A Widely Deployed Solution to the Generic Routing Encapsulation (GRE) Fragmentation Problem
RFC 7588

Document Type RFC - Informational (July 2015; No errata)
Last updated 2015-10-14
Replaces draft-bonica-intarea-gre-mtu
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Internet Engineering Task Force (IETF)                         R. Bonica
Request for Comments: 7588                              Juniper Networks
Category: Informational                                     C. Pignataro
ISSN: 2070-1721                                            Cisco Systems
                                                                J. Touch
                                                                 USC/ISI
                                                               July 2015

 A Widely Deployed Solution to the Generic Routing Encapsulation (GRE)
                         Fragmentation Problem

Abstract

   This memo describes how many vendors have solved the Generic Routing
   Encapsulation (GRE) fragmentation problem.  The solution described
   herein is configurable.  It is widely deployed on the Internet in its
   default configuration.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7588.

Bonica, et al.                Informational                     [Page 1]
RFC 7588                    GRE Fragmentation                  July 2015

Copyright Notice

   Copyright (c) 2015 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
   (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
   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.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   5
   2.  Solutions . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  RFC 4459 Solutions  . . . . . . . . . . . . . . . . . . .   5
     2.2.  A Widely Deployed Solution  . . . . . . . . . . . . . . .   5
   3.  Implementation Details  . . . . . . . . . . . . . . . . . . .   6
     3.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  GRE MTU (GMTU) Estimation and Discovery . . . . . . . . .   6
     3.3.  GRE Ingress Node Procedures . . . . . . . . . . . . . . .   7
       3.3.1.  Procedures Affecting the GRE Payload  . . . . . . . .   7
       3.3.2.  Procedures Affecting the GRE Deliver Header . . . . .   8
     3.4.  GRE Egress Node Procedures  . . . . . . . . . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     5.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

Bonica, et al.                Informational                     [Page 2]
RFC 7588                    GRE Fragmentation                  July 2015

1.  Introduction

   Generic Routing Encapsulation (GRE) [RFC2784] [RFC2890] can be used
   to carry any network-layer protocol over any network-layer protocol.
   GRE has been implemented by many vendors and is widely deployed in
   the Internet.

   The GRE specification does not describe fragmentation procedures.
   Lacking guidance from the specification, vendors have developed
   implementation-specific fragmentation solutions.  A GRE tunnel will
   operate correctly only if its ingress and egress nodes support
   compatible fragmentation solutions.  [RFC4459] describes several
   fragmentation solutions and evaluates their relative merits.

   This memo reviews the fragmentation solutions presented in [RFC4459].
   It also describes how many vendors have solved the GRE fragmentation
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