the entry boundary nodes that provide connection from AS2 to the destination (R12). But, to provide suitable path segments, PCE3 must determine which entry boundary nodes provide connectivity to its upstream neighbor AS (identified by its ASnumber),number) and must know the TE properties of the inter-AS TE links. In the same way, PCE2 also needs to determine the entry boundary nodes according to its upstream neighbor AS and the inter-AS TE link capabilities.</t> <t>Thus, to supportBackward Recursive Path Computation,BRPC, the same information listed inSection 2.2<xref target="determiniation" format="default"/> is required. The AS number of the neighboring AS connected to by each inter-AS TE link is particularly important.</t> </section> </section> <section anchor="_SOL"title="Extensionsnumbered="true" toc="default"> <name>Extensions toISIS-TE">IS-IS TE</name> <t>Note that this document does not define mechanisms for distribution of TE information from one AS to another, does not distribute any form of TE reachability information for destinations outside the AS, does not change the PCE architecture or usage, does not suggest or recommend any form of TE aggregation, and does not feed private information between ASes. SeeSection 2.1.</t><xref target="non-objectives" format="default"/>.</t> <t>In this document, the Inter-AS Reachability Information TLV is defined for the advertisement of inter-AS TElinks, a new TLV, which is referred to as the inter-AS reachability TLV, is defined. Three newlinks. Four sub-TLVs are also defined for inclusion in theinter-AS reachabilityInter-AS Reachability Information TLV to carry the information about the neighboring ASnumber andnumber, theremoteRemote ASBRIDIdentifier, and IPv6 Local ASBR Identifier of an inter-AS link. The sub-TLVs defined in <xreftarget="RFC5305"/>,target="RFC5305" format="default"/>, <xreftarget="RFC6119"/>,target="RFC6119" format="default"/>, and other documents for inclusion in the extended IS reachability TLV are applicable to be included in theinter-AS reachabilityInter-AS Reachability Information TLV for the advertisement of inter-AS TElinks advertisement.</t>links.</t> <t>This document also defines twonewsub-TLVs for inclusion in the IS-ISrouter capabilityRouter CAPABILITY TLV to carry the TE Router ID when the TE Router ID is needed to reach all routers within an entire IS-IS routing domain.</t> <t>While some of the TE information of an inter-AS TE link may be available within the AS from other protocols, in order to avoid any dependency on where such protocols are processed, this mechanism carries all the information needed for the required TE operations.</t> <section anchor="_RID"title="Choosingnumbered="true" toc="default"> <name>Choosing the TE Router IDValue">Value</name> <t>Subsequent sections specify advertisement of a TE Router ID value for IPv4 and/or IPv6. This section defines how this value is chosen. </t> <t>A TE Router IDMUST<bcp14>MUST</bcp14> be an addresswhichthat is unique within the IS-IS domain andstablestable, i.e., it can always be referenced in a path that will be reachable from multiple hops away, regardless of the state of the node's interfaces.</t> <t>When advertising an IPv4 address as a TE Router ID, if the Traffic EngineeringRouterrouter ID TLV <xreftarget="RFC5305"/>target="RFC5305" format="default"/> is being advertised, then the addressSHOULD<bcp14>SHOULD</bcp14> be identical to the address in the Traffic EngineeringRouterrouter ID TLV. The TE Router IDMAY<bcp14>MAY</bcp14> be identical to an IP Interface Address <xreftarget="RFC1195"/>target="RFC1195" format="default"/> advertised by the originating IS so long as the address meets the requirements specified above.</t> <t>When advertising an IPv6 address as a TE Router ID, if the IPv6 TE Router ID TLV <xreftarget="RFC6119"/>target="RFC6119" format="default"/> is being advertised, then the addressSHOULD<bcp14>SHOULD</bcp14> be identical to the address in the IPv6 TE Router ID TLV. The TE Router IDMAY<bcp14>MAY</bcp14> be identical to a non-link-local IPv6 Interface Address advertised by the originating IS in a Link State PDU using the IPv6Intf. AddrInterface Address TLV <xreftarget="RFC5308"/>target="RFC5308" format="default"/> so long as the address meets the requirements specified above.</t> </section> <sectiontitle="Inter-ASnumbered="true" toc="default" anchor="inter-as"> <name>Inter-AS ReachabilityTLV">Information TLV</name> <t>Theinter-AS reachabilityInter-AS Reachability Information TLV has type 141 (seeSection 6.1)<xref target="inter-as-reachability" format="default"/>) and contains a data structure consisting of:</t><t><figure> <artwork><![CDATA[<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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Router ID (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |default metricDefault Metric | (3 octets) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | (1 octet) +-+-+-+-+-+-+-+-+|sub-TLVs length||Sub-TLVs Length| (1 octet) +-+-+-+-+-+-+-+-+-+-+-+- |sub-TLVsSub-TLVs ... (0-246 octets) +-+-+-+-+-+-+-+-+-+-+-+-Flags]]></artwork> <t>Flags consists of thefollowing:following:</t> <artwork name="" type="" align="left" alt=""><![CDATA[ 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |S|D| Rsvd | +-+-+-+-+-+-+-+-+where: S bit: If]]></artwork> <t>where:</t> <dl newline="false" spacing="normal"> <dt>S bit:</dt> <dd>If the S bit is set(1), the Inter-AS Reachability Information TLVMUST<bcp14>MUST</bcp14> be flooded across the entire routing domain. If the S bit is not set(0), the TLVMUST NOT<bcp14>MUST NOT</bcp14> be leaked between levels. This bitMUST NOT<bcp14>MUST NOT</bcp14> be altered during the TLVleaking. D bit: Whenleaking.</dd> <dt>D bit:</dt> <dd>When the Inter-AS Reachability Information TLV is leaked from Level 2 (L2) to Level 1 (L1), the D bitMUST<bcp14>MUST</bcp14> be set. Otherwise, this bitMUST<bcp14>MUST</bcp14> be clear. Inter-AS Reachability Information TLVs with the D bit setMUST NOT<bcp14>MUST NOT</bcp14> be leaked from Level 1 to Level 2. This is to prevent TLVlooping. Reserved(Rsvd)looping.</dd> <dt>Reserved (Rsvd):</dt> <dd>Reserved bitsMUST<bcp14>MUST</bcp14> be zero when originated and ignored whenreceived. ]]></artwork> </figure>Comparedreceived.</dd> </dl> <t>Compared to the extended IS reachabilityTLVTLV, which is defined in <xreftarget="RFC5305"/>,target="RFC5305" format="default"/>, theinter-AS reachabilityInter-AS Reachability Information TLV replaces the "7 octets of System ID and Pseudonode Number" field with a "4 octets of Router ID" field and introduces an extra "control information" field, which consists of a flooding-scope bit (S bit), an up/down bit (D bit), and 6 reserved bits.</t> <t>The Router ID field of theinter-AS reachabilityInter-AS Reachability Information TLV is 4 octets in length and has a value as defined in <xreftarget="_RID"/>.target="_RID" format="default"/>. If the originating node does not support IPv4, then the reserved value 0.0.0.0MUST<bcp14>MUST</bcp14> be used in the Router IDfieldfield, and the IPv6 Router ID sub-TLVMUST<bcp14>MUST</bcp14> be present in theinter-AS reachabilityInter-AS Reachability Information TLV. The Router ID could be used to indicate the source of theinter-AS reachabilityInter-AS Reachability Information TLV.</t> <t>The flooding procedures forinter-AS reachabilitythe Inter-AS Reachability Information TLV are identical to the flooding procedures for the GENINFO TLV, which are defined inSection 4 of<xreftarget="RFC6823"/>.target="RFC6823" section="4" sectionFormat="of" format="default"/>. These procedures have been previously discussed in <xreftarget="RFC7981"/>.target="RFC7981" format="default"/>. The flooding-scope bit (S bit)SHOULD<bcp14>SHOULD</bcp14> be set to 0 if the flooding scope is to be limited to within the single IGP area to which the ASBR belongs. ItMAY<bcp14>MAY</bcp14> be set to 1 if the information is intended to reach all routers (including area border routers, ASBRs, and PCEs) in the entire IS-IS routing domain. The choice between the use of 0 or 1 is an AS-wide policy choice, and configuration controlSHOULD<bcp14>SHOULD</bcp14> be provided in ASBR implementations that support the advertisement of inter-AS TE links.</t> <t>The sub-TLVs defined in <xreftarget="RFC5305"/>,target="RFC5305" format="default"/>, <xreftarget="RFC6119"/>,target="RFC6119" format="default"/>, and other documents for describing the TE properties of a TE link are also applicable to theinter-AS reachabilityInter-AS Reachability Information TLV for describing the TE properties of anInter-ASinter-AS TE link. Apart from these sub-TLVs, fournewsub-TLVs are defined for inclusion in theinter-AS reachabilityInter-AS Reachability Information TLV defined in this document:</t><t><figure> <artwork><![CDATA[Sub-TLV type Length Name ------------ ------ --------------------------- 24 4 remote AS number 25 4 IPv4 remote<table align="center"> <thead> <tr> <th>Sub-TLV type</th> <th>Length</th> <th>Name</th> </tr> </thead> <tbody> <tr> <td>24</td> <td>4</td> <td>Remote AS Number</td> </tr> <tr> <td>25</td> <td>4</td> <td>IPv4 Remote ASBRidentifier 26 16 IPv6 remoteIdentifier</td> </tr> <tr> <td>26</td> <td>16</td> <td>IPv6 Remote ASBRidentifier TBD1 16 IPv6 localIdentifier</td> </tr> <tr> <td>45</td> <td>16</td> <td>IPv6 Local ASBRidentifier ]]></artwork> </figure>DetailedIdentifier</td> </tr> </tbody> </table> <t>Detailed definitions ofthethese fournewsub-TLVs are described in Sections3.3.1, 3.3.2, 3.3.3,<xref target="remote-as" format="counter"/>, <xref target="ipv4-remote" format="counter"/>, <xref target="ipv6-remote" format="counter"/>, and3.3.4.</t><xref target="ipv6-local" format="counter"/>.</t> </section> <sectiontitle="TEnumbered="true" toc="default"> <name>TE RouterID">ID</name> <t>The Traffic Engineering router ID TLV and IPv6 TE Router ID TLV, which are defined in <xreftarget="RFC5305"/>target="RFC5305" format="default"/> and <xreftarget="RFC6119"/>target="RFC6119" format="default"/>, respectively, only have areaflooding-scope.flooding scope. When performing inter-AS TE, the TE Router IDMAY<bcp14>MAY</bcp14> be needed to reach all routers within an entire IS-IS routingdomaindomain, and itMUST<bcp14>MUST</bcp14> have the same flooding scope as the Inter-AS Reachability Information TLV does.</t> <t><xreftarget="RFC7981"/>target="RFC7981" format="default"/> defines a generic advertisement mechanism forIS-ISIS-IS, which allows a router to advertise its capabilities within an IS-IS area or an entire IS-IS routing domain. <xreftarget="RFC7981"/>target="RFC7981" format="default"/> also points out that the TE Router ID is a candidate to be carried in the IS-ISrouter capabilityRouter CAPABILITY TLV when performing inter-area TE.</t> <t>This document uses such mechanism for TE Router ID advertisement when the TE Router ID is needed to reach all routers within an entire IS-ISRoutingrouting domain. Twonewsub-TLVs are defined for inclusion in the IS-IS RouterCapabilityCAPABILITY TLV to carry the TE Router IDs.</t><t><figure> <artwork><![CDATA[Sub-TLV type Length Name ------------ ------ ----------------- 11 4 IPv4 TE Router ID 12 16 IPv6 TE Router ID ]]></artwork> </figure>Detailed<table align="center"> <thead> <tr> <th>Sub-TLV type</th> <th>Length</th> <th>Name</th> </tr> </thead> <tbody> <tr> <td>11</td> <td>4</td> <td>IPv4 TE Router ID</td> </tr> <tr> <td>12</td> <td>16</td> <td>IPv6 TE Router ID</td> </tr> </tbody> </table> <t>Detailed definitions ofthe newthese sub-TLVs are described inSection 3.4.1Sections <xref target="remote-as" format="counter"/> and3.4.2.</t><xref target="ipv4-remote" format="counter"/>.</t> </section> <sectiontitle="Sub-TLVsnumbered="true" toc="default"> <name>Sub-TLVs for Inter-AS ReachabilityTLV">Information TLV</name> <sectiontitle="Remotenumbered="true" toc="default" anchor="remote-as"> <name>Remote AS NumberSub-TLV "> <t>A new sub-TLV, the remoteSub-TLV</name> <t>The Remote ASnumber sub-TLV,Number sub-TLV is defined for inclusion in theinter-AS reachabilityInter-AS Reachability Information TLV when advertising inter-AS links. TheremoteRemote ASnumberNumber sub-TLV specifies the AS number of the neighboring AS to which the advertised link connects.</t> <t>TheremoteRemote ASnumberNumber sub-TLV is TLV type 24 (seeSection 6.2)<xref target="sub-tlv-inter-as" format="default"/>) and is 4 octets in length. The format is as follows:</t><t><figure> <artwork><![CDATA[<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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Remote AS Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]></artwork></figure>The remote<t>The Remote ASnumberNumber field has 4 octets. When only 2 octets are used for the AS number, the left (high-order) 2 octetsMUST<bcp14>MUST</bcp14> be set to 0. TheremoteRemote ASnumberNumber sub-TLVMUST<bcp14>MUST</bcp14> be included when a router advertises an inter-AS TE link.</t> </section> <sectiontitle="IPv4numbered="true" toc="default" anchor="ipv4-remote"> <name>IPv4 Remote ASBRID Sub-TLV"> <t>A new sub-TLV, which is referred to as theIdentifier Sub-TLV</name> <t>The IPv4remoteRemote ASBRID sub-TLV,Identifier sub-TLV is defined for inclusion in theinter-AS reachabilityInter-AS Reachability Information TLV when advertising inter-AS links. The IPv4remoteRemote ASBRIDIdentifier sub-TLV specifies the IPv4 identifier of the remote ASBR to which the advertised inter-AS link connects. The value advertised is selected as defined in <xreftarget="_RID"/>.</t>target="_RID" format="default"/>.</t> <t>The IPv4remoteRemote ASBRIDIdentifier sub-TLV is TLV type 25 (seeSection 6.2)<xref target="sub-tlv-inter-as" format="default"/>) and is 4 octets in length. The format of the IPv4remoteRemote ASBRIDIdentifier sub-TLV is as follows:</t><t><figure> <artwork><![CDATA[<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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Remote ASBRIDIdentifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]></artwork></figure>The<t>The IPv4remoteRemote ASBRIDIdentifier sub-TLVMUST<bcp14>MUST</bcp14> be included if the neighboring ASBR has an IPv4 address.The value advertised is selected as defined in <xref target="_RID"/>.If the neighboring ASBR does not have an IPv4 address, the IPv6remoteRemote ASBRIDIdentifier sub-TLVMUST<bcp14>MUST</bcp14> be included instead. An IPv4remoteRemote ASBRIDIdentifier sub-TLV and IPv6remoteRemote ASBRIDIdentifier sub-TLVMAY<bcp14>MAY</bcp14> both be present in an extended IS reachability TLV.</t> </section> <sectiontitle="IPv6numbered="true" toc="default" anchor="ipv6-remote"> <name>IPv6 Remote ASBRID Sub-TLV"> <t>A new sub-TLV, which is referred to as theIdentifier Sub-TLV</name> <t>The IPv6remoteRemote ASBRID sub-TLV,Identifier sub-TLV is defined for inclusion in theinter-AS reachabilityInter-AS Reachability Information TLV when advertising inter-AS links. The IPv6remoteRemote ASBRIDIdentifier sub-TLV specifies the IPv6 identifier of the remote ASBR to which the advertised inter-AS link connects. The value advertised is selected as defined in <xreftarget="_RID"/>.</t>target="_RID" format="default"/>.</t> <t>The IPv6remoteRemote ASBRIDIdentifier sub-TLV is TLV type 26 (seeSection 6.2)<xref target="sub-tlv-inter-as" format="default"/>) and is 16 octets in length. The format of the IPv6remoteRemote ASBRIDIdentifier sub-TLV is as follows:</t><t><figure> <artwork><![CDATA[<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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Remote ASBRIDIdentifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Remote ASBRIDIdentifier (continued) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Remote ASBRIDIdentifier (continued) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Remote ASBRIDIdentifier (continued) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]></artwork></figure>The<t>The IPv6remoteRemote ASBRIDIdentifier sub-TLVMUST<bcp14>MUST</bcp14> be included if the neighboring ASBR has an IPv6 address. If the neighboring ASBR does not have an IPv6 address, the IPv4remoteRemote ASBRIDIdentifier sub-TLVMUST<bcp14>MUST</bcp14> be included instead. An IPv4remoteRemote ASBRIDIdentifier sub-TLV and IPv6remoteRemote ASBRIDIdentifier sub-TLVMAY<bcp14>MAY</bcp14> both be present in an extended IS reachability TLV.</t> </section> <sectiontitle="IPv6numbered="true" toc="default" anchor="ipv6-local"> <name>IPv6 Local ASBRID sub-TLV">Identifier Sub-TLV</name> <t>The IPv6 Local ASBRIDIdentifier sub-TLV is defined for inclusion in the Inter-AS Reachability Information TLV when advertising inter-AS links. The IPv6 Local ASBR Identifier sub-TLV specifies the IPv6 identifier of the remote ASBR to which the advertised inter-AS link connects. The value advertised is selected as defined in <xref target="_RID" format="default"/>.</t> <t>The IPv6 Local ASBR Identifier sub-TLV is TLV typeTBD145 (seeSection 6.3)<xref target="sub-tlv-inter-as" format="default"/>) and is 16 octets in length. The format of the IPv6 Local ASBRIDIdentifier sub-TLV is as follows:</t><figure> <artwork><![CDATA[<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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Local ASBRIDIdentifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Local ASBRIDIdentifier (continued) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Local ASBRIDIdentifier (continued) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Local ASBRIDIdentifier (continued) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]></artwork></figure> <t>The value advertised is selected as defined in <xref target="_RID"/>.</t><t>If the originating node does not support IPv4, the IPv6 Local ASBRIDIdentifier sub-TLVMUST<bcp14>MUST</bcp14> be present in theinter-AS reachabilityInter-AS Reachability Information TLV. Inter-ASreachabilityReachability Information TLVswhichthat have a Router ID of 0.0.0.0 and do not have the IPv6 Local ASBRIDIdentifier sub-TLV presentMUST<bcp14>MUST</bcp14> be ignored.</t> </section> </section> <sectiontitle="Sub-TLVsnumbered="true" toc="default"> <name>Sub-TLVs for IS-IS RouterCapability TLV">CAPABILITY TLV</name> <sectiontitle="IPv4numbered="true" toc="default"> <name>IPv4 TE Router IDsub-TLV">Sub-TLV</name> <t>The IPv4 TE Router ID sub-TLV is TLV type 11 (seeSection 6.3)<xref target="sub-tlv-is-is" format="default"/>) and is 4 octets in length. The format of the IPv4 TE Router ID sub-TLV is as follows:</t><t><figure> <artwork><![CDATA[0<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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TE Router ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]></artwork></figure></t><t>The value advertised is selected as defined in <xreftarget="_RID"/>.</t>target="_RID" format="default"/>.</t> <t>When the TE Router ID is needed to reach all routers within an entire IS-IS routing domain, the IS-IS RoutercapabilityCAPABILITY TLVMUST<bcp14>MUST</bcp14> be included in its LSP. If an ASBR supports Traffic Engineering for IPv4 and if the ASBR has an IPv4 TE Router ID, the IPv4 TE Router ID sub-TLVMUST<bcp14>MUST</bcp14> be included. If the ASBR does not have an IPv4 TE Router ID, the IPv6 TE Router ID sub-TLVMUST<bcp14>MUST</bcp14> be included instead. An IPv4 TE Router ID sub-TLV and IPv6 TE Router ID sub-TLVMAY<bcp14>MAY</bcp14> both be present in an IS-ISrouter capabilityRouter CAPABILITY TLV.</t> </section> <sectiontitle="IPv6numbered="true" toc="default"> <name>IPv6 TE Router IDsub-TLV">Sub-TLV</name> <t>The IPv6 TE Router ID sub-TLV is TLV type 12 (seeSection 6.3)<xref target="sub-tlv-is-is" format="default"/>) and is 16 octets in length. The format of the IPv6 TE Router ID sub-TLV is as follows:</t><t><figure> <artwork><![CDATA[0<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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TE Router ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TE Router ID (continued) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TE Router ID (continued) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TE Router ID (continued) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]></artwork></figure></t><t>The value advertised is selected as defined in <xreftarget="_RID"/>.</t>target="_RID" format="default"/>.</t> <t>When the TE Router ID is needed to reach all routers within an entire IS-IS routing domain, the IS-ISrouter capabilityRouter CAPABILITY TLVMUST<bcp14>MUST</bcp14> be included in its LSP. If an ASBR supports Traffic Engineering for IPv6 and if the ASBR has an IPv6 TE Router ID, the IPv6 TE Router ID sub-TLVMUST<bcp14>MUST</bcp14> be included. If the ASBR does not have an IPv6 TE Router ID, the IPv4 TE Router ID sub-TLVMUST<bcp14>MUST</bcp14> be included instead. An IPv4 TE Router ID sub-TLV and IPv6 TE Router ID sub-TLVMAY<bcp14>MAY</bcp14> both be present in an IS-ISrouter capabilityRouter CAPABILITY TLV.</t> </section> </section> </section> <section anchor="_Procedure"title="Procedurenumbered="true" toc="default"> <name>Procedure for Inter-AS TELinks">Links</name> <t>When TE is enabled on an inter-AS link and the link is up, the ASBRSHOULD<bcp14>SHOULD</bcp14> advertise this link using the normal procedures for <xreftarget="RFC5305"/>.target="RFC5305" format="default"/>. When either the link is down or TE is disabled on the link, the ASBRSHOULD<bcp14>SHOULD</bcp14> withdraw the advertisement. When there are changes to the TE parameters for the link (for example, when the available bandwidth changes), the ASBRSHOULD<bcp14>SHOULD</bcp14> re-advertise the link butMUST<bcp14>MUST</bcp14> take precautions against excessive re-advertisements.</t> <t>HellosMUST NOT<bcp14>MUST NOT</bcp14> be exchanged over the inter-AS link, and consequently, an IS-IS adjacencyMUST NOT<bcp14>MUST NOT</bcp14> be formed.</t> <t>The information advertised comes from the ASBR's knowledge of the TE capabilities of the link, the ASBR's knowledge of the current status and usage of the link, and configuration at the ASBR of theremoteRemote ASnumberNumber and remote ASBR TE Router ID.</t> <t>Legacy routers receiving an advertisement for an inter-AS TE link are able to ignore it because they do not know thenewTLV and sub-TLVs that are defined inSection 3<xref target="_SOL" format="default"/> of this document. They will continue to flood theLSP,LSP but will not attempt to use the information received.</t> <t>In the current operation ofISIS-TE,IS-IS TE, the LSRs at each end of a TE link emit LSPs describing the link. The databases in the LSRs then have two entries (one locally generated, the other from the peer) that describe the different 'directions' of the link. This enables Constrained Shortest Path First (CSPF) to do a two-way check on the link when performing path computation and eliminate it from consideration unless both directions of the link satisfy the required constraints.</t> <t>In the case we are considering here (i.e., of a TE link to another AS), there is, by definition, no IGP peering and hence no bidirectional TE link information. In order for the CSPF route computation entity to include the link as a candidate path, we have to find a way to get LSPs describing its (bidirectional) TE properties into the TE database.</t> <t>This is achieved by the ASBR advertising, internally to its AS, information about both directions of the TE link to the next AS. The ASBR will normally generate an LSP describing its own side of a link;herehere, we have it 'proxy' for the ASBR at the edge of the other AS and generate an additional LSP that describes that device's 'view' of the link.</t> <t>Only some essential TE information for the link needs to beadvertised;advertised, i.e., the Interface Address, theremoteRemote ASnumber,Number, and theremoteRemote ASBRIDIdentifier of an inter-AS TE link.</t> <t>Routers or PCEs that are capable of processing advertisements of inter-AS TE linksSHOULD NOT<bcp14>SHOULD NOT</bcp14> use such links to compute paths that exit an AS to a remote ASBR and then immediately re-enter the AS through another TE link. Such paths would constitute extremely rare occurrences andSHOULD NOT<bcp14>SHOULD NOT</bcp14> be allowed except as the result of specific policy configurations at the router or PCE computing the path.</t> <sectiontitle="Originnumbered="true" toc="default" anchor="te-info"> <name>Origin of Proxied TEInformation"> <t>Section 4Information</name> <t><xref target="_Procedure" format="default"/> describes how an ASBR advertises TE link information as a proxy for its neighborASBR,ASBR but does not describe where this information comes from.</t> <t>Although the source of the information described inSection 4<xref target="_Procedure" format="default"/> is outside the scope of this document, it is possible that it will be a configuration requirement at the ASBR, as are other local properties of the TE link. Further, where BGP is used to exchange IP routing information between the ASBRs, a certain amount of additional local configuration about the link and the remote ASBR is likely to be available.</t> <t>We note further that it is possible, and may be operationally advantageous, to obtain some of the required configuration information from BGP. Whether and how to utilize these possibilities is an implementation matter.</t> </section> </section> <section anchor="Security"title="Security Considerations">numbered="true" toc="default"> <name>Security Considerations</name> <t>The protocol extensions defined in this document are relatively minor and can be secured within the AS in which they are used by the existing IS-IS security mechanisms (e.g., using the cleartext passwords or Hashed Message Authentication Codes, which are defined in <xreftarget="RFC1195"/>,target="RFC1195" format="default"/>, <xreftarget="RFC5304"/>,target="RFC5304" format="default"/>, and <xreftarget="RFC5310"/>target="RFC5310" format="default"/> separately).</t> <t>There is no exchange of information betweenASes,ASes and no change to the IS-IS security relationship between the ASes. In particular, since no IS-IS adjacency is formed on the inter-AS links, there is no requirement for IS-IS security between the ASes.</t> <t>Some of the information included in thesenewadvertisements (e.g., theremoteRemote ASnumberNumber and theremoteRemote ASBRID)Identifier) is obtained manually from a neighboring administration as part of a commercial relationship. The source and content of this information should be carefully checked before it is entered as configuration information at the ASBR responsible for advertising the inter-AS TE links.</t> <t>It is worth notingthatthat, in the scenario we are considering, a Border Gateway Protocol (BGP) peering may exist between the two ASBRs and that this could be used to detect inconsistencies in configuration (e.g., the administration that originally supplied the information may provide incorrect information, or some manualmis-configurationsmisconfigurations or mistakes may be made by the operators). For example, if a differentremoteRemote ASnumberNumber is received in a BGP OPEN <xreftarget="RFC4271"/>target="RFC4271" format="default"/> from that locally configured toISIS-TE,IS-IS TE, as we describe here, then local policySHOULD<bcp14>SHOULD</bcp14> be applied to determine whether to alert the operator to a potentialmis-configurationmisconfiguration or to suppress the IS-IS advertisement of the inter-AS TE link. Advertisement of incorrect information could result in an inter-AS TE LSP that traverses an unintended AS. Note furtherthatthat, if BGP is used to exchange TE information as described inSection 4.1,<xref target="te-info" format="default"/>, the inter-AS BGP sessionSHOULD<bcp14>SHOULD</bcp14> be secured using mechanisms such as described in <xreftarget="RFC5925"/>target="RFC5925" format="default"/> to provide authentication and integrity checks.</t> <t>For a discussion of general security considerations for IS-IS, see <xreftarget="RFC5304"/>.</t>target="RFC5304" format="default"/>.</t> </section> <section anchor="IANA"title="IANA Considerations"> <t>IANA is requested to make the following allocations from registries under its control.</t>numbered="true" toc="default"> <name>IANA Considerations</name> <sectiontitle="Inter-ASnumbered="true" toc="default" anchor="inter-as-reachability"> <name>Inter-AS ReachabilityTLV"> <t>This document definesInformation TLV</name> <t>IANA has registered the followingnewIS-IS TLV type, described inSection 3.1, which has been registered<xref target="_RID" format="default"/>, in theIS-IS"IS-IS Top-Level TLVcodepointCodepoints" registry:</t><t><figure> <artwork><![CDATA[ Type Description IIH LSP SNP Purge Reference ---- ---------------------- --- --- --- ----- --------- 141 inter-AS reachability n y n n [This.I-D] information ]]></artwork> </figure></t><table align="center"> <thead> <tr> <th>Value</th> <th>Name</th> <th>IIH</th> <th>LSP</th> <th>SNP</th> <th>Purge</th> <th>Reference</th> </tr> </thead> <tbody> <tr> <td>141</td> <td>Inter-AS Reachability Information</td> <td>n</td> <td>y</td> <td>n</td> <td>n</td> <td>RFC 9346</td> </tr> </tbody> </table> </section> <sectiontitle="Sub-TLVsnumbered="true" toc="default" anchor="sub-tlv-inter-as"> <name>Sub-TLVs for the Inter-AS ReachabilityTLV"> <t>This document definesInformation TLV</name> <t>IANA has registered the followingnewsub-TLV types(described in Sections 3.3.1, 3.3.2, 3.3.3, and, 3.3.4)of top-level TLV 141 (seeSection 6.1 above). Three of these sub-TLVs have been registered<xref target="inter-as-reachability" format="default"/>) in theIS-IS"IS-IS Sub-TLVs for TLVs Advertising NeighborInformation registry byInformation" registry. These sub-TLVs are described in Sections <xreftarget="RFC5316"/>. One additional sub-TLV (IPv6 local ASBR identifier) is introduced by this documenttarget="remote-as" format="counter"/>, <xref target="ipv4-remote" format="counter"/>, <xref target="ipv6-remote" format="counter"/>, andneeds to be added to the same registry.<xref target="ipv6-local" format="counter"/>. </t><t><figure> <artwork><![CDATA[ Type Description 22 23 25 141 222 223 Reference ---- ----------------------------- --- --- --- --- --- --- --------- 24 remote AS number n n n y n n [This.I-D] 25 IPv4 remote<table align="center"> <thead> <tr> <th>Value</th> <th>Description</th> <th>22</th> <th>23</th> <th>25</th> <th>141</th> <th>222</th> <th>223</th> <th>Reference</th> </tr> </thead> <tbody> <tr> <td>24</td> <td>Remote AS Number</td> <td>n</td> <td>n</td> <td>n</td> <td>y</td> <td>n</td> <td>n</td> <td>RFC 9346</td> </tr> <tr> <td>25</td> <td>IPv4 Remote ASBRidentifier n n n y n n [This.I-D] 26 IPv6 remoteIdentifier</td> <td>n</td> <td>n</td> <td>n</td> <td>y</td> <td>n</td> <td>n</td> <td>RFC 9346</td> </tr> <tr> <td>26</td> <td>IPv6 Remote ASBRidentifier n n n y n n [This.I-D] TBD1 IPv6 localIdentifier</td> <td>n</td> <td>n</td> <td>n</td> <td>y</td> <td>n</td> <td>n</td> <td>RFC 9346</td> </tr> <tr> <td>45</td> <td>IPv6 Local ASBRidentifier n n n y n n [This.I-D] ]]></artwork> </figure>AsIdentifier</td> <td>n</td> <td>n</td> <td>n</td> <td>y</td> <td>n</td> <td>n</td> <td>RFC 9346</td> </tr> </tbody> </table> <t>As describedaboveinSection 3.1,<xref target="_RID" format="default"/>, the sub-TLVswhichthat are defined in <xreftarget="RFC5305"/>,target="RFC5305" format="default"/>, <xreftarget="RFC6119"/>target="RFC6119" format="default"/>, and other documents for describing the TE properties of a TE link are applicable to describe an inter-AS TE link andMAY<bcp14>MAY</bcp14> be included in theinter-AS reachabilityInter-AS Reachability Information TLV when adverting inter-AS TE links.</t> </section> <sectiontitle="Sub-TLVsnumbered="true" toc="default" anchor="sub-tlv-is-is"> <name>Sub-TLVs for the IS-IS RouterCapability TLV"> <t>This document definesCAPABILITY TLV</name> <t>IANA has registered the followingnewsub-TLVtypes, described in Sections 3.4.1 and 3.4.2,types of top-level TLV 242(which is defined in(see <xreftarget="RFC7981"/>) that have been registeredtarget="RFC7981" format="default"/>) in theIS-IS"IS-IS Sub-TLVs for IS-IS Router CAPABILITYTLV registry:</t> <t><figure> <artwork><![CDATA[Type Description Reference ---- ------------------------------ --------- 11 IPv4 TE Router ID [This.I-D] 12 IPv6 TE Router ID [This.I-D] ]]></artwork> </figure></t> </section> </section> <section title="Acknowledgements"> <t>For the original version ofTLV" registry. These sub-TLVs are described in Sections <xreftarget="RFC5316"/> the authors thanked Adrian Farrel, Jean-Louis Le Roux, Christian Hopps,target="remote-as" format="counter"/> andHannes Gredler for their review and comments on this document.</t><xref target="ipv4-remote" format="counter"/>. </t> <table align="center"> <thead> <tr> <th>Type</th> <th>Description</th> <th>Reference</th> </tr> </thead> <tbody> <tr> <td>11</td> <td>IPv4 TE Router ID</td> <td>RFC 9346</td> </tr> <tr> <td>12</td> <td>IPv6 TE Router ID</td> <td>RFC 9346</td> </tr> </tbody> </table> </section> </section> </middle> <back><references title="Normative References"> <?rfc include='reference.RFC.2119'?> <?rfc include='reference.RFC.1195'?> <?rfc include='reference.RFC.4271'?> <?rfc include='reference.RFC.5305'?> <?rfc include='reference.RFC.5308'?> <?rfc include='reference.RFC.5925'?> <?rfc include='reference.RFC.6119'?> <?rfc include='reference.RFC.7981'?> <?rfc include='reference.RFC.8174'?><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.1195.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4271.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5305.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5308.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5925.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6119.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7981.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/> </references> <references> <name>Informative References</name> <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.4216.xml"/> <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.5307.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5152.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5316.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5304.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5310.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.5441.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6823.xml"/> </references><references title="Informative References"> <?rfc include='reference.RFC.3209'?> <?rfc include='reference.RFC.4216'?> <?rfc include='reference.RFC.4655'?> <?rfc include='reference.RFC.5307'?> <?rfc include='reference.RFC.5152'?> <?rfc include='reference.RFC.5316'?> <?rfc include='reference.RFC.5304'?> <?rfc include='reference.RFC.5310'?> <?rfc include='reference.RFC.5441'?> <?rfc include='reference.RFC.6823'?></references> <sectiontitle="Changesnumbered="true" toc="default"> <name>Changes to RFC5316">5316</name> <t>The following is a summary of the substantive changes this document makes to RFC 5316. Some editorial changes were also made.</t> <t>RFC 5316 only allowed a32 bit32-bit Router ID in the fixed header of TLV 141. This is problematic in an IPv6-only deployment where an IPv4 address may not be available. This document specifies:</t><t>1. The<ol type="1"> <li>The Router ID should be identical to the value advertised in the Traffic EngineeringRouterrouter ID TLV (134) ifavailable.</t> <t>2. Ifavailable.</li> <li>If no Traffic Engineering Router ID isassignedassigned, the Router ID should be identical to an IP Interface Address[RFC1195]<xref target="RFC1195" format="default"/> advertised by the originatingIS.</t> <t>3. IfIS.</li> <li>If the originating node does not support IPv4, then the reserved value 0.0.0.0 must be used in the Router ID field and thenewIPv6 Local ASBRidentifierIdentifier sub-TLV must be present in theTLV.</t>TLV.</li> </ol> </section> <section numbered="false" toc="default"> <name>Acknowledgements</name> <t>In the previous version of this document <xref target="RFC5316" format="default"/>, the authors thanked <contact fullname="Adrian Farrel"/>, <contact fullname="Jean-Louis Le Roux"/>, <contact fullname="Christian Hopps"/>, and <contact fullname="Hannes Gredler"/> for their review and comments.</t> </section> </back> </rfc>