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Network Working Group                                         S. BradnerRequest for Comments: 2780                            Harvard UniversityBCP: 37                                                        V. PaxsonCategory: Best Current Practice                                    ACIRI                                                              March 2000IANA Allocation Guidelines For Values Inthe Internet Protocol and Related HeadersStatus 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 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   [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 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].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 inRFC 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 rangeBradner & 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.  SeeSection 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   inSection 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 20005.4.2 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 StandardsBradner & 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 20009.3 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,RFC792, September 1981.   [ICMPV6] Conta, A. and S. Deering, "Internet Control Message Protocol            (ICMPv6) for the Internet Protocol Version 6 (IPv6)",RFC2463, 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 200012. 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.orgBradner & Paxson         Best Current Practice                  [Page 9]

RFC 2780                    IANA Assignments                  March 200013. 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]