Updated Specification of the IPv4 ID Field
RFC 6864

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Internet Engineering Task Force (IETF)                          J. Touch
Request for Comments: 6864                                       USC/ISI
Updates: 791, 1122, 2003                                   February 2013
Category: Standards Track
ISSN: 2070-1721

               Updated Specification of the IPv4 ID Field

Abstract

   The IPv4 Identification (ID) field enables fragmentation and
   reassembly and, as currently specified, is required to be unique
   within the maximum lifetime for all datagrams with a given source
   address/destination address/protocol tuple.  If enforced, this
   uniqueness requirement would limit all connections to 6.4 Mbps for
   typical datagram sizes.  Because individual connections commonly
   exceed this speed, it is clear that existing systems violate the
   current specification.  This document updates the specification of
   the IPv4 ID field in RFCs 791, 1122, and 2003 to more closely reflect
   current practice and to more closely match IPv6 so that the field's
   value is defined only when a datagram is actually fragmented.  It
   also discusses the impact of these changes on how datagrams are used.

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 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/rfc6864.

Touch                        Standards Track                    [Page 1]
RFC 6864           Updated Spec. of the IPv4 ID Field      February 2013

Copyright Notice

   Copyright (c) 2013 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
   2. Conventions Used in This Document ...............................3
   3. The IPv4 ID Field ...............................................4
      3.1. Uses of the IPv4 ID Field ..................................4
      3.2. Background on IPv4 ID Reassembly Issues ....................5
   4. Updates to the IPv4 ID Specification ............................6
      4.1. IPv4 ID Used Only for Fragmentation ........................7
      4.2. Encouraging Safe IPv4 ID Use ...............................8
      4.3. IPv4 ID Requirements That Persist ..........................8
   5. Impact of Proposed Changes ......................................9
      5.1. Impact on Legacy Internet Devices ..........................9
      5.2. Impact on Datagram Generation .............................10
      5.3. Impact on Middleboxes .....................................11
           5.3.1. Rewriting Middleboxes ..............................11
           5.3.2. Filtering Middleboxes ..............................12
      5.4. Impact on Header Compression ..............................12
      5.5. Impact of Network Reordering and Loss .....................13
           5.5.1. Atomic Datagrams Experiencing Reordering or Loss ...13
           5.5.2. Non-atomic Datagrams Experiencing
                  Reordering or Loss .................................14
   6. Updates to Existing Standards ..................................14
      6.1. Updates to RFC 791 ........................................14
      6.2. Updates to RFC 1122 .......................................15
      6.3. Updates to RFC 2003 .......................................16
   7. Security Considerations ........................................16
   8. References .....................................................17
      8.1. Normative References ......................................17
      8.2. Informative References ....................................17
   9. Acknowledgments ................................................19

Touch                        Standards Track                    [Page 2]
RFC 6864           Updated Spec. of the IPv4 ID Field      February 2013

1.  Introduction

   In IPv4, the Identification (ID) field is a 16-bit value that is
   unique for every datagram for a given source address, destination