Signaling MSD (Maximum SID Depth) using OSPF
draft-ietf-ospf-segment-routing-msd-20

Document Type Active Internet-Draft (lsr WG)
Last updated 2018-09-17 (latest revision 2018-08-31)
Replaces draft-tantsura-ospf-segment-routing-msd
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Telechat date On agenda of 2018-09-27 IESG telechat
Needs 8 more YES or NO OBJECTION positions to pass.
Responsible AD Alvaro Retana
Send notices to Acee Lindem <acee@cisco.com>, aretana.ietf@gmail.com
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OSPF Working Group                                           J. Tantsura
Internet-Draft                                            Nuage Networks
Intended status: Standards Track                             U. Chunduri
Expires: March 4, 2019                               Huawei Technologies
                                                               S. Aldrin
                                                             Google, Inc
                                                               P. Psenak
                                                           Cisco Systems
                                                         August 31, 2018

              Signaling MSD (Maximum SID Depth) using OSPF
                 draft-ietf-ospf-segment-routing-msd-20

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 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.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on March 4, 2019.

Copyright Notice

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

Tantsura, et al.          Expires March 4, 2019                 [Page 1]
Internet-Draft                                               August 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.  Using Node and Link MSD Advertisements  . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   7
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

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

   Path Computation Element Protocol(PCEP) SR draft
   [I-D.ietf-pce-segment-routing] signals MSD in SR Path Computation
   Element Capability TLV and METRIC Object.  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
   [I-D.ietf-idr-bgp-ls-segment-routing-msd].  Typically, BGP-LS is
   configured on a small number of nodes that do not necessarily act as
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