Twin hurdles that could trip internet upgrade plans

Two major shortages could hobble the internet's continued expansion, says internet infrastructure expert Daniel Karrenberg.

Everyone knows IPv4 addresses are running out. But less well known, and certainly less discussed, is the impending exhaustion of 16-bit, or two-byte, Autonomous System (AS) numbers. This numbering system is used to identify networks, rather than end-points. It is crucial to the operation of internet routing.

The internet is not going to shudder to a halt because of the exhaustion of 16-bit AS numbers or the shortage of IPv4 address space, but we should not play down the importance of these issues. The expansion of the internet relies on the availability of resources such as IP addresses and AS numbers.

The growing number of networks, end users and applications will all require addresses, and without widespread adoption of alternative numbering systems, exhaustion of either AS numbers or the IP address pool could seriously hamper this growth.

The AS-number and IP-address issues share some obvious similarities.

AS numbers and IP addresses identify specific parts of the internet: AS numbers can be seen as identifying ISPs, while IP addresses are used to identify the millions of end-systems on the internet, including end-users. The use and deployment of AS numbers is, however, restricted to the core of the network, while IP addresses are used throughout the internet.

The Internet Engineering Task Force, an international group responsible for producing protocol standards, best current practices and informational documents, has been aware of the impending exhaustion of IPv4 addresses and 16-bit AS numbers for some time, and has developed solutions to both problems.

In the case of IPv4, the solution is IPv6, a new protocol that expands addressing format to 128 bits, but which is not directly compatible with the old IPv4 protocol. Moving to 32-bit AS numbers will offer a similar answer to the 16-bit AS number problem, but 32-bit numbers will continue to be compatible in a network that uses 16-bit ones. Older technology, compatible only with 16-bit AS numbers, will need to be updated or replaced.

The combination of a smaller target audience and backward compatibility suggests that the transition to 32-bit AS numbers will require only a small amount of resources compared with the IPv6 transition.

Gradual introduction
Under a globally agreed policy, the five regional internet registries (RIRs) have been gradually introducing 32-bit AS numbers. Since 1 January, 2009, the RIRs have been assigning 32-bit AS numbers by default, but those who are not yet able to implement a 32-bit AS number in their network still have the option to request a 16-bit version.

However, from 1 January, 2010, the RIRs will no longer differentiate between the two varieties of AS number, meaning that from next year, you will not be able to avoid 32-bit AS numbers on the internet.

All these developments mean 32-bit AS numbers will be fully deployed well before the pool of available IPv4 addresses runs out. As a result, the introduction and deployment of 32-bit AS numbers may provide us with some insights into the ongoing deployment of IPv6.

I am following the uptake of 32-bit AS numbers with great interest. If the industry fails to clear this relatively easy hurdle, then the prospects for us making the much larger jump to IPv6 in a timely manner do not look good.

Daniel Karrenberg is chief scientist of the Ripe NCC, an independent not-for-profit organisation that supports the infrastructure of the internet for Europe, the Middle East and parts of central Asia and acts as the regional internet registry. He is a well-known figure in the global internet community and is the chairman of the Internet Society's board of trustees. Karrenberg was instrumental in establishing the global regional internet registry structure and is an active contributor to international discussions about internet governance.