IKEv2 Fragmentation
draft-ietf-ipsecme-ikev2-fragmentation-03

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Network Working Group                                         V. Smyslov
Internet-Draft                                                ELVIS-PLUS
Intended status: Standards Track                         October 4, 2013
Expires: April 7, 2014

                          IKEv2 Fragmentation
               draft-ietf-ipsecme-ikev2-fragmentation-03

Abstract

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

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 7, 2014.

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   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Conventions Used in This Document  . . . . . . . . . . . .  3
   2.  Protocol details . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.2.  Limitations  . . . . . . . . . . . . . . . . . . . . . . .  4
     2.3.  Negotiation  . . . . . . . . . . . . . . . . . . . . . . .  4
     2.4.  Using IKE Fragmentation  . . . . . . . . . . . . . . . . .  5
     2.5.  Fragmenting Message  . . . . . . . . . . . . . . . . . . .  6
       2.5.1.  Selecting Fragment Size  . . . . . . . . . . . . . . .  7
       2.5.2.  Fragmenting Messages containing unencrypted
               Payloads . . . . . . . . . . . . . . . . . . . . . . .  8
     2.6.  Receiving IKE Fragment Message . . . . . . . . . . . . . .  9
       2.6.1.  Changes in Replay Protection Logic . . . . . . . . . . 10
   3.  Interaction with other IKE extensions  . . . . . . . . . . . . 12
   4.  Transport Considerations . . . . . . . . . . . . . . . . . . . 13
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 17
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 17
   Appendix A.  Design rationale  . . . . . . . . . . . . . . . . . . 18
   Appendix B.  Correlation between IP Datagram size and
                Encrypted Payload content size  . . . . . . . . . . . 19
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 20

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1.  Introduction

   The Internet Key Exchange Protocol version 2 (IKEv2), specified in
   [RFC5996], uses UDP as a transport for its messages.  When IKE
   message size exceeds path MTU, it gets fragmented by IP level.  The
   problem is that some network devices, specifically some NAT boxes,
   don't allow IP fragments to pass through.  This apparently blocks IKE
   communication and, therefore, prevents peers from establishing IPsec
   SA.

   The solution to the problem described in this document is to perform
   fragmentation of large messages by IKE itself, replacing them by
   series of smaller messages.  In this case the resulting IP Datagrams
   will be small enough so that no fragmentation on IP level will take
   place.

1.1.  Conventions Used in This Document
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