Textual Representation of Autonomous System (AS) Numbers
Use decimal notation for all Autonomous System numbers.
Huston, G. and G. Michaelson, "Textual Representation of Autonomous System (AS) Numbers", RFC 5396, DOI 10.17487/RFC5396, December 2008, <https://www.rfc-editor.org/info/rfc5396>.
@misc{rfc5396,
series = {Request for Comments},
number = 5396,
howpublished = {RFC 5396},
publisher = {RFC Editor},
doi = {10.17487/RFC5396},
url = {https://www.rfc-editor.org/info/rfc5396},
author = {G. Huston and G. Michaelson},
title = {{Textual Representation of Autonomous System (AS) Numbers}},
pagetotal = 3,
year = 2008,
month = dec,
} RFC text
Contents
Network Working Group G. Huston
Request for Comments: 5396 G. Michaelson
Category: Standards Track APNIC
December 2008
Textual Representation of Autonomous System (AS) Numbers
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (c) 2008 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (http://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Abstract
A textual representation for Autonomous System (AS) numbers is
defined as the decimal value of the AS number. This textual
representation is to be used by all documents, systems, and user
interfaces referring to AS numbers.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Taxonomy of Representation Formats . . . . . . . . . . . . . . 2
3. Representation of AS Number Values . . . . . . . . . . . . . . 2
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 3
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 3
7. Informative References . . . . . . . . . . . . . . . . . . . . 3
1. Introduction
A textual representation for Autonomous System (AS) numbers is
defined as the decimal value of the AS number. This textual
representation is to be used by all documents, systems, and user
interfaces referring to AS numbers.
This document notes a number of potential representation formats and
proposes the adoption of a decimal value notation for AS numbers, or
"asplain" according to the representation taxonomy described here.
2. Taxonomy of Representation Formats
A taxonomy of representation for AS numbers is as follows:
asplain
refers to a syntax scheme of representing all AS numbers using
decimal integer notation. Using asplain notation, an AS number of
value 65526 would be represented as the string "65526" and an AS
number of value 65546 would be represented as the string "65546".
asdot+
refers to a syntax scheme of representing all AS numbers using a
notation of two integer values joined by a period character: <high
order 16-bit value in decimal>.<low order 16-bit value in
decimal>. Using asdot+ notation, an AS number of value 65526
would be represented as the string "0.65526" and an AS number of
value 65546 would be represented as the string "1.10".
asdot
refers to a syntax scheme of representing AS number values less
than 65536 using asplain notation and representing AS number
values equal to or greater than 65536 using asdot+ notation.
Using asdot notation, an AS number of value 65526 would be
represented as the string "65526" and an AS number of value 65546
would be represented as the string "1.10".
3. Representation of AS Number Values
To avoid confusion, a single textual notation is useful for
documentation, configuration systems, reports, and external tools and
information repositories. The decimal value representation, or
"asplain" is proposed as the textual notation to use for AS numbers.
The "asplain" representation represents the number as its decimal
value, without any field delimiter, corresponding to the lack of any
internal structure required by the use of AS numbers in the inter-
domain routing context.
4. IANA Considerations
IANA Registries should use decimal representation ("asplain") for AS
numbers.
5. Security Considerations
This document does not refer to matters associated with security of
routing systems.
6. Acknowledgments
The terminology of "asplain", "asdot", and "asdot+" was originally
devised and described by Juergen Kammer in January 2007 [KAMMER2007].
7. Informative References
[KAMMER2007] Kammer, J., "AS Number Formats", Jan 2007,
<http://quagga.ncc.eurodata.de/asnumformat.html>.
Authors' Addresses
Geoff Huston
Asia Pacific Network Information Centre
EMail: gih@apnic.net
George Michaelson
Asia Pacific Network Information Centre
EMail: ggm@apnic.net
AI ELI5
On this page
§1Why one format matters
Autonomous System numbers identify networks in inter-domain routing. For many years, the IANA and routing system have treated AS numbers as unstructured 32-bit integers. However, because 32-bit addresses felt limited before extended addressing, people began using a two-part notation similar to IP addresses. This led to multiple representation formats being used simultaneously in different systems, causing confusion when the same AS number might appear as 65526 in one system and 0.65526 in another.
Imagine if phone numbers could be written as 5551234567 or 555-123-4567 or 555-1234, all meaning the same thing. Everyone would get confused. One format is clearer.
§2The three formats
The asplain format represents all AS numbers using simple decimal notation, like 65546. The asdot+ format represents AS numbers using two 16-bit parts joined by a period, like 1.10, for use when the number exceeds 16-bit capacity. The asdot format used asplain for numbers less than 65536 but asdot+ for larger numbers. Only asplain avoids this inconsistency.
The three ways were: all-decimal (asplain), big-number-small-number (asdot+), or mix them (asdot). Asplain is simplest.
§3The standard: asplain
RFC 5396 designates asplain as the single textual representation for AS numbers in all documentation, configuration systems, reports, and tools. The asplain representation directly corresponds to the AS number's internal use in routing without any artificial structure. IANA registries must use decimal representation for AS numbers, making asplain the official standard.
From now on, write every AS number as plain decimals. That's the rule everyone agreed on.