Wherefore art thou, IPv6‾

IPv4 is less than 18 months away from hitting the wall, according to Vint Cerf, Google's chief internet evangelist and co-inventor of TCP/IP. Speaking to The Times in London last month, Cerf said that between the growing wave of mobile internet usage and the likely scramble by companies to secure whatever IPv4 addresses are left, the remaining 600 million IPv4 addresses will be used up by the end of 2009 or early 2010.

The depletion of IPv4 has been expected for years. The problem is that its replacement, IPv6 - which uses 128-bit IP addresses (compared to IPv4's 32-bit addresses) and can provide around four billion addresses per person - is barely out of the gate in terms of deployments.

Estimates vary as to how much IPv6 is deployed, but if you compare the number of IPv6 address blocks in the routing table with the number of autonomous systems (the rough equivalent of ISPs), AfriNIC (the regional internet registry for Africa and parts of the Indian Ocean) has the highest percentage of visible IPv6 prefixes at 22%, according to Leo Vegoda, manager of number resources at ICANN. IPv6 visibility for APNIC (which covers Asia Pacific) works out to 14% of ASs.

Those figures aren't equivalent to traffic usage, however. In August, Arbor Networks released the results of a study measuring a year's worth of IPv6 traffic from June 2007 through June 2008 on almost 2,400 backbone and peering routers across 87 ISPs worldwide. Results: inter-domain IPv6 traffic comprised 0.0026% of overall IPv4 traffic.

The Arbor study says that's probably a conservative figure, since it's only for IPv6 tunneled through IPv4, and doesn't include native IPv6, but the combined figure isn't likely to be much higher.

The holdup over IPv6 deployments is largely a business issue, as transitioning even to a dual-stack IPv4/IPv6 architecture is a costly and complex undertaking. That said, opinions differ as to how urgent the need for IPv6 is.

Black market addresses‾

The IETF has been looking at network address translation (NAT) solutions like NAT64 to help IPv4 and IPv6 interoperate and thus allow ISPs to migrate at their own pace, though critics say NAT is at best a stopgap and not a particularly elegant one. Meanwhile, an internet census report presented at last month's ACM Internet Measurement Conference claims that IPv4 has more mileage left in it than you think, as some companies are using a mere fraction of addresses they were allocated.

Even so, Cerf told the Times that he worries ISPs simply aren't taking the need for IPv6 seriously enough, and that once they realize they're out of IPv4 addresses, 'there is going to be a mad scramble for IPv6 and they won't implement it properly.'

How bad could it get‾ According to a panel session at the APNIC 26 conference in New Zealand in August, in which panelists worked through a hypothetical view of the state of the internet in 2015, a worst-case scenario could be the rise of a black market in IP address trading.

Johnny Martin, senior network engineer for FX Networks, who moderated the panel, said the scenario, while extreme, was 'not beyond the realms of possibility'.

'The foundation of the internet addressing policy to date has been one of open access based on need rather than ability to pay,' he said. 'Even in a legitimatized address trading environment, an open market could lead to a situation where the cost to obtain internet address space could become prohibitive for developing economies.'