Experimental Values In IPv4, IPv6, ICMPv4, ICMPv6, UDP, and TCP Headers
RFC 4727

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Network Working Group                                          B. Fenner
Request for Comments: 4727                          AT&T Labs - Research
Category: Standards Track                                  November 2006

                          Experimental Values
          in IPv4, IPv6, ICMPv4, ICMPv6, UDP, and TCP Headers

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2006).

Abstract

   When experimenting with or extending protocols, it is often necessary
   to use some sort of protocol number or constant in order to actually
   test or experiment with the new function, even when testing in a
   closed environment.  This document reserves some ranges of numbers
   for experimentation purposes in specific protocols where the need to
   support experimentation has been identified, and it describes the
   numbers that have already been reserved by other documents.

Fenner                      Standards Track                     [Page 1]
RFC 4727             Experimental Values in Headers        November 2006

1.  Introduction

   [RFC3692] recommends assigning option numbers for experiments and
   testing.  This document documents several such assignments for the
   number spaces whose IANA considerations are documented in [RFC2780].
   This document generally follows the form of [RFC2780].

   When using these values, carefully consider the advice in Sections 1
   and 1.1 of [RFC3692].  It is not appropriate to simply select one of
   these values and hard code it into a system.

   Note: while [RFC3692] says that it may not be necessary to allocate
   values for UDP and TCP ports, Sections 6 and 7.1 explicitly reserve
   ports for this purpose to avoid any possible conflict.

2.  Fields in the IPv4 Header

   The IPv4 header [RFC0791] contains the following fields that carry
   values assigned by the IANA: Version, Type of Service, Protocol,
   Source Address, Destination Address, and Option Type.

2.1.  IP Version Field in the IPv4 Header

   The Version field in IPv4 packets is always 4.

2.2.  IPv4 Type of Service Field

   [RFC2474] defines Pool 2 (all code points xxxx11, where 'x' refers to
   either '0' or '1') as Experimental/Local Use, so no additional code
   points should be needed.  The Explicit Congestion Notification (ECN)
   field [RFC3168] has no free code points to assign.

2.3.  IPv4 Protocol Field

   [RFC3692] allocates two experimental code points (253 and 254) for
   the IPv4 Protocol field.

2.4.  IPv4 Source and Destination Addresses

2.4.1.  IPv4 Unicast

   No experimental IPv4 addresses are defined.  For certain experiments,
   the address ranges set aside for Private Internets in [RFC1918] may
   be useful.  It is not appropriate to use other special-purpose IPv4
   addresses [RFC3330] for experimentation.

Fenner                      Standards Track                     [Page 2]
RFC 4727             Experimental Values in Headers        November 2006

   At the time of this writing, some Internet Registries have policies
   allowing experimental assignments from number spaces that they
   control.  Depending on the experiment, the registry, and their
   policy, this may be an appropriate path to pursue.

2.4.2.  IPv4 Multicast

   The globally routable group 224.0.1.20 is set aside for
   experimentation.  For certain experiments, the administratively
   scoped multicast groups defined in [RFC2365] may be useful.  This
   document assigns a single link-local scoped group, 224.0.0.254, and a
   single scope-relative group, 254.

2.5.  IPv4 Option Type Field

   This document assigns a single option number, with all defined values
   of the "copy" and "class" fields, resulting in four distinct option
   type codes.  See Section 8 for the assigned values.

3.  Fields in the IPv6 Header

   The IPv6 header [RFC2460] contains the following fields that carry
   values assigned from IANA-managed name spaces: Version, Traffic
   Class, Next Header, Source and Destination Address.  In addition, the
   IPv6 Hop-by-Hop Options and Destination Options extension headers
   include an Option Type field with values assigned from an IANA-
   managed name space.  The IPv6 Routing Header contains a Type field
   for which there is not currently an explicit IANA assignment policy.

3.1.  IP Version Field in the IPv6 Header

   The Version field in IPv6 packets is always 6.

3.2.  IPv6 Traffic Class Field

   [RFC2474] defines Pool 2 (all code points xxxx11, where 'x' refers to
   either '0' or '1') as Experimental/Local Use, so no additional code
   points should be needed.  The ECN field [RFC3168] has no free code