Applicability Statement for the Use of IPv6 UDP Datagrams with Zero Checksums
RFC 6936

Internet Engineering Task Force (IETF)                      G. Fairhurst
Request for Comments: 6936                        University of Aberdeen
Category: Standards Track                                  M. Westerlund
ISSN: 2070-1721                                                 Ericsson
                                                              April 2013

       Applicability Statement for the Use of IPv6 UDP Datagrams
                          with Zero Checksums

Abstract

   This document provides an applicability statement for the use of UDP
   transport checksums with IPv6.  It defines recommendations and
   requirements for the use of IPv6 UDP datagrams with a zero UDP
   checksum.  It describes the issues and design principles that need to
   be considered when UDP is used with IPv6 to support tunnel
   encapsulations, and it examines the role of the IPv6 UDP transport
   checksum.  The document also identifies issues and constraints for
   deployment on network paths that include middleboxes.  An appendix
   presents a summary of the trade-offs that were considered in
   evaluating the safety of the update to RFC 2460 that changes the use
   of the UDP checksum with IPv6.

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/rfc6936.

Fairhurst & Westerlund       Standards Track                    [Page 1]
RFC 6936      Applicability of Zero UDP Checksum with IPv6    April 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.

Fairhurst & Westerlund       Standards Track                    [Page 2]
RFC 6936      Applicability of Zero UDP Checksum with IPv6    April 2013

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Document Structure . . . . . . . . . . . . . . . . . . . .  5
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  5
     1.3.  Use of UDP Tunnels . . . . . . . . . . . . . . . . . . . .  6
       1.3.1.  Motivation for New Approaches  . . . . . . . . . . . .  6
       1.3.2.  Reducing Forwarding Costs  . . . . . . . . . . . . . .  6
       1.3.3.  Need to Inspect the Entire Packet  . . . . . . . . . .  7
       1.3.4.  Interactions with Middleboxes  . . . . . . . . . . . .  7
       1.3.5.  Support for Load Balancing . . . . . . . . . . . . . .  8
   2.  Standards-Track Transports . . . . . . . . . . . . . . . . . .  9
     2.1.  UDP with Standard Checksum . . . . . . . . . . . . . . . .  9
     2.2.  UDP-Lite . . . . . . . . . . . . . . . . . . . . . . . . .  9
       2.2.1.  Using UDP-Lite as a Tunnel Encapsulation . . . . . . . 10
     2.3.  General Tunnel Encapsulations  . . . . . . . . . . . . . . 10
     2.4.  Relationship of Zero UDP Checksum to UDP-Lite and UDP
           with Checksum  . . . . . . . . . . . . . . . . . . . . . . 11
   3.  Issues Requiring Consideration . . . . . . . . . . . . . . . . 12
     3.1.  Effect of Packet Modification in the Network . . . . . . . 13
       3.1.1.  Corruption of the Destination IP Address Field . . . . 14
       3.1.2.  Corruption of the Source IP Address Field  . . . . . . 15
       3.1.3.  Corruption of Port Information . . . . . . . . . . . . 16
       3.1.4.  Delivery to an Unexpected Port . . . . . . . . . . . . 16
       3.1.5.  Corruption of Fragmentation Information  . . . . . . . 18
     3.2.  Where Packet Corruption Occurs . . . . . . . . . . . . . . 20
     3.3.  Validating the Network Path  . . . . . . . . . . . . . . . 20
     3.4.  Applicability of the Zero UDP Checksum Method  . . . . . . 21
     3.5.  Impact on Non-Supporting Devices or Applications . . . . . 22
   4.  Constraints on Implementation of IPv6 Nodes Supporting