Signaling Maximum SID Depth (MSD) Using OSPF
RFC 8476

Document Type RFC - Proposed Standard (December 2018; No errata)
Last updated 2018-12-12
Replaces draft-tantsura-ospf-segment-routing-msd
Stream IETF
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Stream WG state Submitted to IESG for Publication
Document shepherd Acee Lindem
Shepherd write-up Show (last changed 2018-05-21)
IESG IESG state RFC 8476 (Proposed Standard)
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Responsible AD Alvaro Retana
Send notices to Acee Lindem <acee@cisco.com>, aretana.ietf@gmail.com
IANA IANA review state Version Changed - Review Needed
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Internet Engineering Task Force (IETF)                       J. Tantsura
Request for Comments: 8476                                  Apstra, Inc.
Category: Standards Track                                    U. Chunduri
ISSN: 2070-1721                                      Huawei Technologies
                                                               S. Aldrin
                                                            Google, Inc.
                                                               P. Psenak
                                                           Cisco Systems
                                                           December 2018

              Signaling Maximum SID Depth (MSD) Using OSPF

Abstract

   This document defines a way for an Open Shortest Path First (OSPF)
   router to advertise multiple types of supported Maximum SID Depths
   (MSDs) at node and/or link granularity.  Such advertisements allow
   entities (e.g., centralized controllers) to determine whether a
   particular Segment Identifier (SID) stack can be supported in a given
   network.  This document only refers to the Signaling MSD as defined
   in RFC 8491, but it defines an encoding that can support other MSD
   types.  Here, the term "OSPF" means both OSPFv2 and OSPFv3.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8476.

Tantsura, et al.             Standards Track                    [Page 1]
RFC 8476                Signaling MSD Using OSPF           December 2018

Copyright Notice

   Copyright (c) 2018 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 ....................................................3
      1.1. Terminology ................................................4
      1.2. Requirements Language ......................................4
   2. Node MSD Advertisement ..........................................5
   3. Link MSD Sub-TLV ................................................6
   4. Procedures for Defining and Using Node and Link MSD
      Advertisements ..................................................7
   5. IANA Considerations .............................................7
   6. Security Considerations .........................................8
   7. References ......................................................9
      7.1. Normative References .......................................9
      7.2. Informative References ....................................10
   Acknowledgements ..................................................11
   Contributors ......................................................11
   Authors' Addresses ................................................11

Tantsura, et al.             Standards Track                    [Page 2]
RFC 8476                Signaling MSD Using OSPF           December 2018

1.  Introduction

   When Segment Routing (SR) paths are computed by a centralized
   controller, it is critical that the controller learn 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.

   [PCEP-EXT] defines how to signal MSD in the Path Computation Element
   Communication Protocol (PCEP).  However, if PCEP is not supported/
   configured on the head-end of an 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 (Distribution
   of Link-State and TE Information Using BGP) [RFC7752] defines a way
   to expose topology and associated attributes and capabilities of the
   nodes in that topology to a centralized controller.  MSD signaling by
   BGP-LS has been defined in [MSD-BGP].  Typically, BGP-LS is
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