Signaling MSD (Maximum SID Depth) using OSPF
draft-ietf-ospf-segment-routing-msd-25

Document Type Active Internet-Draft (lsr WG)
Last updated 2018-11-15 (latest revision 2018-10-18)
Replaces draft-tantsura-ospf-segment-routing-msd
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OSPF Working Group                                           J. Tantsura
Internet-Draft                                              Apstra, Inc.
Intended status: Standards Track                             U. Chunduri
Expires: April 20, 2019                              Huawei Technologies
                                                               S. Aldrin
                                                             Google, Inc
                                                               P. Psenak
                                                           Cisco Systems
                                                        October 17, 2018

              Signaling MSD (Maximum SID Depth) using OSPF
                 draft-ietf-ospf-segment-routing-msd-25

Abstract

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

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on April 20, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Tantsura, et al.         Expires April 20, 2019                 [Page 1]
Internet-Draft                                              October 2018

   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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  Node MSD Advertisement  . . . . . . . . . . . . . . . . . . .   4
   3.  Link MSD sub-TLV  . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Procedures for Defining and Using Node and Link MSD
       Advertisements  . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   8
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   When Segment Routing (SR) paths are computed by a centralized
   controller, it is critical that the controller learns the Maximum SID
   (Segment Identifier) Depth (MSD) that can be imposed at each node/
   link on a given SR path to ensure that the Segment Identifier (SID)
   stack depth of a computed path doesn't exceed the number of SIDs the
   node is capable of imposing.

   [I-D.ietf-pce-segment-routing] 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 controller does not participate in IGP
   routing, it has no way to learn the MSD of nodes and links.  BGP-LS
   (Distribution of Link-State and TE Information using Border Gateway
   Protocol) [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
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