We're sorry. The IPv4 address you are trying to reach has been disconnected.

The problem with the IPv6 migration isn't technical, but social. IPv4 was the version of the protocol that was active when the Internet "went pop", and as such, many people (especially those who actually pay for the technology, rather than actually use it directly) think it is good enough. It doesn't help matters that workarounds and kludges like NAT are regarded nowadays as features instead of flaws.

Arguably, there's an element of discrimination here too. Large American and European corporations and governments have plenty of IP addresses. (For a start, have a look at: http://en.wikipedia.org/wiki/List_of_assigned_/8_IP_address_... ) Whereas countries like India and China are lacking IP addresses. Until the address shortage starts to affect the aforementioned governments and corporations, I doubt we'll see any significant movement.

I can't source this, so disbelieve it if you like, but Comcast and others are seriously looking at IPv6. The reason is basically that they know what a pain it is going to be to switch. They want to get a head start, because they know that sometime they're going to ask for some new IPs, and actually be told "No."

The trick is that v6 isn't useful unless both the clients, servers, and networks are doing it. Comcast and others will need to push on Level 3 and others. Fortunately, they're big enough that they can play the "I hope nobody else does this before you; we might need to buy transit from them" card.

Dan Bernstein mainly describes that it is currently very hard to switch over. I would add to that that there is currently no reason whatsoever for an existing user to switch. Running out of address space is not a problem for an existing user.

Also there is no real "killer app" for IPV6. When they started with IPv6, there was a vision that it would solve all the hard problems that we currently have with networking: address space, multihoming, and mobility of both users and applications. However, all the zealots in the IETF made sure that IPv6 is as compatible to IPv4 as possible, thus it only solves the depletion of addresses.

Also, there is no guarantee that the routing mess that we currently have with BGP will magically go away when we switch over to IPv6. There are already signs that that problem is only going to get worse.