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).

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).

Figure 2: Global 32-bit ASN Distribution by RIR

Figure 3 shows advertised versus unadvertised 32-bit ASNs in the RIPE NCC service region only.

Figure 3: 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-ASNs, they should not experience any problems. The RIPE NCC itself started using 32-bit ASNs in 2007 and has not experienced any problems.

For more information and additional statistics, please see the background article on RIPE Labs.