IDR Working Group J. Tantsura Internet-Draft Individual Intended status: Standards Track U. Chunduri Expires: April 18, 2018 Huawei Technologies G. Mirsky ZTE Corp. S. Sivabalan Cisco October 15, 2017 Signaling Maximum SID Depth using Border Gateway Protocol Link-State draft-ietf-idr-bgp-ls-segment-routing-msd-01 Abstract This document proposes a way to signal Maximum SID Depth (MSD) supported by a node at node and/or link granularity by a BGP-LS speaker. In a Segment Routing (SR) enabled network a centralized controller that programs SR tunnels needs to know the MSD supported by the head-end at node and/or link granularity to push the SID stack of an appropriate depth. MSD is relevant to the head-end of a SR tunnel or Binding-SID anchor node where Binding-SID expansions might result in creation of a new SID stack. 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 April 18, 2018. Copyright Notice Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. Tantsura, et al. Expires April 18, 2018 [Page 1] Internet-Draft Signaling MSD Using BGP-LS October 2017 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 . . . . . . . . . . . . . . . . . . . . . . . 6 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 associated attributes and capabilities of the nodes in that topology to a centralized controller. MSD of sub-type 1, called Base MSD as defined in Section 3 is used to signal the number of SID's a node is capable of imposing, to be used Tantsura, et al. Expires April 18, 2018 [Page 2] Internet-Draft Signaling MSD Using BGP-LS October 2017 by a path computation element/controller. In case, there are additional labels (e.g. service) that are to be pushed to the stack - this would be signaled with an another MSD type (TBD), no adjustment to the Base MSD should be made. In the future, new MSD types could be defined to signal additional capabilities: entropy labels, labels that can be pushed thru recirculation, or another dataplane e.g IPv6. 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 [RFC2119]. 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: [I-D.ietf-ospf-segment-routing-msd] [I-D.ietf-isis-segment-routing-msd] Tantsura, et al. Expires April 18, 2018 [Page 3] Internet-Draft Signaling MSD Using BGP-LS October 2017 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 specifiying 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 [I-D.ietf-ospf-segment-routing-msd] and IS-IS [I-D.ietf-isis-segment-routing-msd] 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 specifiying 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 April 18, 2018 [Page 4] Internet-Draft Signaling MSD Using BGP-LS October 2017 Sub-Type and value fields are as defined in corresponding OSPF [I-D.ietf-ospf-segment-routing-msd] and IS-IS [I-D.ietf-isis-segment-routing-msd] 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 This document does not introduce security issues beyond those discussed in [RFC7752] 7. Acknowledgements We like to thank Nikos Triantafillis, Stephane Litkowski and Bruno Decraene for their reviews and valuable comments. 8. References 8.1. Normative References [I-D.ietf-isis-segment-routing-msd] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg, "Signaling MSD (Maximum SID Depth) using IS-IS", draft- ietf-isis-segment-routing-msd-04 (work in progress), June 2017. [I-D.ietf-ospf-segment-routing-msd] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak, "Signaling MSD (Maximum SID Depth) using OSPF", draft- ietf-ospf-segment-routing-msd-05 (work in progress), June 2017. [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-10 (work in progress), October 2017. Tantsura, et al. Expires April 18, 2018 [Page 5] Internet-Draft Signaling MSD Using BGP-LS October 2017 [I-D.ietf-spring-segment-routing-mpls] Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing with MPLS data plane", draft-ietf-spring-segment-routing-mpls-10 (work in progress), June 2017. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [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, . 8.2. Informative References [I-D.ietf-isis-segment-routing-extensions] Previdi, S., Filsfils, C., Bashandy, A., Gredler, H., Litkowski, S., Decraene, B., and j. jefftant@gmail.com, "IS-IS Extensions for Segment Routing", draft-ietf-isis- segment-routing-extensions-13 (work in progress), June 2017. [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-19 (work in progress), August 2017. Authors' Addresses Jeff Tantsura Individual Email: jefftant.ietf@gmail.com Uma Chunduri Huawei Technologies Email: uma.chunduri@huawei.com Tantsura, et al. Expires April 18, 2018 [Page 6] Internet-Draft Signaling MSD Using BGP-LS October 2017 Greg Mirsky ZTE Corp. Email: gregimirsky@gmail.com Siva Sivabalan Cisco Email: msiva@cisco.com Tantsura, et al. Expires April 18, 2018 [Page 7]