ARIN Switching to ASPLAIN Notation, 13 March 2009

Posted: Tue, 10 Mar 2009

With the publication of RFC 5396, the IETF standardized the representation of all Autonomous System (AS) Numbers in the ASPLAIN format.  In order to comply with this new standard, ARIN will be deprecating AS-DOT notation for 4-byte AS numbers in favor of ASPLAIN notation on March 13, 2009, at approximately 10:00PM EDT.  This event will not interrupt any ARIN-provided services, and the only noticeable change will be to the display of 4-byte AS numbers in ARIN WHOIS.

Please note that ARIN WHOIS will continue to accept queries in both ASPLAIN and AS-DOT notation.

You can view RFC 5396 at:

If you have any questions or concerns, please do not hesitate to contact


Mark Kosters
Chief Technical Officer
American Registry for Internet Numbers (ARIN)