IDR Working Group J. Tantsura Internet-Draft Apstra, Inc. Intended status: Standards Track U. Chunduri Expires:August 23,December 3, 2019Huawei USAFuturewei Technologies K. Talaulikar Cisco Systems G. Mirsky ZTE Corp.S. Sivabalan CiscoN. Triantafillis Apstra, Inc.February 19,June 1, 2019 Signaling MSD (Maximum SID Depth) using Border Gateway Protocol Link- Statedraft-ietf-idr-bgp-ls-segment-routing-msd-04draft-ietf-idr-bgp-ls-segment-routing-msd-05 Abstract 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. Such advertisements allowlogically centralizedentities (e.g., centralized controllers) to determine whether a particularSIDSegment Identifier (SID) stack can be supported in a given network. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire onAugust 23,December 3, 2019. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Conventions used in this document . . . . . . . . . . . . 3 1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3 1.1.2. Requirements Language . . . . . . . . . . . . . . . .34 2.Problem StatementAdvertisement of MSD via BGP-LS . . . . . . . . . . . . . . . 4 3. Node MSD TLV . . . . . . .3 3. MSD supported by a node . .. . . . . . . . . . . . . . . . . 4 4. Link MSDsupported on a linkTLV . . . . . . . . . . . . . . . . . . .4. . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . .56 6. Security Considerations . . . . . . . . . . . . . . . . . . .56 7.AcknowledgementsContributors . . . . . . . . . . . . . . . . . . . . . .5. . 6 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . .5 8.1.7 9.1. Normative References . . . . . . . . . . . . . . . . . .5 8.2.7 9.2. Informative References . . . . . . . . . . . . . . . . .67 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . .78 1. Introduction When Segment Routingtunnels(SR) [RFC8402] paths are computed by a centralized controller, it is critical that the controller learns theMSD "MaximumMaximum SIDDepth" of the node or linkDepth (MSD) that can be imposed at each node/link on a given SRtunnel exits over, sopath. This ensures that theSIDSegment Identifier (SID) stack depth of apathcomputed path doesn't exceed the number of SIDs the node is capable of imposing.This document describes[I-D.ietf-pce-segment-routing] defines how touse BGP-LS tosignaltheMSDof a node or link to a centralized controller. PCEP SRin the Path Computation Element Protocol (PCEP). The OSPF and IS-IS extensionsdraft [I-D.ietf-pce-segment-routing] signalsfor signaling of MSD are defined inSR PCE Capability TLV[RFC8476] andMETRIC Object.[RFC8491] respectively. However, if PCEP is not supported/configured on the head-end of a SR tunnel or a Binding-SID anchornodenode, and controller does not participate in IGP routing, it has no wayto learnof learning the MSD of nodes andlinks which has been configured.links. BGP-LS [RFC7752] defines a way toexposeadvertise topology and associated attributes and capabilities of the nodes in that topology to a centralized controller. This document defines extensions to BGP-LS to advertise one or more types of MSDs at node and/or link granularity. Other types of MSD are known to be useful. For example, [I-D.ietf-ospf-mpls-elc] and [I-D.ietf-isis-mpls-elc] define Readable Label Depth Capability (RLDC) that is used by a head-end to insert an Entropy Label (EL) at a depth that can be read by transit nodes. 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. 1.1. Conventions used in this document 1.1.1. Terminology BGP-LS: Distribution of Link-State and TE Information using Border Gateway Protocol MSD: Maximum SID Depth PCC: Path Computation Client PCE: Path Computation Element PCEP: Path Computation Element Protocol SID: Segment Identifier SR: Segment routing Label Imposition: Imposition is the act of modifying and/or adding labels to the outgoing label stack associated with a packet. This includes: o replacing the label at the top of the label stack with a new label. o pushing one or more new labels onto the label stack 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 [RFC3031] for further details. 1.1.2. Requirements Language 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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here . 2.Problem Statement In existing technology only PCEP has extensionAdvertisement of MSD via BGP-LS This document describes extensions that enable BGP-LS speakers to signal the MSD(SR PCE Capability TLV/ METRIC Objectcapabilities of nodes and their links in a network to a BGP-LS consumer of network topology such asdefineda centralized controller. The centralized controller can leverage this information in[I-D.ietf-pce-segment-routing],If PCEP is not supported by the node (head-endcomputation oftheSRtunnel) controller has no way to learn thepaths and their instantiation on network nodes based on their MSDofcapabilities. When a BGP-LS speaker is originating thenode/link configured.topology learnt via link-state routing protocols like OSPF or IS-IS, the MSD information for the nodes andIS-IStheir links is sourced from the underlying extensionsareas definedin: [RFC8476],in [RFC8476] and [RFC8491]3.respectively. The BGP-LS speaker may also advertise the MSDsupported by ainformation for the local node and its links when not running any link-state IGP protocol e.g. when running BGP as the only routing protocol. The extensions introduced in this document allow for advertisement of different MSD-Types. This document does not define these MSD-Types but leverages the definition, guidelines and the code-point registry specified in [RFC8491]. This enables sharing of MSD-Types that may be defined in the future by the IGPs in BGP-LS. 3. Node MSD TLV Node MSD is encoded in a new Node AttributeTLV, as defined inTLV [RFC7752] using the following format: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Sub-Type and Value ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...MSD-Type | MSD-Value | MSD-Type... | MSD-Value... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Nodeattribute format Type : A 2-octet field specifying code-point of the newMSD TLVtype. Code-point:(TBD1) from BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs registryFormat Where: o Type: 266 o Length:A 2-octet field that indicatesvariable (multiple of 2); represents the total length of the valueportion Sub-Typefield in octets. o Value : consists of one or more pairs of a 1-octet MSD-Type andvalue fields are as1-octet MSD-Value. * MSD-Type : one of the values defined incorresponding OSPF [RFC8476] and IS-IS [RFC8491] extensions. 4.the IANA registry titled "IGP MSD-Types" under the "Interior Gateway Protocol (IGP) Parameters" registry created by [RFC8491]. * MSD-Value : 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 value MUST represent the lowest value supportedon aby any link configured for use by the advertising protocol instance. 4. Link MSD TLV Link MSD is encoded in aNewnew Link AttributeTLV, as defined inTLV [RFC7752] using the following format: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Sub-Type and Value ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...MSD-Type | MSD-Value | MSD-Type... | MSD-Value... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Linkattribute format Type : A 2-octet field specifying code-point of the newMSD TLVtype. Code-point:(TBD2) from BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs registryFormat Where: o Type: 267 o Length:A 2-octet field that indicatesvariable (multiple of 2); represents the total length of the valueportion Sub-Typefield in octets. o Value : consists of one or more pairs of a 1-octet MSD-Type andvalue fields are as1-octet MSD-Value. * MSD-Type : one of the values defined incorresponding OSPF [RFC8476] and IS-IS [RFC8491] extensions.the IANA registry titled "IGP MSD-Types" under the "Interior Gateway Protocol (IGP) Parameters" registry created by [RFC8491]. * MSD-Value : 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 outgoing interface. 5. IANA ConsiderationsWe request IANA assign code pointsThis document requests assigning code-points from the registryBGP-LS"BGP- LS Node Descriptor, Link Descriptor, Prefix Descriptor, and AttributeTLVs, as follows: TLVTLVs" based on table below. Early allocation for these code-points have been done by IANA. +------------+-----------------+---------------------------+ | Code Point | Description | IS-IS TLV/Sub-TLVReference TBD1| +------------+-----------------+---------------------------+ | 266 | Node MSD | 242/23(this document) TBD2| | 267 | Link MSD | (22,23,25,141,222,223)/15(this document)| +------------+-----------------+---------------------------+ 6. Security Considerations 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. This document does not introduce security issues beyond those discussed in [RFC7752], [RFC8476] and [RFC8491] 7. Contributors Siva Sivabalan Cisco Systems Inc. Canada Email: msiva@cisco.com 8. Acknowledgements We like to thank Acee Lindem,Ketan Talaulikar,Stephane Litkowski and Bruno Decraene for their reviews and valuable comments.8.9. References8.1.9.1. Normative References[I-D.ietf-pce-segment-routing] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W., and J. Hardwick, "PCEP Extensions for Segment Routing", draft-ietf-pce-segment-routing-15 (work in progress), February 2019.[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>. [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and S. Ray, "North-Bound Distribution of Link-State and Traffic Engineering (TE) Information Using BGP", RFC 7752, DOI 10.17487/RFC7752, March 2016, <https://www.rfc-editor.org/info/rfc7752>. [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>. [RFC8476] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak, "Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476, DOI 10.17487/RFC8476, December 2018, <https://www.rfc-editor.org/info/rfc8476>. [RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491, DOI 10.17487/RFC8491, November 2018, <https://www.rfc-editor.org/info/rfc8491>.8.2.9.2. Informative References [I-D.ietf-isis-mpls-elc] Xu, X., Kini, S.,Sivabalan, S.,Psenak, P., Filsfils, C., and S. Litkowski, "Signaling Entropy Label Capability and Entropy Readable Label Depth Using IS-IS", draft-ietf-isis-mpls-elc-06elc-07 (work in progress),September 2018. [I-D.ietf-isis-segment-routing-extensions] Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A., Gredler, H., and B. Decraene, "IS-IS Extensions for Segment Routing", draft-ietf-isis-segment-routing- extensions-22 (work in progress), December 2018.May 2019. [I-D.ietf-ospf-mpls-elc] Xu, X., Kini, S.,Sivabalan, S.,Psenak, P., Filsfils, C., and S. Litkowski, "Signaling Entropy Label Capability and Entropy Readable Label-stack Depth Using OSPF", draft-ietf-ospf-mpls-elc-07mpls-elc-08 (work in progress),September 2018. [I-D.ietf-ospf-segment-routing-extensions] Psenak, P., Previdi,May 2019. [I-D.ietf-pce-segment-routing] Sivabalan, S., Filsfils, C.,Gredler, H., Shakir, R.,Tantsura, J., Henderickx, W., and J.Tantsura, "OSPFHardwick, "PCEP Extensions for Segment Routing",draft-ietf-ospf-segment- routing-extensions-27draft-ietf-pce-segment-routing-16 (work in progress),December 2018. [I-D.ietf-spring-segment-routing-mpls] Bashandy,March 2019. [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, DOI 10.17487/RFC3031, January 2001, <https://www.rfc-editor.org/info/rfc3031>. [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routingwith MPLS data plane", draft-ietf-spring-segment-routing-mpls-18 (work in progress), December 2018.Architecture", RFC 8402, DOI 10.17487/RFC8402, July 2018, <https://www.rfc-editor.org/info/rfc8402>. Authors' Addresses Jeff Tantsura Apstra, Inc. Email: jefftant.ietf@gmail.com Uma ChunduriHuawei USAFuturewei Technologies Email: umac.ietf@gmail.com Ketan Talaulikar Cisco Systems Email:uma.chunduri@huawei.comketant@cisco.com Greg Mirsky ZTE Corp. Email: gregimirsky@gmail.comSiva Sivabalan Cisco Email: msiva@cisco.comNikos Triantafillis Apstra, Inc. Email: nikos@apstra.com