You mean your _current_ anycast relay is at 70ms ;) That might change overnight. Next to that, in case of problems, you won't be able to debug them easily. Because of the anycast nature of 6to4 relays, the path that packets might flow can be so various and ever changing that it is nearly impossible to debug; unless you have access to every hop on the network, which I think you can guess the answer for, you most very likely don't have this, and otherwise you would most very likely do native IPv6 over those links. As you are located in Ireland, you will most likely get tunnels from HEAnet who are doing an amazing job with IPv6 connectivity and have good monitoring in place. Capacity is also not a problem there either. This is actually the same for all other PoPs. If one looks at the traffic stats you can see that even if we would use a single PoP for everybody a 100mbit link would be enough. With nearly 30 PoPs though, there is much more capacity than that and some PoPs even are connected per 1GE and 10GE links, the only overhead can thus be in the tunneling protocol used (fi, AYIYA has some due to it's implementation). As for connecting servers over tunnels. If you have several servers in one location, one should request one tunnel and a subnet and route the subnet over them. If you want failover, you can always use the heartbeat protocol and fail the tunnel over to another host by enabling it there. Of course that doesn't solve the rest of the path issues that might be there then, but it does solve the 'one box goes down on my end' situation. The real solution is of course going native, but where that is not possible and one wants to get IPv6 today, so that one is ready when the native connectivity comes and/or customers start to ask about it, just tunnel over the last part of the infrastructure that is not IPv6 enabled yet.

I can't get to http://www.kame.net/ with 6to4. This leads me to believe that 6to4 is not as universal as a tunnel. But it is very anecdotal evidence. I would go for the tunnel. 6to4 feels like a hack. A tunnel is also a hack I suppose, but it is a constant tunnel sounds a lot more consistent than a renew-every-connection relay. Besides, 2002::/16 seems to announce "hey, I can't get a real IPv6 address!" to your clients.