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32-bit AS Numbers: Operational Implications


Edited from an analysis by APNIC Chief Scientist, Geoff Huston.

If an ISP wants to use an AS number greater than 65535 (ie. A 32-bit AS number) then it will need to deploy a "new" version of the BGP protocol in its routers.

Since most existing BGP implementations use 16-bit data structures, introducing numbers in this expanded range means you need to deploy a version of BGP that "understands" 32-bit AS numbers.

But what about everyone else? What about the existing "old" BGP world that uses 16-bit AS numbers? Does everyone else have to upgrade their versions of BGP?

Even though every other network already has a 16-bit AS number, will every network also need to upgrade their BGP to see these new extended-length AS numbers? Will everyone need to apply some form of upgrade to their equipment and operational support systems (OSS) before the first extended length AS number is used in the public Internet?

The short answer is "No!" Current networks using 16-bit AS numbers need not change anything! However, there are some issues relating to the transition arrangements between 16- and 32-bit AS number routing which you may wish to address.

The transition approach was carefully constructed so that "new" 32-bit BGP implementations are backward compatible. So the reassuring news is that if you have a 16-bit AS number and are running 16-bit AS BGP today, then you do not need to change your routers.

The Internet will still work and you will continue to see routes to all advertised networks, irrespective of the existence of 32-bit AS numbers in the network. You will be able to send packets to those autonomous routing domains numbered from the 32-bit AS number space and they will be able to send packets back to you.

You don't need to upgrade your version of BGP, nor make any router configuration changes in your network. The Internet will work as intended without a break in connectivity.

However, some things might change for you. To understand what is going on, it is useful to describe how BGP has managed to be "backward compatible" across this change.

NEXT: Follow the link to find out more...Using AS 23456

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