i suggest ietf.org mail server to operate in IPv6 only. > > 6to4 is now widely deployed > > Is it? Can you cite any data? - Apple MacOS X implements it. i'm not sure which release started shipping it, but if it was from 10.2, there are 22 million copies around, with IPv6 enabled by default. - Apple AirPort Exterme implements it. > > The /48 prefix length is not just some knob that RIRs or ISPs can turn > > at their will. It's a constant that's embedded into 6to4 protocol > > implementations in tens or hundreds of millions of computers. > > Give me a break. Use leading zeros for the first 8 bits of the subnet > part and everything else still works just fine. so if you are running 6to4 enterprise (/48) and then get some prefix from ISP/RIR which is like /56, you would have to renumber entire subnet portion to fit into 8 bits, from 16 bits. imagine how painful it is, and imagine how it will constrain people from exiting from 6to4 addresses to real IPv6 addresses. itojun _______________________________________________ Ietf@xxxxxxxx https://www1.ietf.org/mailman/listinfo/ietf