Network Working Group S. Bradner
Request for Comments: 2780 Harvard University
BCP: 37 V. Paxson
Category: Best Current Practice ACIRI
March 2000
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 Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
This memo provides guidance for the IANA to use in assigning
parameters for fields in the IPv4, IPv6, ICMP, UDP and TCP protocol
headers.
1. Introduction
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
cases.
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].
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2. 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
[IPHC].
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.
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4.4 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].
4.4.1 IPv4 Unicast addresses
The Internet Corporation for Assigned Names and Numbers (ICANN)
recently accepted responsibility for the formulation of specific
guidelines for the allocation of the values from the IPv4 unicast
address space (values 0.0.0.0 through 223.255.255.255 ) other than
values from the ranges 0/8 (which was reserved in [AN80]) and 127/8
(from which the loopback address has been taken) along with other
values already assigned by the IETF for special functions or
purposes. (For example, the private addresses defined in RFC 1918.)
Further assignments in the 0/8 and 127/8 ranges require a Standards
Action process since current IP implementations may break if this is
done.
4.4.2 IPv4 Multicast addresses
IPv4 addresses that fall in the range from 224.0.0.0 through
239.255.255.255 are known as multicast addresses. The IETF through
its normal processes has assigned a number of IPv4 multicast
addresses for special purposes. For example, [ADSCP] assigned a
number of IPv4 multicast address to correspond to IPv6 scoped
multicast addresses. Also, the values in the range from 224.0.0.0 to
224.0.0.255 , inclusive, are reserved by the IANA for the use of
routing protocols and other low-level topology discovery or
maintenance protocols, such as gateway discovery and group membership
reporting. (See the IANA web page) New values in this range are
assigned following an IESG Approval or Standards Action process.
Assignments of individual multicast address follow an Expert Review,
IESG Approval or Standards Action process. Until further work is
done on multicast protocols, large-scale assignments of IPv4
multicast addresses is not recommended.
From time to time, there are requests for temporary assignment of
multicast space for experimental purposes. These will originate in
an IESG Approval process and should be for a limited duration such as
one year.
4.4.3 IPv4 Reserved addresses
IPv4 addresses in the range from 240.0.0.0 through 255.255.255.254
are reserved [AN81, MULT] and compliant IPv4 implementations will
discard any packets that make use of them. Addresses in this range
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are not to be assigned unless an IETF Standards Action modifies the
IPv4 protocol in such a way as to make these addresses valid.
Address 255.255.255.255 is the limited broadcast address.
4.5 IPv4 Option Type field
The IANA allocates values from the IPv4 Option Type name space
following an IESG Approval, IETF Consensus or Standards Action
process.
5. IANA Considerations for fields in the IPv6 header
The IPv6 header [V6] contains the following fields that carry values
assigned from IANA-managed name spaces: Version (by definition always
6 in IPv6), 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.
5.1 IPv6 Version field
The IPv6 Version field is always 6.
5.2 IPv6 Traffic Class field
The IPv6 Traffic Class field is described in [DIFF] as a 6- bit
Differentiated Services (DS) field and a 2-bit field which is
currently reserved. See Section 4.2 for assignment guidelines for
these fields.
5.3 IPv6 Next Header field
The IPv6 Next Header field carries values from the same name space as
the IPv4 Protocol name space. These values are allocated as discussed
in Section 4.3.
5.4 IPv6 Source and Destination Unicast Addresses
The IPv6 Source and Destination address fields both use the same
values and are described in [V6AD]. The addresses are divided into
ranges defined by a variable length Format Prefix (FP).
5.4.1 IPv6 Aggregatable Global Unicast Addresses
The IANA was given responsibility for all IPv6 address space by the
IAB in [V6AA]. Recently the IANA agreed to specific guidelines for
the assignment of values in the Aggregatable Global Unicast Addresses
FP (FP 001) formulated by the Regional Internet Registries.
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5.4.2 IPv6 Anycast Addresses
IPv6 anycast addresses are defined in [V6AD]. Anycast addresses are
allocated from the unicast address space and anycast addresses are
syntactically indistinguishable from unicast addresses. Assignment
of IPv6 Anycast subnet addresses follows the process described in
[V6AD]. Assignment of other IPv6 Anycast addresses follows the
process used for IPv6 Aggregatable Global Unicast Addresses.
(section 5.4.1)
5.4.3 IPv6 Multicast Addresses
IPv6 multicast addresses are defined in [V6AD]. They are identified
by a FP of 0xFF. Assignment guidelines for IPv6 multicast addresses
are described in [MASGN].
5.4.4 IPv6 Unassigned and Reserved IPv6 Format Prefixes
The responsibility for assigning values in each of the "unassigned"
and "reserved" Format Prefixes is delegated by IESG Approval or
Standards Action processes since the rules for processing these
Format Prefixes in IPv6 implementations have not been defined.
5.5 IPv6 Hop-by-Hop and Destination Option Fields
Values for the IPv6 Hop-by-Hop Options and Destination Options fields
are allocated using an IESG Approval, IETF Consensus or Standards
Action processes.
5.6 IPv6 Neighbor Discovery Fields
The IPv6 Neighbor Discovery header [NDV6] contains the following
fields that carry values assigned from IANA- managed name spaces:
Type, Code and Option Type.
Values for the IPv6 Neighbor Discovery Type, Code, and Option Type
fields are allocated using an IESG Approval or Standards Action
process.
6. IANA Considerations for fields in the IPv4 ICMP header
The IPv4 ICMP header [ICMP] contains the following fields that carry
values assigned from IANA-managed name spaces: Type and Code. Code
field values are defined relative to a specific Type value.
Values for the IPv4 ICMP Type fields are allocated using an IESG
Approval or Standards Action processes. Code Values for existing IPv4
ICMP Type fields are allocated using IESG Approval or Standards
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Action processes. The policy for assigning Code values for new IPv4
ICMP Types should be defined in the document defining the new Type
value.
7. IANA Considerations for fields in the IPv6 ICMP header
The IPv6 ICMP header [ICMPV6] contains the following fields that
carry values assigned from IANA-managed name spaces: Type and Code.
Code field values are defined relative to a specific Type value.
Values for the IPv6 ICMP Type fields are allocated using an IESG
Approval or Standards Action processes. Code Values for existing IPv6
ICMP Type fields are allocated using IESG Approval or Standards
Action processes. The policy for assigning Code values for new IPv6
ICMP Types should be defined in the document defining the new Type
value.
8. IANA Considerations for fields in the UDP header
The UDP header [UDP] contains the following fields that carry values
assigned from IANA-managed name spaces: Source and Destination Port.
Both the Source and Destination Port fields use the same namespace.
Values in this namespace are assigned following a Specification
Required, Expert Review, IESG Approval, IETF Consensus, or Standards
Action process. Note that some assignments may involve non-
disclosure information.
9. IANA Considerations for fields in the TCP header
The TCP header [TCP] contains the following fields that carry values
assigned from IANA-managed name spaces: Source and Destination Port,
Reserved Bits, and Option Kind.
9.1 TCP Source and Destination Port fields
Both the Source and Destination Port fields use the same namespace.
Values in this namespace are assigned following a Specification
Required, Expert Review, IESG Approval, IETF Consensus, or Standards
Action process. Note that some assignments may involve non-
disclosure information.
9.2 Reserved Bits in TCP Header
The reserved bits in the TCP header are assigned following a
Standards Action process.
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9.3 TCP Option Kind field
Values in the Option Kind field are assigned following an IESG
Approval or Standards Action process.
10. Security Considerations
Security analyzers such as firewalls and network intrusion detection
monitors often rely on unambiguous interpretations of the fields
described in this memo. As new values for the fields are assigned,
existing security analyzers that do not understand the new values may
fail, resulting in either loss of connectivity if the analyzer
declines to forward the unrecognized traffic, or loss of security if
it does forward the traffic and the new values are used as part of an
attack. This vulnerability argues for high visibility (which the
Standards Action and IETF Consensus processes ensure) for the
assignments whenever possible.
11. References
[ADSCP] Meyer, D., "Administratively Scoped IP Multicast", RFC 2365,
July 1998.
[AN80] Postel, J., "Assigned Numbers", RFC 758, August 1979.
[AN81] Postel, J., "Assigned Numbers", RFC 790, September 1981.
[CONS] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[DIFF] Nichols, K., Blake, S., Baker, F. and D. Black, "Definition
of the Differentiated Services Field (DS Field) in the IPv4
and IPv6 Headers", RFC 2474, December 1998.
[ECN] Ramakrishnan, K. and S. Floyd, "A Proposal to add Explicit
Congestion Notification (ECN) to IP", RFC 2481, January
1999.
[HC] Jacobson, V., "Compressing TCP/IP headers for low-speed
serial links", RFC 1144, February 1990.
[ICMP] Postel, J., "Internet Control Message Protocol", STD 5, RFC
792, September 1981.
[ICMPV6] Conta, A. and S. Deering, "Internet Control Message Protocol
(ICMPv6) for the Internet Protocol Version 6 (IPv6)", RFC
2463, December 1998.
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[IPHC] Degermark, M., Nordgren, S. and B. Pink, "IP Header
Compression", RFC 2507, February 1999.
[MASGN] Hinden, R. and S. Deering, "IPv6 Multicast Address
Assignments", RFC 2375, July 1998.
[MULT] Deering, S., "Host extensions for IP multicasting", RFC 988,
July 1986.
[NDV6] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998.
[TCP] Postel, J., "Transmission Control Protocol", STD 7, RFC 793,
September 1981.
[UDP] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August
1980.
[V4] Postel, J., "Internet Protocol", STD 5, RFC 791, September,
1981.
[V6] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[V6AA] IAB, IESG, "IPv6 Address Allocation Management", RFC 1881,
December 1995.
[V6AD] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
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12. Authors' Addresses
Scott Bradner
Harvard University
Cambridge MA - USA
02138
Phone: +1 617 495 3864
EMail: sob@harvard.edu
Vern Paxson
ACIRI / ICSI
1947 Center Street, Suite 600
Berkeley, CA - USA
94704-1198
Phone: +1 510 666 2882
EMail: vern@aciri.org
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13. Full Copyright Statement
Copyright (C) The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
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The limited permissions granted above are perpetual and will not be
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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