Transparent Interconnection of Lots of Links (TRILL): MTU Negotiation
RFC 8249

Document Type RFC - Proposed Standard (September 2017; No errata)
Last updated 2017-09-30
Replaces draft-zhang-trill-mtu-negotiation
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Internet Engineering Task Force (IETF)                          M. Zhang
Request for Comments: 8249                                      X. Zhang
Updates: 6325, 7177, 7780                                D. Eastlake 3rd
Category: Standards Track                                         Huawei
ISSN: 2070-1721                                               R. Perlman
                                                                Dell EMC
                                                           S. Chatterjee
                                                                   Cisco
                                                          September 2017

         Transparent Interconnection of Lots of Links (TRILL):
                            MTU Negotiation

Abstract

   The base IETF TRILL (Transparent Interconnection of Lots of Links)
   protocol has a TRILL campus-wide MTU feature, specified in RFCs 6325
   and 7177, that assures that link-state changes can be successfully
   flooded throughout the campus while being able to take advantage of a
   campus-wide capability to support jumbo packets.  This document
   specifies recommended updates to that MTU feature to take advantage,
   for appropriate link-local packets, of link-local MTUs that exceed
   the TRILL campus MTU.  In addition, it specifies an efficient
   algorithm for local MTU testing.  This document updates RFCs 6325,
   7177, and 7780.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8249.

Zhang, et al.                Standards Track                    [Page 1]
RFC 8249                     MTU Negotiation              September 2017

Copyright Notice

   Copyright (c) 2017 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
   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
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................3
      1.1. Conventions Used in This Document ..........................3
   2. Link-Wide TRILL MTU Size ........................................4
      2.1. Operations .................................................5
   3. Testing Link MTU Size ...........................................6
   4. Refreshing Sz ...................................................8
   5. Relationship between Port MTU, Lz, and Sz .......................9
   6. LSP Synchronization ............................................10
   7. Recommendations for Traffic Link Testing of MTU Size ...........10
   8. Backward Compatibility .........................................11
   9. Security Considerations ........................................11
   10. Additions to Configuration ....................................12
      10.1. Per-RBridge Configuration ................................12
      10.2. Per-RBridge Port Configuration ...........................12
   11. IANA Considerations ...........................................12
   12. References ....................................................12
      12.1. Normative References .....................................12
      12.2. Informative References ...................................14
   Acknowledgements ..................................................14
   Authors' Addresses ................................................14

Zhang, et al.                Standards Track                    [Page 2]
RFC 8249                     MTU Negotiation              September 2017

1.  Introduction

   [RFC6325] describes the way RBridges agree on the campus-wide minimum
   acceptable inter-RBridge MTU (Maximum Transmission Unit) size (called
   "Sz") to ensure that link-state flooding operates properly and all
   RBridges converge to the same link state.  For the proper operation
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