-----Original Message-----
IPv6 - while it has just over a decade of work, still has a long way to go to fulfill its promise. For the oldtimers, remember that it took IP a couple of decades to "gel" at version 4. Sure, we can (and in some cases - MUST) cram the "Internet" model on IPv6, but that is a genuine waste of opportunity.
So ... can we let an IPv6-based "polyphonic-net" embrace, and subsume the old, last century Internet? Or is that asking too much of the sales/marketing droids?
Most of the problems I have seen with v6 really aren't v6 problems. Programs and their various libraries, for example, that parse an address with a colon as a hostname is one example. Now I could even work around that by populating the local default dns domain with records that resolve to AAAA records ... if I could put a colon in a hostname (e.g. someone enters fe80::1e:dead:beef:cafe, the program looks up fe80::1e:dead:beef:cafe.my.local-domain rather than trying to connect to fe80:1e:dead:beef:cafe and dns returns with the AAAA record, that problem fixed, but I can't, so it isn't.) And even that would only work for a few commonly accessed hosts. Programs that rely on multicast will be a little different but that can be handled in dual-stack, at least in the local internal net. Now the problems with things like load balancing is real. Our vendor supports front end v6 VIPs balanced to backend v4 servers, but it requires a code update that must be tested before deployment and an outage scheduled once it has been tested. It isn't something that can just be thrown out there on a whim. The biggest cultural change is coming out of RFC1918 dungeons into the light of internet routable space and how people deal with that. It will be a very interesting time for networks, their vendors, and the engineers/techs/administrators.