Mirjam Kühne

Assigning 32-bit ASNs

Mirjam Kühne
Contributors: Alex Le Heux

The RIPE NCC has been assigning 32-bit Autonomous System Numbers for quite some time now. In this article we're showing a number of statistics and some analysis.

Note: Figure 2 in this article has been modified on 7 July 2012. Due to a typo, the number of 32-bit ASNs in the ARIN region was wrong.

With 16-bit Autonomous System Numbers (ASNs), 65,536 unique numbers are possible. Just like 32-bit IP addresses, these 16-bit ASNs are becoming a scarce resource. Therefore, in 2007 the Internet Engineering Task Force (IETF) developed a new format: 32-bit AS Numbers ( RFC 4893 ), which increases the supply of ASNs to four billion.

In January 2007 The RIPE NCC started assigning 32-bit ASNs (or 4-byte ASNs as they are also called) by default. Upon request, however, the RIPE NCC still assigns 16-bit ASNs.

In Figure 1 below, you can see the distribution of 32-bit ASNs compared to 16-bit ASNs the RIPE NCC assigned since 2007 (Please note that the numbers for 2011 only include January - July).

RIPE NCC ASN Distribution (16 vs. 32 bit)

Figure 1: 16-bit (blue) compared to 32-bit (red) ASN assignments by the RIPE NCC

In 2011, roughly one third of all ASNs assigned by the RIPE NCC consisted of 32 bits. This means that even with 32-bit ASNs available since 2007, quite a number of 16-bit ASNs are still being requested. However, as you can see in Figure 2, 65% of all 32-bit ASNs have been assigned by the RIPE NCC.

Global Distribution of 32-bit ASNs Figure 2: Global 32-bit ASN Distribution by RIR

If operators are using up-to-date equipment and software and their upstream provider supports 32-ASNs, they should not experience any problems. The RIPE NCC itself started using 32-bit ASNs in 2007 and has not experienced any problems.

However, as Figure 3 shows, 25% of all 32-bit ASNs assigned by the RIPE NCC, were returned. The main reason for this is that either the user or the upstream provider's equipment did not support 32-bit ASNs. This is becoming less of a problem as time goes by.

32-bit ASNs routed, not visible and returned Figure 3: Distribution of RIPE NCC assigned 32-bit ASNs returned, visible and not visible in BGP

Figure 3 shows that 52% of the 32-bit ASNs assigned by the RIPE NCC are visible in the global routing table, as compared to 23% that are not yet visible. When comparing this with 16-bit ASNs, we found that the visibility of 32-bit ASNs is lagging slightly behind. Overall, we can conclude that the majority of the RIPE NCC membership does not see any operational problems with 32-bit AS Numbers.


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About the author

Mirjam Kühne Based in Amsterdam, The Netherlands

I wrote the articles collected here during my time as community builder of the RIPE NCC and the maintainer and editor of RIPE Labs. I have since taken on a new role serving as the Chair of the RIPE Community. You can reach my new profile via the website link below.

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