Segment Routing Path MTU in BGP
draft-li-idr-sr-policy-path-mtu-03

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Interdomain Routing Working Group                                  C. Li
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                                  Y. Zhu
Expires: May 6, 2020                                       China Telecom
                                                                A. Sawaf
                                                   Saudi Telecom Company
                                                                   Z. Li
                                                     Huawei Technologies
                                                       November 03, 2019

                    Segment Routing Path MTU in BGP
                   draft-li-idr-sr-policy-path-mtu-03

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.

Status of This Memo

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Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Li, et al.                 Expires May 6, 2020                  [Page 1]
Internet-Draft             SR Path MTU in BGP              November 2019

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  SR Policy for Path MTU  . . . . . . . . . . . . . . . . . . .   3
     3.1.  SR Path MTU Sub-TLV . . . . . . . . . . . . . . . . . . .   4
   4.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   6
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   Segment routing (SR) [RFC8402] 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].  In order to distribute SR
   policies to the headend, [I-D.ietf-idr-segment-routing-te-policy]
   specifies a mechanism by using BGP.

   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
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