IDR Working Group J. Tantsura Internet-Draft Apstra, Inc. Intended status: Standards Track U. Chunduri Expires: August 23, 2019 Huawei USA G. Mirsky ZTE Corp. S. Sivabalan Cisco N. Triantafillis Apstra, Inc. February 19, 2019 Signaling MSD (Maximum SID Depth) using Border Gateway Protocol Link- State draft-ietf-idr-bgp-ls-segment-routing-msd-04 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 allow logically centralized entities (e.g., centralized controllers) to determine whether a particular 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 on August 23, 2019. Tantsura, et al. Expires August 23, 2019 [Page 1] Internet-DraftSignaling MSD (Maximum SID Depth) using BGP-LFebruary 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 . . . . . . . . . . . . . . . . 3 2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3 3. MSD supported by a node . . . . . . . . . . . . . . . . . . . 4 4. MSD supported on a link . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 8.1. Normative References . . . . . . . . . . . . . . . . . . 5 8.2. Informative References . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction When Segment Routing tunnels are computed by a centralized controller, it is critical that the controller learns the MSD "Maximum SID Depth" of the node or link SR tunnel exits over, so the SID stack depth of a path computed doesn't exceed the number of SIDs the node is capable of imposing. This document describes how to use BGP-LS to signal the MSD of a node or link to a centralized controller. PCEP SR extensions draft [I-D.ietf-pce-segment-routing] signals MSD in SR PCE Capability TLV and METRIC Object. However, if PCEP is not supported/configured on the head-end of a SR tunnel or a Binding-SID anchor node and controller does not participate in IGP routing, it has no way to learn the MSD of nodes and links which has been configured. BGP-LS [RFC7752] defines a way to expose topology and Tantsura, et al. Expires August 23, 2019 [Page 2] Internet-DraftSignaling MSD (Maximum SID Depth) using BGP-LFebruary 2019 associated attributes and capabilities of the nodes in that topology to a centralized controller. 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. 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 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 extension to signal the MSD (SR PCE Capability TLV/ METRIC Object as defined in [I-D.ietf-pce-segment-routing],If PCEP is not supported by the node (head-end of the SR tunnel) controller has no way to learn the MSD of the node/link configured. OSPF and IS-IS extensions are defined in: [RFC8476], [RFC8491] Tantsura, et al. Expires August 23, 2019 [Page 3] Internet-DraftSignaling MSD (Maximum SID Depth) using BGP-LFebruary 2019 3. MSD supported by a node Node MSD is encoded in a new Node Attribute TLV, as defined in [RFC7752] 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 ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... Figure 1: Node attribute format Type : A 2-octet field specifying code-point of the new TLV type. Code-point:(TBD1) from BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs registry Length: A 2-octet field that indicates the length of the value portion Sub-Type and value fields are as defined in corresponding OSPF [RFC8476] and IS-IS [RFC8491] extensions. 4. MSD supported on a link Link MSD is encoded in a New Link Attribute TLV, as defined in [RFC7752] 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 ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... Figure 2: Link attribute format Type : A 2-octet field specifying code-point of the new TLV type. Code-point:(TBD2) from BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs registry Length: A 2-octet field that indicates the length of the value portion Tantsura, et al. Expires August 23, 2019 [Page 4] Internet-DraftSignaling MSD (Maximum SID Depth) using BGP-LFebruary 2019 Sub-Type and value fields are as defined in corresponding OSPF [RFC8476] and IS-IS [RFC8491] extensions. 5. IANA Considerations We request IANA assign code points from the registry BGP-LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs, as follows: TLV Code Point Description IS-IS TLV/Sub-TLV Reference TBD1 Node MSD 242/23 (this document) TBD2 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. Acknowledgements We like to thank Acee Lindem, Ketan Talaulikar, Stephane Litkowski and Bruno Decraene for their reviews and valuable comments. 8. References 8.1. 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, . Tantsura, et al. Expires August 23, 2019 [Page 5] Internet-DraftSignaling MSD (Maximum SID Depth) using BGP-LFebruary 2019 [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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [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, . [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, . 8.2. Informative References [I-D.ietf-isis-mpls-elc] Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. Litkowski, "Signaling Entropy Label Capability and Entropy Readable Label Depth Using IS-IS", draft-ietf-isis-mpls- elc-06 (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. [I-D.ietf-ospf-mpls-elc] Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. Litkowski, "Signaling Entropy Label Capability and Entropy Readable Label-stack Depth Using OSPF", draft-ietf-ospf- mpls-elc-07 (work in progress), September 2018. [I-D.ietf-ospf-segment-routing-extensions] Psenak, P., Previdi, S., Filsfils, C., Gredler, H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF Extensions for Segment Routing", draft-ietf-ospf-segment- routing-extensions-27 (work in progress), December 2018. Tantsura, et al. Expires August 23, 2019 [Page 6] Internet-DraftSignaling MSD (Maximum SID Depth) using BGP-LFebruary 2019 [I-D.ietf-spring-segment-routing-mpls] Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing with MPLS data plane", draft-ietf-spring-segment-routing-mpls-18 (work in progress), December 2018. Authors' Addresses Jeff Tantsura Apstra, Inc. Email: jefftant.ietf@gmail.com Uma Chunduri Huawei USA Email: uma.chunduri@huawei.com Greg Mirsky ZTE Corp. Email: gregimirsky@gmail.com Siva Sivabalan Cisco Email: msiva@cisco.com Nikos Triantafillis Apstra, Inc. Email: nikos@apstra.com Tantsura, et al. Expires August 23, 2019 [Page 7]