32-bit AS numbers are here (posted 2006-12-29)

If you want to use the BGP routing protocol, you need an Autonomous System number. These AS numbers were 16 bits in size until now, allowing for around 64000 ASes, and more than half of those have been given out already. To avoid problems when we run out of AS numbers, the IETF came up with modifications to BGP to allow for 32-bit AS numbers, as I explained in a posting about a year ago.

Obviously, at some point someone has to bite the bullet and start using one of these new AS numbers. This bullet biting may happen fairly soon, as the five Regional Internet Registries have all adopted, or are in the process of adopting, the following policy:

• As of january first, 2007, it will be possible to request a 32-bit AS number.
• As of january first, 2009, the RIRs will be giving out 32-bit AS numbers to everyone who requests an AS number and doesn't specifically ask for a 16-bit compatible one.
• And as of january first, 2010, there will cease to be a difference between 16-bit and 32-bit AS numbers and the transition will be complete.

So what does this mean for people who run BGP today? Not all that much, really, because the changes to BGP to support the longer AS numbers are completely backward compatible. The only change is that you'll see the AS number 23456 appear in more and more places. In routers that don't yet support 32-bit ASes, the special 16-bit AS number 23456 shows up as a placeholder in places where a 32-bit AS is supposed to appear.

If you have scripts that perform AS-related operations on the Routing Registries (such as the RIPE database), you'll have to adjust your software to parse the new format for 32-bit AS numbers. They are written down as <16bits>.<16bits>, for instance, 3.1099 is a new 32-bit AS number and 0.23456 is the 32-bit version of AS 23456. However, this format isn't standardized so 32-bit AS numbers may show up differently in your router. Have a look at the RIPE announcement.

As soon as the first 32-bit AS number appears in the wild I'll report it here so you can check whether it shows up in its full 32-bit glory or as 23456. In the mean time, you may want to ask your router vendor for 32-bit AS support. At least one of the big vendors isn't implementing it in all of their lines just yet because they claim there is no customer demand for it.