[policy-wg] 4-Byte AS Number Policy Proposal

[Geoff Huston]

1. Author:  Geoff Huston

2. Organization: APNIC

3. Policy Affected: afpol-as200407-000 - ASN Allocation Policy

4. Date: 9 December 2005

Proposal:

4-Byte AS Number Policy Proposal

Author:
         Geoff Huston
         gih at apnic.net
         APNIC

Proposal Version:
         1.0

Proposal Type:
         New

Policy Term:
         Temporary (1 January 2007 ­ 1 January 2010)

Policy Statement:

         This policy proposal nominates 3 dates for changes to the
         current AS Number allocation policy for the registry:

         On 1 January 2007 the registry will process applications that
         specifically request 4-byte only AS Numbers and allocate such
         AS Numbers as requested by the applicant. In the absence of
         any specific request for a 4-byte only AS Number, a 2-byte
         only AS Number will be allocated by the registry.

         On 1 January 2009 the registry will process applications that
         specifically request 2-byte only AS Numbers and allocate such
         AS Numbers as requested by the applicant. In the absence of
         any specific request for a 2-byte only AS Number, a 4-byte
         only AS Number will be allocated by the registry.

         On 1 January 2010 the registry will cease to make any
         distinction between 2-byte only AS Numbers and 4-byte only AS
         Numbers, and will operate AS number allocations from an
         undifferentiated 4-byte AS Number allocation pool.

         Nomenclature

         It is proposed to identify 4-byte AS Numbers using a syntax of
         <high order 16 bit value in decimal>:<low order 16 bit value
         in decimal>. Accordingly, a 4-byte AS number of value 65546
         (decimal) would be identified as “1:10”.

         Terminology

         “2-byte only AS Numbers” refers to AS numbers in the range 0 ­
         65535

         “4-byte only AS Numbers” refers to AS Numbers in the range 1:0
         ­ 65535:65535 (decimal range 65,536 - 4,294,967,295)

         “4-byte AS Numbers” refers to AS Numbers in the range 0:0 ­
         65535:65535 (decimal range 0 ­ 4,294,967,295)

Rationale:

         Recent studies of AS number consumption rates indicate that
         the existing 2-byte pool of unallocated AS Numbers will be
         exhausted sometime in the period between 2010 and 2016, absent
         of any concerted efforts of recovery of already-allocated AS
         Numbers [1] [2]. Standardization work in the IETF has produced
         a document that is currently being submitted as a Proposed
         Standard that will expand the AS Number space to a 4-byte
         field [3].

         It is noted that some advance period may be required by
         network operators to undertake the appropriate procedures
         relating to support of 4-byte AS numbers, and while no flag
         day is required in the transition to the longer AS Number
         field, it is recognised that a prudent course of action is to
         allow for allocation of these extended AS numbers well in
         advance of an anticipated 2-byte AS Number exhaustion date.

         This policy proposal details a set of actions and associated
         dates for RIR AS Number allocation policies to assist in an
         orderly transition to use of the 4-byte AS Number space.

         The essential attributes of this policy proposal are to
         facilitate the ease of transitional arrangements by equipment
         vendors, network managers and network operations staff, to
         provide the industry with some predictability in terms of
         dates and associated actions with respect to registry
         operational procedures for AS Number allocations.

         References

         [1]  Daily AS Number Report,
              http://www.potaroo.net/tools/asns
         [2]  ASNs MIA: A Comparision of RIR Statistics and RIS
              Reality, http://www.nanog.org/mtg-0510/wilhelm.html
         [3]  BGP Support for Four-octet AS Number Space,
              draft-ietf-idr-as4bytes-12.txt

Timetable for implementation:

         Procedures to support this proposal need to be implemented
         by 1 January 2007