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6rd Tunnel MTU
draft-foo-v6ops-6rdmtu-03

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Last updated: 2014-02-14
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Network Working Group                                    F. Templin, Ed.
Internet-Draft                              Boeing Research & Technology
Intended status: Informational                         February 14, 2014
Expires: August 18, 2014

                             6rd Tunnel MTU
                     draft-foo-v6ops-6rdmtu-03.txt

Abstract

   The tunnel MTU on 6rd Provider Edge (PE) and Consumer Edge (CE)
   routers is currently recommended to be set to 1480.  This is to avoid
   IPv4 fragmentation within the tunnel, but requires the tunnel ingress
   to drop any IPv6 packet larger than 1480 bytes and return an ICMPv6
   Packet Too Big (PTB) message.  Concerns for operational issues with
   both IPv4 and IPv6 Path MTU Discovery point to the possibility of
   MTU-related black holes when a packet is dropped due to an MTU
   restriction somewhere in the Internet.  Fortunately, the "Internet
   cell size" is 1500 bytes (i.e., the minimum MTU configured by the
   vast majority of links in the Internet) so if the 6rd PE router can
   set a tunnel MTU of at least 1500 bytes the MTU issues are
   alleviated.  This document specifies methods that can be employed to
   support these larger sizes.

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 August 18, 2014.

Copyright Notice

   Copyright (c) 2014 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

Templin                  Expires August 18, 2014                [Page 1]
Internet-Draft                    SEAL                     February 2014

   Provisions Relating to IETF Documents
   (http://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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   include Simplified BSD License text as described in Section 4.e of
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  6rd Provider Edge (PE) Router MTU Mitigations . . . . . . . . . 3
   3.  6rd Provider Edge (CE) Router MTU Mitigations . . . . . . . . . 4
   4.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 7

Templin                  Expires August 18, 2014                [Page 2]
Internet-Draft                    SEAL                     February 2014

1.  Introduction

   The tunnel MTU on 6rd Provider Edge (PE) and Consumer Edge (CE)
   routers is currently recommended to be set to 1500 bytes minus the
   IPv4 header encapsulation overhead minus the encapsulation overhead
   for any additional encapsulations that may occur on the path
   [RFC5969].  This is to avoid IPv4 fragmentation within the tunnel
   [RFC0791], but requires the tunnel ingress to drop any IPv6 packet
   larger than the tunnel MTU and return an ICMPv6 Packet Too Big (PTB)
   message [RFC2460].  Concerns for operational issues with both IPv4
   and IPv6 Path MTU Discovery [RFC1191][RFC1981] point to the
   possibility of MTU-related black holes when a packet is dropped due
   to an MTU restriction somewhere in the Internet.  Fortunately, the
   "Internet cell size" is 1500 bytes (i.e., the minimum MTU configured
   by the vast majority of links in the Internet) so if the 6rd PE
   router can set a tunnel MTU of at least 1500 bytes the MTU issues are

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