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rfc:rfc2780

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].

Bradner & Paxson Best Current Practice [Page 1] RFC 2780 IANA Assignments March 2000

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.

Bradner & Paxson Best Current Practice [Page 2] RFC 2780 IANA Assignments March 2000

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

Bradner & Paxson Best Current Practice [Page 3] RFC 2780 IANA Assignments March 2000

 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.

Bradner & Paxson Best Current Practice [Page 4] RFC 2780 IANA Assignments March 2000

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

Bradner & Paxson Best Current Practice [Page 5] RFC 2780 IANA Assignments March 2000

 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.

Bradner & Paxson Best Current Practice [Page 6] RFC 2780 IANA Assignments March 2000

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.

Bradner & Paxson Best Current Practice [Page 7] RFC 2780 IANA Assignments March 2000

 [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.

Bradner & Paxson Best Current Practice [Page 8] RFC 2780 IANA Assignments March 2000

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

Bradner & Paxson Best Current Practice [Page 9] RFC 2780 IANA Assignments March 2000

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
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Bradner & Paxson Best Current Practice [Page 10]

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