Mirjam Kühne

Update on Assigning 32-bit ASNs

Mirjam Kühne
Contributors: Mike Petrusha
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The RIPE NCC has been assigning 32-bit Autonomous System Numbers since 2007. In this article we're providing an update about the number of 32-bit ASNs being assigned and how many are visible on the Internet.


As mentioned in Assigning 32-bit ASNs published one year ago, 16-bit Autonomous System Numbers (ASNs) are becoming a scarce resource just like 32-bit IP addresses. In 2007, the Internet Engineering Task Force (IETF) addressed this scarcity by developing a new format: 32-bit AS Numbers ( RFC 4893 ), which increased the supply of ASNs to four billion. The RIPE NCC started assigning 32-bit ASNs (or 4-byte ASNs as they are also called) in January 2007 by default. Upon request, however, the RIPE NCC still assigns 16-bit ASNs.

In Figure 1 below, you can see how the RIPE NCC has distributed 16-bit and 32-bit ASNs since 2007 (note: numbers for 2012 only include January-June).

16-bit and 32-bit ASNs Assigned in the RIPE NCC Service Region Figure 1: 16-bit (blue) compared to 32-bit (red) ASN assignments by the RIPE NCC

You can see that the percentage of 32-bit ASNs has been growing steadily since 2009.

In Figure 2, you can see that the RIPE NCC assigned 53% of all 32-bit ASNs. The number of 32-bit ASNs assigned by APNIC has gone up significantly since last year, however only a small percentage of these are visible in the global routing table (yet) - see Figure 3.

32-bit ASN Distribution by Region Figure 2: Global 32-bit ASN Distribution by RIR

Figure 3 shows the percentage of advertised 32-bit ASNs per region (thanks to Geoff Huston for providing this data). Of a total of 2,574 32-ASNs that are visible in the global routing table, 66% of them have been assigned by the RIPE NCC.

32-ASN BGP Visibility by Region Figure 3: Distribution of advertised 32-bit ASNs per region

Figure 4 shows advertised versus unadvertised 32-bit ASNs  the RIPE NCC service region only.

32-bit ASN Visiblity in the RIPE NCC Service Region Figure 4: Distribution of advertised vs. unadvertised 32-bit ASNs in the RIPE NCC service region

Out of 2,310 assigned 32-bit ASNs, 73% are visible in the global routing table. The remaining 620 are (not yet) visible. This is now comparable to 16-bit ASN visibility which is an improvement compared to last year's figures.

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

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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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