Where can I find out more about 32-bit ASNs?

The following Internet Engineering Task Force (IETF) documents offer more information about 32-bit ASNs:

BGP Support for Four-octet AS Number Space (RFC 4893)
This document describes the changes to the BGP protocol and the 16-bit ASN to 32-bit ASN transition mechanism.

A list of operating system versions compatible with 32-bit ASNs is available at:
http://as4.cluepon.net/index.php/Software_Support