Network Working Group Scott Bradner
Internet-Draft Harvard University
Vern Paxson
ACIRI
January 2000
IANA Allocation Guidelines For Values In
the Internet Protocol and Related Headers
<draft-bradner-iana-allocation-04.txt>
Status of this Memo
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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.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
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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].
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.
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.
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4.2 IPv4 Type of Service field
The Type of Service field described in [V4] has been superceded
[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.
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 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
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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
255.255.255.255 are reserved [AN81, MULT] and compliant IPv4
implementations will discard any packets that make use of them.
Addresses in this range are not to be assigned unless an IETF
Standards Action modifies the IPv4 protocol in such a way as to
make these addresses valid.
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
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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 RFC 1881. 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.
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 used 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.
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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.
Values for the IPv4 ICMP Type and Code fields are allocated using an
IESG Approval or Standards Action processes.
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.
Values for the IPv6 ICMP Type and Code fields are allocated using an
IESG Approval or Standards Action processes.
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
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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.
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", RFC 2434, October 1998.
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[DIFF] Nichols, K., S. Blake, F. Baker, D. Black, "Definition of the
Differentiated Services Field (DS Field) in the IPv4 and IPv6
Headers", RFC 2474, December 1998.
[ECN] Ramakrishnan, K., S. Floyd, "A Proposal to add Explicit
Congestion Notification (ECN) to IP", RFC 2481, January 2000
[ICMP] Postel, J., "Internet Control Message Protocol", RFC 792,
September 1981.
[ICMPV6] Conta, A., S. Deering, "Internet Control Message Protocol
(ICMPv6) for the Internet Protocol Version 6 (IPv6)", RFC 2463,
December 1998.
[MASGN] Hinden, R., and S. Deering, "IPv6 Multicast Address
Assignments", RFC 2375, July 1998.
[MULT] Deering, S. E., "Host extensions for IP multicasting", RFC
988, July 1986
[NDV6] Narten, T., E. Nordmark, W. Simpson, "Neighbor Discovery for
IP Version 6 (IPv6)", RFC 2461, December 1998.
[TCP] Postel, J., "Transmission Control Protocol", RFC 793, September
1981.
[UDP] Postel, J., "User Datagram Protocol", RFC 768, August 1980.
[V4] Postel, J., "Internet Protocol", RFC 791, September, 1981.
[V6] Deering, S., R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.
[V6AD] Hinden, R., S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998
12. Author's Addresses
Scott Bradner
Harvard University
Cambridge MA - USA
02138
sob@harvard.edu
+1 617 495 3864
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Vern Paxson
ACIRI / ICSI
1947 Center Street, Suite 600
Berkeley, CA - USA
94704-1198
vern@aciri.org
+1 510/642-4274 x302
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