IKEv2 Fragmentation
draft-ietf-ipsecme-ikev2-fragmentation-08

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Document Type Active Internet-Draft (ipsecme WG)
Last updated 2014-05-23
Replaces draft-smyslov-ipsecme-ikev2-fragmentation
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Network Working Group                                         V. Smyslov
Internet-Draft                                                ELVIS-PLUS
Intended status: Standards Track                            May 23, 2014
Expires: November 24, 2014

                          IKEv2 Fragmentation
               draft-ietf-ipsecme-ikev2-fragmentation-08

Abstract

   This document describes the way to avoid IP fragmentation of large
   IKEv2 messages.  This allows IKEv2 messages to traverse network
   devices that do not allow IP fragments to pass through.

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
   Task Force (IETF).  Note that other groups may also distribute
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   This Internet-Draft will expire on November 24, 2014.

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   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Problem description  . . . . . . . . . . . . . . . . . . .  3
     1.2.  Proposed solution  . . . . . . . . . . . . . . . . . . . .  3
     1.3.  Conventions Used in This Document  . . . . . . . . . . . .  4
   2.  Protocol details . . . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.2.  Limitations  . . . . . . . . . . . . . . . . . . . . . . .  5
     2.3.  Negotiation  . . . . . . . . . . . . . . . . . . . . . . .  5
     2.4.  Using IKE Fragmentation  . . . . . . . . . . . . . . . . .  6
     2.5.  Fragmenting Message  . . . . . . . . . . . . . . . . . . .  7
       2.5.1.  Selecting Fragment Size  . . . . . . . . . . . . . . .  9
       2.5.2.  PMTU Discovery . . . . . . . . . . . . . . . . . . . . 10
       2.5.3.  Fragmenting Messages containing unprotected
               Payloads . . . . . . . . . . . . . . . . . . . . . . . 11
     2.6.  Receiving IKE Fragment Message . . . . . . . . . . . . . . 12
       2.6.1.  Replay Detection and Retransmissions . . . . . . . . . 14
   3.  Interaction with other IKE extensions  . . . . . . . . . . . . 15
   4.  Transport Considerations . . . . . . . . . . . . . . . . . . . 16
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 17
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 18
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 20
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 20
   Appendix A.  Design rationale  . . . . . . . . . . . . . . . . . . 22
   Appendix B.  Correlation between IP Datagram size and
                Encrypted Payload content size  . . . . . . . . . . . 23
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 25

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1.  Introduction

1.1.  Problem description

   The Internet Key Exchange Protocol version 2 (IKEv2), specified in
   [IKEv2], uses UDP as a transport for its messages.  Most IKEv2
   messages are relatively small, usually below several hundred bytes.
   Noticeable exception is IKE_AUTH Exchange, which requires fairly
   large messages, up to several kbytes, especially when certificates
   are transferred.  When IKE message size exceeds path MTU, it gets
   fragmented by IP level.  The problem is that some network devices,
   specifically some NAT boxes, do not allow IP fragments to pass
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