OVUM評論：IPv4 Address Shortage Approaching

2011 to see IPv4 address rationing

The last two /8 blocks (of approximately 16m IPv4 addresses each) to be allocated according to demand and normal processes has just been made by IANA to APNIC. IANA, the Internet Assigned Numbers Authority, will now allocate one each of the last remaining five /8 blocks to each of the Regional Internet Registries (RIRs). The RIRs make further delegations of smaller address blocks to ISPs and other organisations within their respective regions.

APNIC (the RIR for Asia Pacific) will switch to a rationing policy once they reach their final /8 worth of unallocated addresses to maximise the period that small allocations of IPv4 addresses are available for new networks. Under this policy, each APNIC account holder can receive only one minimum size block (a /22 which consists of only 1024 IPv4 addresses). It is expected that this policy will come into effect mid to late 2011.

Despite the plentiful predictions and warnings for some time that this point was approaching, some organisations will undoubtedly be caught by surprise. IPv6 addresses were designed as the solution to the predicted shortage of IPv4 addresses, but as an industry, it has been easier to extend usage of IPv4 rather than undergo the challenge of transitioning to IPv6.

IPv6 versus IPv4

The obvious advantage of IPv6 to IPv4 is the substantially expanded address range. Every one of the current world population of 6.9b people could be assigned an address range 19 orders of magnitude greater than the entire IPv4 address range. Even with an explosion of machine-to-machine communications and assigning globally unique addresses to real world objects, this should suffice until we are well into deploying an interstellar internet.

The inevitable exhaustion of the IPv4 address range has been heroically delayed with DHCP and Network Address Translators (NATs) that allow sharing of public IP addresses amongst a pool of users. Unfortunately NATs break the end-to-end communications principle of the internet, causing many complications for developers, particularly of services such as VoIP, video conferencing and P2P. Aside from removing the NAT complexity, IPv6 also allows for simplified network configuration with provision for automatic address assignment and network renumbering.

For mobile devices, IPv6 allows the possibility to provide globally unique addresses. With mobile IP, these devices can move between networks while maintaining the same IPv6 address. IPSec is built into IPv6, so all IPv6 devices will support network layer authentication and encryption. Likewise for multicasting, being built into IPv6 rather than optional as for IPv4 means that multicasting of video in IPv6 networks will be universally supported, allowing more efficient support of increasingly popular video services.

Despite first being deployed in 1999, the reason IPv6 is not ubiquitous today is that it is not backwards compatible with IPv4. This makes the transition difficult and it will therefore be necessary to simultaneously maintain IPv4 and IPv6 for many years and to provide solutions for interworking during the transition period.