Why the current interest in IPv6? There are a lot of reasons, starting with the U.S. government's decision to convert to IPv6. The move is coming, and everyone on the Internet will be swept up in it - regardless of whether or not they've planned for it or are ready to make the change. But remember, this isn't new. IPv6 has been in the cards for many years. We've all ignored it quite happily so far. Why should we care now?
For years, the only reason for switching to IPv6 has been the desire to have more IP addresses. Meanwhile, clever people came up with Classless Inter-Domain Routing (CIDR) and Network Address Translation (NAT) boxes, both of which help us make more efficient use of existing IPv4 addresses.
So is the IPv4 address exhaustion finally upon us? Not quite yet. After all, 30.44% of all IPv4 addresses are still unassigned. Even the most daring forecasts don't see widespread use of IPv6 before 2011. But there are some good reasons to look at IPv6 now.
IPv6 Is Here
Are you planning on attending the Beijing Olympics? Your cab might be networked using IPv6. Even if you only plan on watching the games on television, the cameras recording the action might use IPv6. It is all part of the China Next-Generation Internet (CNGI) project. While some of their news is undoubtedly spin, there is also no doubt that China has good reasons to be looking at IPv6. China has a greater ratio of Internet users to available IPv4 addresses than almost any other country. This trend is likely to continue in the foreseeable future.
The U.S. government has set a much more modest goal: that the backbone networks of all federal agencies support IPv6 by June 30, 2008. The project appears to be on track, and so your 2008 taxes just might be processed using an IPv6-capable network.
IPv6 may not completely replace IPv4 for decades. On the other hand, it is clear that IPv6 is real today and that its market share is only likely to grow. IPv6 has been running on research networks for years now, so that means it is stable and well tested.
Connecting to IPv6
You don't need any special hardware to run IPv6 - unless you have high-end networking equipment. But just like any other networking protocol, running IPv6 does require two things: software and connectivity. Much of our software already supports IPv6. Windows and MacOS have fully supported IPv6 since 2003. Linux and the BSDs and other Unixes have also fully supported it since well before then.
The connectivity is a little harder to come by. For years, the action was on the "6bone" - a network carrying IPv6 traffic among IPv4-connected hosts. The 6bone was shut down once alternatives started to become available.
Until your ISP directly supports IPv6, the easiest way to connect to IPv6 hosts these days may be 6to4 (see the "Resources" links below this article). If you have one or more fixed IPv4 addresses, you can leverage them into IPv6 addresses (by prepending 2002: to the 32 bits of your IPv4 address), and set the default gateway to be a 6to4 router using the anycast address 126.96.36.199.
6to4 uses IP protocol number 41 when carrying IPv6 packets in IPv4 packets. Where NATs or firewalls would interfere with this, there is an alternative called Teredo, which uses UDP instead.
IPv6 and IPv4 Are Compatible
You don't have to give up IPv4 to use IPv6. In fact, as just discussed, there are ways to carry IPv6 traffic over IPv4-only networks.
Ideally, the two would be entirely interoperable and would be able to work transparently side by side. For example, a DNS query could be tried for the IPv6 AAAA record, and then the IPv4 record could be queried if the first query fails. The subsequent connection would then use IPv6 or IPv4 depending on which domain name resolution succeeds.
It seems likely that somebody will figure out that this is a good idea and make it happen at some point. However, that has not happened yet. So, for now, IPv4 and IPv6 interoperation are still clumsy.
Reports on IPv6-ready applications (including apache and a number of other servers, as well as simple clients such as wget)
Reports on the status of applications in Linux that are ready for IPv6, including everything from Mozilla and Firefox to Sendmail and Fetchmail