Network Working Group S. Bradner
Request for Comments: 2780 Harvard University
BCP: 37 V. Paxson
Category: Best Current Practice ACIRI
IANA Allocation Guidelines For Values In
the Internet Protocol and Related Headers
Status of this Memo
This document specifies an Internet Best Current Practices for the
Internet Community, and requests discussion and suggestions for
improvements. Distribution of this memo is unlimited.
Copyright (C) The Internet Society (2000). All Rights Reserved.
This memo provides guidance for the IANA to use in assigning
parameters for fields in the IPv4, IPv6, ICMP, UDP and TCP protocol
For many years the Internet Assigned Numbers Authority (IANA)
(www.iana.org) has allocated parameter values for fields in protocols
which have been created or are maintained by the Internet Engineering
Task Force (IETF). Starting a few years ago the IETF began to
provide the IANA with guidance for the assignment of parameters for
fields in newly developed protocols. Unfortunately this type of
guidance was not consistently provided for the fields in protocols
developed before 1998. This memo attempts to codify existing IANA
practice used in the assignment of parameters in the specific case of
some of these protocols. It is expected that additional memos will
be developed in the future to codify existing practice in other
This memo addresses the fields within the IPv4, IPv6, ICMP, UDP and
TCP protocol headers for which the IANA assigns values.
The terms "Specification Required", "Expert Review", "IESG Approval",
"IETF Consensus", and "Standards Action", are used in this memo to
refer to the processes described in [CONS].
Bradner & Paxson Best Current Practice [Page 1]RFC 2780 IANA Assignments March 20002. Temporary Assignments
From time to time temporary assignments are made in the values for
fields in these headers for use in experiments. IESG Approval is
required for any such temporary assignments.
3. Version field in the IP header.
The first field in the IP header of all current versions of IP is the
Version field. New values in the Version field define new versions
of the IP protocol and are allocated only after an IETF Standards
Action. It should be noted that some of the Version number bits are
used by TCP/IP header compression schemes. Specifically, the hi-order
bit of the Version field is also used by TCP/IP header compression
[HC], while the three hi-order bits are used by IP Header Compression
4. IANA Considerations for fields in the IPv4 header
The IPv4 header [V4] contains the following fields that carry values
assigned by the IANA: Version, Type of Service, Protocol, Source
Address, Destination Address, and Option Type.
4.1 IPv4 IP Version field
The IPv4 Version field is always 4.
4.2 IPv4 Type of Service field
The Type of Service field described in [V4] has been superseded[DIFF]
by the 6-bit Differentiated Services (DS) field and a 2-bit field
which is currently reserved. The IANA allocates values in the DS
field following the IANA Considerations section in [DIFF]. [ECN]
describes an experimental use of the 2-bit "currently unused" field.
Other experimental uses of this field may be assigned after IESG
Approval processes. Permanent values in this field are allocated
following a Standards Action process.
4.3 IPv4 Protocol field
IANA allocates values from the IPv4 Protocol name space following an
Expert Review, IESG Approval or Standards Action process. The Expert
Review process should only be used in those special cases where non-
disclosure information is involved. In these cases the expert(s)
should be designated by the IESG.
Bradner & Paxson Best Current Practice [Page 2]RFC 2780 IANA Assignments March 20004.4 IPv4 Source and Destination addresses
The IPv4 source and destination addresses use the same namespace but
do not necessarily use the same values. Values in these fields fall
into a number of ranges defined in [V4] and [MULT].