A selection of some of the biggest names on the web are readying themselves for World IPv6 Day, which begins tomorrow - and which could result in some issues for those with less forward-thinking ISPs.
World IPv6 day is a global test of the Internet's readiness to switch over to a new version of the Internet Protocol, from its current IPv4 standard - required, to put it simply, because we're running out of Internet.
When the IPv4 standard was created in 1980, it used a 32-bit addressing space - creating enough Internet for 4,294,967,296 unique machines. Back then, of course, only hardcore geeks, universities, and governments were connected - and that seemed an impossibly large figure to fill.
The creators of IPv4 were so confident that they would never need all that space, in fact, that they reserved large swathes of the address space for other uses - 18 million for privately-routed networks, and a further 270 million for multicast use.
Fast forward to 2011, however, and that 32-bit address space is getting mighty cramped. A huge number of homes are connected to the Internet, and your average person in the developed world is likely to have multiple Internet-connected devices: a PC, a laptop, a games console, a mobile phone - these all need to access the Internet.
Methods of cramming more systems into the IPv4 address space are used, such as Network Address Translation to allow multiple systems on a private network to share a single public-facing IP address - but they're not ideal, and even with such techniques the Internet is rapidly filling up.
IPv6 aims to address this problem by increasing the address space from its current 32-bit size to 128-bit, a massive increase with the number of addresses available doubling with each extra bit. A 33-bit address space, for example, offers 8,589,934,592 unique addresses - and the 128-bit address space in IPv6 offers a staggering 3.4×10³⁸ addresses.
IPv6, however, uses an entirely new addressing scheme - and isn't compatible with the existing IPv4 Internet. Sites that offer only IPv6 access won't be visible to IPv4 machines - and vice-versa.
To address this problem, the RFC document outlining IPv6 allows networks to run in a mixed-mode - accessing both IPv4 and IPv6 content. Websites are asked to offer both types of address to those who ask, allowing those ready for IPv6 to access the site via the new addressing system while maintaining compatibility with IPv4 systems.
It's a clever stop-gap, but one which is untested on a large scale - which is where World IPv6 Day comes in. Tomorrow, the likes of Google, Facebook, Yahoo!, and Akamai will switch on IPv6 access to their services for a 24 hour period - to see precisely what breaks.
Most users won't see any change to the services - but those running on ISPs with badly-configured servers, which have the potential to choke on IPv6-format addresses, could find their services interrupted. While that's an inconvenience, it's better to find out during a trial run than when the entire Internet goes over to IPv6 for real.
To help test out networks ahead of time, there's an on-line test that offers a wealth of technical detail about your system's readiness for IPv6 - along with a handy tick-box for whether World IPv6 Day is likely to cause you any problems.
For its paying Apps customers, Google is going a step further, offering a range of troubleshooting tips along with a form to report any issues accessing the company's services during the test - although if you find yourself disconnected on World IPv6 Day, you'll likely find it difficult to report the problem to Google on-line.
More information on World IPv6 Day is available over on the official website.