32-bit Autonomous System Numbers: A Guide for LIRs
1 January 2009 - The RIPE NCC began assigning 32-bit (or four-byte) Autonomous System Numbers (ASNs) by default. This is in accordance with a common policy agreed on in all Regional Internet Registry (RIR) communities and described in the RIPE Document, Autonomous System (AS) Number Assignment Policies and Procedures.
16-bit ASNs and 32-bit ASNs are interoperable. Those who have previously received a 16-bit ASN will not need to renumber. It is possible some devices, either in your network or the network of your upstream provider, will not be compatible with 32-bit ASNs. It is therefore vital network operators be aware of the new assignment policy and of their own network's status in terms of 32-bit ASN compatibility.
Even if you do not plan to expand your network, you should still check your tools continue to work when you enter a 32-bit ASN.
Requesting an AS Number from the RIPE NCC
When requesting an ASN after 1 January, LIR staff should ensure that 32-bit ASNs will be compatible with their existing networks. Some network operators may experience difficulties configuring BGP sessions if their or their upstream providers' equipment is not compliant with the new 32-bit standard.
When using the revised LIR Portal ASN request form, you will see it is still possible to select a 16-bit ASN. While the 32-bit option is initially selected by default, you can select a 16-bit ASN option.
If you wish to select this option, you are asked to provide some information on why a 32-bit ASN will not be compatible with your network. This assists the RIPE NCC when evaluating the deployment of 32-bit ASNs and identifying any issues needing further attention.
The RIPE website has a 32-bit ASN FAQ page, containing a range of information about 32-bit ASNs and associated RIPE community policies and RIPE NCC procedures.
To help vendors understand how to provide 32-bit ASN support and to help network operators find products supporting 32-bit ASNs, APNIC has set up a special website called Introduction to Four-byte AS Numbers