Segment Routing Path MTU in BGP
draft-li-idr-sr-policy-path-mtu-00

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Interdomain Routing Working Group                                  C. Li
Internet-Draft                                                     Z. Li
Intended status: Standards Track                     Huawei Technologies
Expires: January 3, 2019                                   July 02, 2018

                    Segment Routing Path MTU in BGP
                   draft-li-idr-sr-policy-path-mtu-00

Abstract

   Segment routing is a source routing paradigm that explicitly
   indicates the forwarding path for packets at the ingress node.  An SR
   policy is a set of candidate SR paths consisting of one or more
   segment lists with necessary path attributes.  However, the path
   maximum transmission unit (MTU) information for SR path is not
   available in the SR policy since the SR does not require signaling.
   This document defines extensions to BGP to distribute path MTU
   information within SR policies.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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 January 3, 2019.

Copyright Notice

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

Li & Li                  Expires January 3, 2019                [Page 1]
Internet-Draft             SR Path MTU in BGP                  July 2018

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  SR Policy for Path MTU  . . . . . . . . . . . . . . . . . . .   3
     3.1.  SR Path MTU Sub-TLV . . . . . . . . . . . . . . . . . . .   4
   4.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .   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

   Segment routing (SR) [I-D.ietf-spring-segment-routing] is a source
   routing paradigm that explicitly indicates the forwarding path for
   packets at the ingress node.  The ingress node steers packets into a
   specific path according to the Segment Routing Policy ( SR Policy) as
   defined in [I-D.ietf-spring-segment-routing-policy].  For
   distributing SR policies to the headend,
   [I-D.ietf-idr-segment-routing-te-policy] specifies a mechanism by
   using BGP, and new sub-TLVs are defined for SR Policies in BGP UPDATE
   message.

   The maximum transmission unit (MTU) is the largest size packet or
   frame, in bytes, that can be sent in a network.  An MTU that is too
   large might cause retransmissions.  Too small an MTU might cause the
   router to send and handle relatively more header overhead and
   acknowledgments.  When an LSP is created across a set of links with
   different MTU sizes, the ingress router needs to know what the
   smallest MTU is on the LSP path.  If this MTU is larger than the MTU
   of one of the intermediate links, traffic might be dropped, because
   MPLS packets cannot be fragmented.  Also, the ingress router may not
   be aware of this type of traffic loss, because the control plane for

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Internet-Draft             SR Path MTU in BGP                  July 2018
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