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Network Working Group                                      G. Michaelson
Internet-Draft                                                     APNIC
Intended status: Informational                          October 15, 2006
Expires: April 18, 2007


         Canonical Textual Representation of 4-byte AS Numbers
              draft-michaelson-4byte-as-representation-02

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Copyright Notice

   Copyright (C) The Internet Society (2006).














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Internet-Draft    Canonical Textual Form of 4-byte ASN      October 2006


Abstract

   A single textual representation for 4-byte Autonomous System (AS)
   numbers is defined, to avoid any confusion in interpreting the two
   2-byte quantities of which it is comprised.  The syntax chosen avoids
   collision with Border Gateway Protocol (BGP) community string parsing
   of AS numbers.  It is recommended that only this textual
   representation be used by all documents and systems referring to
   4-byte AS numbers.










































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Internet-Draft    Canonical Textual Form of 4-byte ASN      October 2006


1.  Nomenclature

   4 Byte AS numbers are defined in [IDR4BYTES]

   4-byte AS numbers are represented 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
   represented as the string "1.10".








































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Internet-Draft    Canonical Textual Form of 4-byte ASN      October 2006


2.  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)










































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3.  Discussion

   To avoid confusion, a single textual notation to represent a 4-byte
   AS number is defined.  This is for use in documentation,
   configuration systems, and external tools and information
   repositories.

   2-byte only AS numbers MAY be represented as a 16 bit value decimal
   number, with no leading zeros, or ".".  They may also be represented
   as 4-byte AS numbers.

   4-byte AS numbers MAY be represented identically as 2-byte only AS
   numbers, if their value lies in the range 0 - 65535.  Otherwise, they
   MUST be represented identically as for 4-byte only AS numbers.  For
   values in the range 0 - 65535 the canonical 4-byte AS number
   representation is 0. < 16 bit decimal value > .

   all other 4-byte AS numbers take a non-zero value in the high order
   16 bit decimal value.

   4-byte only AS numbers MUST be represented as two pairs of 16-bit
   decimal values with no leading zeros, separated by the "." character.
   The first decimal value is the high-order 16 bits, the second decimal
   value is the low order 16 bits.

   During the transitional period, when not all systems understand 4
   byte AS numbers, it may be neccessary to continue to use two
   notations to represent the 16-bit values which represent the AS
   numbers 0 - 65535.  These 2 byte AS numbers need a canonical textual
   representation in 4-byte AS number representation.

   Once all systems are converted to using 4-byte AS numbers, only 4
   byte AS number representation should be used.


















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4.  Historical Approaches

   Initially, the ":" was proposed to separate the 2-byte components.
   However this clashes with use of the ":" character in community
   attribute syntax in BGP and this would have required changes to the
   routing systems code base in ways which are not acceptable.

   Routing Protocol Specification Language (RPSL) [RFC2622] [RFC4012]
   AS-Set objects use the ":" character to denote sequences of AS
   objects forming a chain.  Since the AS object would have had the ":"
   character embedded in the instance name, this would have required
   double-parsing to find 4-byte AS number in AS-Set chains.  This also
   is not acceptable.

   The "." denoted representation does not present these problems.

   This notation has been informally adopted by at least one vendor, and
   used consistently in presentations in the Regional Internet Registry
   (RIR) community towards the deployment of 4-byte AS numbers.
   Therefore it seems sensible to formalize its use as the preferred
   representation of a 4-byte AS numbers across the board.






























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5.  IANA Considerations

   This document recommends changes to an existing IANA Registry, the as
   number assignments registry.

   This document makes changes to the IANA Considerations text in
   [IDR4BYTES] as follows:

   It is recommended that upon approval of this document, the IANA will
   change the rules for representation of the assignments in the
   "AUTONOMOUS SYSTEM NUMBERS" registry located at
   http://www.iana.org/assignments/as-numbers

   New line in the registry will be:

   1.0 - 65535.65535 Reserved by the IANA

   maintained subsequently in the documented textual representation as
   assignments are made to the RIR.
































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Internet-Draft    Canonical Textual Form of 4-byte ASN      October 2006


6.  Acknowledgements

   This proposal was motivated by a discussion with Geoff Huston.  The
   text of the definition of a 4-byte AS is taken from [RIPE2005-12]

   The author thanks Rudiger Volk, Joao Damas, Joe Abley, Peter Koch and
   Henk Uijterwaal for feedback and extensive comments on this draft.












































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7.  Implementation Notes

   Many programming languages treat xxx.yyy numeric strings as real
   number values on input, and convert internally to a canonical
   floating point representation.  Since the precision cannot be
   guaranteed to be preserved, this risks changing the value of the 32-
   bit quantity on output, or by mis-placed arithmetical calculation.

   Care must be taken that 4-byte AS numbers are treated as 'special-
   purpose strings' on input and output, and parsed correctly to a 32
   bit quantity.  It would be sensible to draft suitable function
   definitions to define the transform from presentation to internal
   value, as was done for IPv4 and IPv6 addresses with the inet_pton()
   and inet_ntop() functions.

   The [RFC2622] and [RFC4012] specifications, and systems which
   manipulate AS numbers need to be reviewed for conformance with 4-byte
   AS number textual representation, and for the syntactic implications
   of this representation.
































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8.  Changes since the -01 draft

   An IANA Considerations section has been added to amend an existing
   registry.

   The document now clarifies that it refers to a textual
   representation, the binary representation used on-the-wire is
   unaffected by this draft.











































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Internet-Draft    Canonical Textual Form of 4-byte ASN      October 2006


9.  Informative References

   [IDR4BYTES]
              Vohra, Q. and E. Chen, "draft-ietf-idr-as4bytes-12",
              Dec 2005, <http://www1.ietf.org/internet-drafts/
              draft-ietf-idr-as4bytes-12.txt>.

   [RFC2622]  Alaettinoglu, C., Villamizar, C., Gerich, E., Kessens, D.,
              Meyer, D., Bates, T., Karrenberg, D., and M. Terpstra,
              "Routing Policy Specification Language (RPSL)", RFC 2622,
              June 1999.

   [RFC4012]  Blunk, L., Damas, J., Parent, F., and A. Robachevsky,
              "Routing Policy Specification Language next generation
              (RPSLng)", RFC 4012, March 2005.

   [RIPE2005-12]
              Huston, G., "4-Byte AS Number Policy", Dec 2005, <
              http://www.ripe.net/ripe/policies/proposals/2005-12.html>.
































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Author's Address

   George Michaelson
   Asia Pacific Network Information Centre
   Level 1, 33 Park Road
   Milton, Queensland  4064
   AU

   Phone: +61 7 3858 3100
   Email: ggm@apnic.net









































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