<?xml version="1.0"encoding="US-ASCII"?> <!-- This template is for creating an Internet Draft using xml2rfc, which is available here: http://xml.resource.org. -->encoding="UTF-8"?> <!DOCTYPE rfc SYSTEM"rfc2629.dtd"> <?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?> <!-- used by XSLT processors --> <!-- For a complete list and description of processing instructions (PIs), please see http://xml.resource.org/authoring/README.html. --> <!-- Below are generally applicable Processing Instructions (PIs) that most I-Ds might want to use. (Here they are set differently than their defaults in xml2rfc v1.32) --> <?rfc strict="yes" ?> <!-- give errors regarding ID-nits and DTD validation --> <!-- control the table of contents (ToC) --> <?rfc toc="yes"?> <!-- generate a ToC --> <?rfc tocdepth="4"?> <!-- the number of levels of subsections in ToC. default: 3 --> <!-- control references --> <?rfc symrefs="yes"?> <!-- use symbolic references tags, i.e, [RFC2119] instead of [1] --> <?rfc sortrefs="yes" ?> <!-- sort the reference entries alphabetically --> <!-- control vertical white space (using these PIs as follows is recommended by the RFC Editor) --> <?rfc compact="yes" ?> <!-- do not start each main section on a new page --> <?rfc subcompact="no" ?> <!-- keep one blank line between list items --> <!-- end of list of popular I-D processing instructions -->"rfc2629-xhtml.ent"> <rfccategory="std"xmlns:xi="http://www.w3.org/2001/XInclude" docName="draft-ietf-idr-bgp-ls-segment-routing-msd-18"ipr="trust200902">number="8814" ipr="trust200902" obsoletes="" updates="" submissionType="IETF" category="std" consensus="true" xml:lang="en" tocInclude="true" tocDepth="4" symRefs="true" sortRefs="true" version="3"> <front> <title abbrev="Signaling MSD using BGP-LS">SignalingMSD (MaximumMaximum SIDDepth) usingDepth (MSD) Using the Border Gateway Protocol - Link State</title> <seriesInfo name="RFC" value="8814"/> <author fullname="Jeff Tantsura"initials="J.T."initials="J" surname="Tantsura"> <organization>Apstra, Inc.</organization> <address> <email>jefftant.ietf@gmail.com</email> </address> </author> <author fullname="Uma Chunduri"initials="U.C."initials="U" surname="Chunduri"> <organization>Futurewei Technologies</organization> <address> <email>umac.ietf@gmail.com</email> </address> </author> <author fullname="Ketan Talaulikar"initials="K.T."initials="K" surname="Talaulikar"> <organization>Cisco Systems</organization> <address> <email>ketant@cisco.com</email> </address> </author> <author fullname="Greg Mirsky"initials="G.M."initials="G" surname="Mirsky"> <organization>ZTE Corp.</organization> <address> <email>gregimirsky@gmail.com</email> </address> </author> <author fullname="Nikos Triantafillis"initials="N.T."initials="N" surname="Triantafillis"> <organization>Amazon Web Services</organization> <address> <email>nikost@amazon.com</email> </address> </author> <dateyear=""/>year="2020" month="August" /> <area>Routing</area> <workgroup>IDR Working Group</workgroup><keyword>Internet-Draft</keyword><keyword>BGP-LS</keyword> <keyword>SID</keyword> <keyword>MSD</keyword> <keyword>SR</keyword> <abstract> <t>This document defines a way for a Border Gateway Protocol - Link State (BGP-LS) speaker to advertise multiple types of supported Maximum SID Depths (MSDs) at node and/or link granularity.</t> <t>Such advertisements allow entities (e.g., centralized controllers) to determine whether a particular Segment Identifier (SID) stack can be supported in a given network.</t> </abstract> </front> <middle> <section anchor="intro"title="Introduction">numbered="true" toc="default"> <name>Introduction</name> <t>When Segment Routing (SR) <xreftarget="RFC8402"/>target="RFC8402" format="default"/> paths are computed by a centralized controller, it is critical that the controller learns the Maximum SID Depth (MSD) that can be imposed at each node/link on a given SR path. This ensures that the Segment Identifier (SID) stack depth of a computed path doesn't exceed the number of SIDs the node is capable of imposing.</t> <t><xreftarget="RFC8664"/>target="RFC8664" format="default"/> defines how to signal MSD in the Path Computation Element Protocol (PCEP). The OSPF and IS-IS extensions for the signaling of MSD are defined in <xreftarget="RFC8476"/>target="RFC8476" format="default"/> and <xreftarget="RFC8491"/>target="RFC8491" format="default"/>, respectively.</t> <t>However, if PCEP is not supported/configured on the head-end ofaan SR tunnel or a Binding-SID anchor node, and the controller does not participate in IGP routing, it has no way of learning the MSD of nodes and links. BGP-LS <xreftarget="RFC7752"/>target="RFC7752" format="default"/> defines a way to expose topology and associated attributes and capabilities of the nodes in that topology to a centralized controller. </t> <t>This document defines extensions to BGP-LS to advertise one or more types of MSDs at node and/or link granularity. Other types ofMSDMSDs are known to be useful. For example, <xreftarget="I-D.ietf-ospf-mpls-elc"/>target="I-D.ietf-ospf-mpls-elc" format="default"/> and <xreftarget="I-D.ietf-isis-mpls-elc"/>target="I-D.ietf-isis-mpls-elc" format="default"/> define Entropy Readable Label DepthCapability (RLDC) that(ERLD), which is used by a head-end to insert an Entropy Label (EL) at a depth that can be read by transit nodes.</t> <t>In the future, it is expected that new MSD-Types will be defined to signal additional capabilities, e.g., ELs, SIDs that can be imposed through recirculation, or SIDs associated with another data plane such as IPv6. MSD advertisements may be useful even if SR itself is not enabled. For example, in a non-SR MPLS network, MSD defines the maximum label depth.</t> <sectiontitle="Conventions usednumbered="true" toc="default"> <name>Conventions Used inthis document">This Document</name> <sectiontitle="Terminology"> <t>MSD: Maximumnumbered="true" toc="default"> <name>Terminology</name> <dl newline="false"> <dt>MSD:</dt> <dd>Maximum SID Depth - the number of SIDs supported by a node or a link on anode</t> <t>PCE: Pathnode</dd> <dt>PCE:</dt> <dd>Path ComputationElement</t> <t>PCEP: PathElement</dd> <dt>PCEP:</dt> <dd>Path Computation ElementProtocol</t> <t>SID: SegmentProtocol</dd> <dt>SID:</dt> <dd>Segment Identifier as defined in <xreftarget="RFC8402"/></t> <t>SR: Segment Routing</t> <t>Label Imposition: Impositiontarget="RFC8402" format="default"/></dd> <dt>SR:</dt> <dd>Segment Routing</dd> <dt>Label Imposition:</dt> <dd> <t>Imposition is the act of modifying and/or adding labels to the outgoing label stack associated with a packet. Thisincludes:<list style="symbols"> <t>replacingincludes:</t> <ul spacing="normal"> <li>replacing the label at the top of the label stack with a newlabel.</t> <t>pushinglabel </li> <li>pushing one or more new labels onto the labelstack.</t>stack </li> </ul> <t>The number of labels imposed is then the sum of the number of labels that are replaced and the number of labels that are pushed. See <xreftarget="RFC3031"/>target="RFC3031" format="default"/> for further details.</t></list></t></dd></dl> </section> <sectiontitle="Requirements Language">numbered="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 inBCP 14BCP 14 <xreftarget="RFC2119"/>target="RFC2119" format="default"/> <xreftarget="RFC8174"/>target="RFC8174" format="default"/> when, and only when, they appear in all capitals, as shownhere .</t>here.</t> </section> </section> </section> <section anchor="ADVT"title="Advertisementnumbered="true" toc="default"> <name>Advertisement of MSD viaBGP-LS">BGP-LS</name> <t>This document describes extensions that enable BGP-LS speakers to signal the MSD capabilities(<xref target="RFC8491"/> )<xref target="RFC8491" format="default"/> of nodes and their links in a network to a BGP-LS consumer of network topology such as a centralized controller. The centralized controller can leverage this information in computation of SR paths based on their MSD capabilities. When a BGP-LS speaker is originating the topology learnt via link-state routing protocols such as OSPF or IS-IS, the MSD information for the nodes and their links is sourced from the underlying extensions as defined in <xreftarget="RFC8476"/>target="RFC8476" format="default"/> and <xreftarget="RFC8491"/>target="RFC8491" format="default"/>, respectively. </t> <t> The extensions introduced in this document allow for advertisement of different MSD-Types, which are defined elsewhere and were introduced in <xreftarget="RFC8491"/>.target="RFC8491" format="default"/>. This enables sharing of MSD-Types that may be defined in the future by the IGPs in BGP-LS. </t> </section> <section anchor="NodeMSD"title="Nodenumbered="true" toc="default"> <name>Node MSDTLV">TLV</name> <t>The Node MSD (<xreftarget="RFC8476"/>target="RFC8476" format="default"/> <xreftarget="RFC8491"/>)target="RFC8491" format="default"/>) is encoded in a new Node Attribute TLV <xreftarget="RFC7752"/>target="RFC7752" format="default"/> to carry the provisioned SID depth of the router identified by the corresponding Router-ID. Node MSD is the smallest MSD supported by the node on the set of interfaces configured for use. MSD values may be learned via a hardware API or may be provisioned. The following format is used:</t> <figureanchor="node-attribute_tlv" title="Nodeanchor="node-attribute_tlv"> <name>Node MSD TLVFormat"> <artwork><![CDATA[Format</name> <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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MSD-Type | MSD-Value | MSD-Type... | MSD-Value... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]></artwork> </figure><t>Where:<list style="symbols"> <t>Type: 266</t> <t>Length: variable<t>Where:</t> <ul empty="true"> <li> <dl> <dt>Type:</dt><dd>266</dd> <dt>Length:</dt><dd>variable (multiple of 2); represents the total length of the value field inoctets.</t> <t>Value : consistsoctets.</dd> <dt>Value:</dt><dd><t>consists of one or more pairs of a 1-octet MSD-Type and 1-octetMSD-Value.<list style="symbols"> <t>MSD-Type : oneMSD-Value.</t> <dl> <dt>MSD-Type:</dt><dd>one of the values defined in the "IGP MSD-Types" registry defined in <xreftarget="RFC8491"/>.</t> <t>MSD-Value :target="RFC8491" format="default"/>.</dd> <dt>MSD-Value:</dt><dd> a number in the range of 0-255. For all MSD-Types, 0 represents the lack of ability to impose an MSD stack of any depth; any other value represents that of the node. This valueMUST<bcp14>MUST</bcp14> represent the lowest value supported by any link configured for use by the advertising protocolinstance.</t> </list></t> </list></t>instance.</dd> </dl> </dd> </dl> </li> </ul> </section> <section anchor="LinkMSD"title="Linknumbered="true" toc="default"> <name>Link MSDTLV">TLV</name> <t>The Link MSD (<xreftarget="RFC8476"/>target="RFC8476" format="default"/> <xreftarget="RFC8491"/>)target="RFC8491" format="default"/>) is defined to carry the MSD of the interface associated with the link. It is encoded in a new Link Attribute TLV <xreftarget="RFC7752"/>target="RFC7752" format="default"/> using the following format:</t> <figureanchor="link-attribute_tlv" title="Linkanchor="link-attribute_tlv"> <name>Link MSD TLVFormat"> <artwork><![CDATA[Format</name> <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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MSD-Type | MSD-Value | MSD-Type... | MSD-Value... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]></artwork> </figure><t>Where:<list style="symbols"> <t>Type: 267</t> <t>Length: variable<t>Where:</t> <ul empty="true"> <li> <dl> <dt>Type:</dt><dd> 267</dd> <dt>Length:</dt><dd>variable (multiple of 2); represents the total length of the value field inoctets.</t> <t>Value : consistsoctets.</dd> <dt>Value:</dt><dd><t>consists of one or more pairs of a 1-octet MSD-Type and 1-octetMSD-Value.<list style="symbols"> <t>MSD-Type : MSD-Type : oneMSD-Value.</t> <dl> <dt>MSD-Type:</dt><dd>one of the values defined in the "IGP MSD-Types" registry defined in <xreftarget="RFC8491"/>.</t> <t>MSD-Value : atarget="RFC8491" format="default"/>.</dd> <dt>MSD-Value:</dt><dd>a number in the range of 0-255. For all MSD-Types, 0 represents the lack of ability to impose an MSD stack of any depth; any other value represents that of the link when used as an outgoinginterface.</t> </list></t> </list></t>interface.</dd> </dl> </dd> </dl> </li> </ul> </section> <section anchor="iana-consider"title="IANA Considerations"> <t>This document requests assigning code-pointsnumbered="true" toc="default"> <name>IANA Considerations</name> <t>IANA has assigned code points from the registry "BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs" based on the tablebelow. Early allocation for these code-points have been done by IANA.</t> <figure> <artwork align="center"><![CDATA[ +------------+-----------------+---------------------------+-------------------+ | Code Point | Description | IS-IS TLV/Sub-TLV | Reference | +------------+-----------------+---------------------------+-------------------+ | 266 | Nodebelow.</t> <table anchor="iana-table"> <name>BGP-LS MSD| 242/23 | This document | | 267 | Link MSD | (22,23,25,141,222,223)/15 | This document | +------------+-----------------+---------------------------+-------------------+ ]]></artwork> </figure>TLV Code Points </name> <thead> <tr> <th>TLV Code Point</th> <th>Description</th> <th>IS-IS TLV/Sub-TLV</th> <th>Reference</th> </tr> </thead> <tbody> <tr> <td>266</td> <td>Node MSD</td> <td>242/23</td> <td>This document</td> </tr> <tr> <td>267</td> <td>Link MSD</td> <td>(22,23,25,141,222,223)/15</td> <td>This document</td> </tr> </tbody> </table> </section> <section anchor="Manageability"title="Manageability Considerations">numbered="true" toc="default"> <name>Manageability Considerations</name> <t>The new protocol extensions introduced in this document augment the existing IGP topology information that is distributed via <xreftarget="RFC7752"/>.target="RFC7752" format="default"/>. Procedures and protocol extensions defined in this document do not affect the BGP protocol operations and management other than as discussed inthe Manageability Considerations sectionSection <xref target="RFC7752" sectionFormat="bare" section="6">Manageability Considerations</xref> of <xref target="RFC7752"/>. Specifically, the malformed attribute tests for syntactic checks inthe Fault Management sectionSection <xref target="RFC7752" sectionFormat="bare" section="6.2.2">Fault Management</xref> of <xref target="RFC7752"/> now encompass the new BGP-LS Attribute TLVs defined in this document. The semantic or content checking for the TLVs specified in this document and their association with the BGP-LSNLRINetwork Layer Reachability Information (NLRI) types or their BGP-LS Attribute is left to the consumer of the BGP-LS information(e.g.(e.g., an application or a controller) and not the BGP protocol.</t> <t>A consumer of the BGP-LS information retrieves this information over a BGP-LS session (referSection 1to Sections <xref target="RFC7752" sectionFormat="bare" section="1"/> and2<xref target="RFC7752" sectionFormat="bare" section="2"/> of <xreftarget="RFC7752"/>).</t>target="RFC7752" format="default"/>).</t> <t>This document only introduces new AttributeTLVsTLVs, and any syntactic error in them would result in the BGP-LS Attribute being discarded <xreftarget="RFC7752"/>.target="RFC7752" format="default"/>. The MSD information introduced in BGP-LS by this specification, may be used by BGP-LS consumer applications likeaan SR PCE to learn the SR SID stack handling capabilities of the nodes in the topology. This can enable the SR PCE to perform path computations taking into consideration the size of SID stack that the specific head-end node may be able to impose. Errors in the encoding or decoding of the MSD information may result in the unavailability of such information to the SRPCEPCE, or incorrect information being made available to it. This may result in the head-end node not being able to instantiate the desired SR path in its forwarding and provide theSR basedSR-based optimization functionality. The handling of such errors by applications like SR PCE may be implementation specific and out of scope of this document.</t> <t> The extensions specified in this document do not specify any new configuration or monitoring aspects in BGP or BGP-LS. The specification of BGP models is an ongoing work based on the <xreftarget="I-D.ietf-idr-bgp-model"/>.</t>target="I-D.ietf-idr-bgp-model" format="default"/>.</t> </section> <section anchor="security"title="Security Considerations">numbered="true" toc="default"> <name>Security Considerations</name> <t>The advertisement of an incorrect MSD value may have negative consequences. If the value is smaller than supported, path computation may fail to compute a viable path. If the value is larger than supported, an attempt to instantiate a path that can't be supported by the head-end (the node performing the SID imposition) may occur. The presence of this information may also inform an attacker of how to induce any of the aforementioned conditions.</t> <t>The procedures and protocol extensions defined in this document do not affect the BGP security model. See the "Security Considerations"sectionSection of <xreftarget="RFC4271"/>target="RFC4271" format="default"/> for a discussion of BGP security. Also, refer to <xreftarget="RFC4272"/>target="RFC4272" format="default"/> and <xreftarget="RFC6952"/>target="RFC6952" format="default"/> for analyses of security issues for BGP. Security considerations for acquiring and distributing BGP-LS information are discussed in <xreftarget="RFC7752"/>.target="RFC7752" format="default"/>. The TLVs introduced in this document are used to propagate the MSD IGP extensions defined in <xreftarget="RFC8476"/>target="RFC8476" format="default"/> and <xreftarget="RFC8491"/>.target="RFC8491" format="default"/>. It is assumed that the IGP instances originating these TLVs will support all the required security (as described in <xreftarget="RFC8476"/>target="RFC8476" format="default"/> and <xreftarget="RFC8491"/>)target="RFC8491" format="default"/>) in order to prevent any security issues when propagating the TLVs into BGP-LS. The advertisement of the node and link attribute information defined in this document presents no significant additional risk beyond that associated with the existing node and link attribute information already supported in <xreftarget="RFC7752"/>.target="RFC7752" format="default"/>. </t> </section> </middle> <back> <displayreference target="I-D.ietf-idr-bgp-model" to="BGP-MODEL"/> <displayreference target="I-D.ietf-ospf-mpls-elc" to="OSPF-ELC"/> <displayreference target="I-D.ietf-isis-mpls-elc" to="ISIS-ELC"/> <references> <name>References</name> <references> <name>Normative References</name> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7752.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8476.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8491.xml"/> </references> <references> <name>Informative References</name> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3031.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8402.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8664.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4271.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4272.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6952.xml"/> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.ietf-idr-bgp-model.xml"/> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.ietf-ospf-mpls-elc.xml"/> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.ietf-isis-mpls-elc.xml"/> </references> </references> <sectionanchor="Contributors" title="Contributors"> <figure> <artwork><![CDATA[Siva Sivabalan Cisco Systems Inc. Canada Email: msiva@cisco.com]]></artwork> </figure> </section> <section title="Acknowledgements">numbered="false" toc="default"> <name>Acknowledgements</name> <t>We would like to thankAcee Lindem, Stephane Litkowski, Bruno Decraene and Alvaro Retana<contact fullname="Acee Lindem"/>, <contact fullname="Stephane Litkowski"/>, <contact fullname="Bruno Decraene"/>, and <contact fullname="Alvaro Retana"/> for their reviews and valuable comments.</t> </section></middle> <back> <references title="Normative References"> <?rfc include="reference.RFC.2119"?> <?rfc include="reference.RFC.7752"?> <?rfc include="reference.RFC.8174"?> <?rfc include="reference.RFC.8476"?> <?rfc include="reference.RFC.8491"?> </references> <references title="Informative References"> <?rfc include="reference.RFC.3031"?> <?rfc include="reference.RFC.8402"?> <?rfc include="reference.RFC.8664"?> <?rfc include="reference.RFC.4271"?> <?rfc include="reference.RFC.4272"?> <?rfc include="reference.RFC.6952"?> <?rfc include='reference.I-D.ietf-idr-bgp-model'?> <?rfc include="reference.I-D.ietf-ospf-mpls-elc"?> <?rfc include="reference.I-D.ietf-isis-mpls-elc"?> </references><section anchor="Contributors" numbered="false" toc="default"> <name>Contributors</name> <contact fullname="Siva Sivabalan"> <organization>Cisco Systems Inc.</organization> <address> <postal> <country>Canada</country> </postal> <email>msiva@cisco.com</email> </address> </contact> </section> </back> </rfc>