BIER MTU Discovery
draft-venaas-bier-mtud-02

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Last updated 2018-10-16
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Network Working Group                                          S. Venaas
Internet-Draft                                              IJ. Wijnands
Intended status: Experimental                                L. Ginsberg
Expires: April 19, 2019                              Cisco Systems, Inc.
                                                            M. Sivakumar
                                                        Juniper Networks
                                                        October 16, 2018

                           BIER MTU Discovery
                       draft-venaas-bier-mtud-02

Abstract

   This document defines an IGP based mechanism for discovering the MTU
   of a BIER sub-domain.  This document defines extensions to OSPF and
   IS-IS, but other protocols could potentially be extended.  MTU
   discovery is usually done for a given path, while this document
   defines it for a sub-domain.  This allows the computed MTU to be
   independent of the set of receivers.  Also, the MTU is independent of
   rerouting events within the sub-domain.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on April 19, 2019.

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
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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents

Venaas, et al.           Expires April 19, 2019                 [Page 1]
Internet-Draft             BIER MTU Discovery               October 2018

   carefully, as they describe your rights and restrictions with respect
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
   3.  MTU discovery procedure . . . . . . . . . . . . . . . . . . .   3
   4.  IS-IS BIER Sub-Domain MTU Sub-sub-TLV . . . . . . . . . . . .   4
   5.  OSPF BIER Sub-Domain MTU Sub-TLV  . . . . . . . . . . . . . .   5
   6.  IANA considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   This document defines an IGP based mechanism for discovering the MTU
   of a BIER sub-domain.  The discovered MTU indicates the largest
   possible BIER packet that can be sent across any link in a BIER sub-
   domain.  This is different from [I-D.ietf-bier-path-mtu-discovery]
   which performs Path MTU Discovery (PMTUD) for a set of receivers.
   PMTUD is based on probing, and when there are routing changes, e.g.,
   a link going down, the actual MTU for a path may become less than was
   previously discovered, and there will be some delay until the next
   probe is performed.  Also, the set of receivers for a flow may change
   at any time, which may cause the MTU to change.  This document
   instead discovers a BIER sub-domain MTU, which is independent of
   paths and receivers within the sub-domain.

   Discovering the sub-domain MTU is much simpler than discovering the
   multicast path MTU, and is more robust with regards to path changes
   as discussed above.  However, the sub-domain MTU may be a lot smaller
   than the path MTU would have been for a given flow.  The discovery
   mechanisms may be combined, allowing the discovery of the path MTU
   for certain flows as needed.

   The BIER sub-domain MTU defined here provides the maximum size of a
   BIER packet that can be forwarded through the sub-domain regardless
   of path.  A BIER router that performs BIER encapsulation will need to
   subtract the encapsulation overhead to find the largest size packet
   that can be encapsulated.  This would give the IP MTU, and may be
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