“.. and I’ve seen it before
.. and I’ll see it again
.. yes I’ve seen it before
.. just little bits of history repeating“
History Repeating, Propellerheads featuring Shirley Bassey
As the Internet began to grow rapidly in the early 1990s it became clear that the classful approach to routing, which had been introduced in 1981, would consume the IPv4 address space very fast and that improving the usage efficiency was needed. Classful Inter-Domain Routing, better known as CIDR, was introduced in 1993 and began to be deployed.
The introduction of a technology does not require its deployment, though and it took some years for classful routing to be phased out, with classful routing continuing beyond 2000. We are seeing a similar delay with another technical change today, Autonomous System Numbers (ASNs).
Internet Protocol (IP) addresses are mostly used as the unique identifiers for the devices we use to access the Internet, to provide services, and to support the network infrastructure. ASNs are the unique identifiers for Internet Service Providers’ (ISP) routing domains. If an IP address is equivalent to a street address, then an ASN is equivalent to a postal or zip code.
The Internet Engineering Task Force (IETF) expanded the pool of ASNs from a 16-bit space of 65,536 numbers to a 32-bit space of 4,294,967,296 numbers in 2007 in a way that enables compatibility between the use of 16-bit ASNs and 32-bit ANS. The “Global Policy for Allocation of ASN Blocks to Regional Internet Registries” (RIRs) was ratified the following year. It included a deployment timetable, at the end of which “IANA and the RIRs will cease to make any distinction” between the 16 and 32-bit ASNs.
In 2010 the policy was updated by the five regional addressing communities and ratified by the Board to push the deadline a year into the future. Two years ago I wrote a blog post noting there were only three blocks of 16-bit ASNs left. Today, they are almost gone and soon no-one will be able to get a fresh 16-bit ASN.
The number of ASNs in use grew by about 3,000 between the start of 2013 and 2014, and there are about that many unused 16-bit numbers left. The IANA Autonomous System Numbers registry now has fewer than 500 and the remainder is split between the five RIRs. Transit ISPs that want to be able to take on new multi-homed customers are going to have to turn on support for 32-bit ASNs very soon.
Here we are in 2014 and some new ISPs still experience problems with upstream providers not accepting their 32-bit ASNs. The technology is there but not everyone has deployed support for it, whether that’s in the routing infrastructure or operational support systems. It is time for all network providers to support 32-bit ASNs for the growth and health of the Internet.