In message <20100127160401.1a963a56@opy.nosense.org>, Mark Smith writes:
Sure. However I think people are treating IPv6 as just IPv4 with larger addresses, yet not even thinking about what capabilities that larger addressing is giving them that don't or haven't existed in IPv4 for a very long time. People seem to be even ignoring the maths of how big a single /48 is, just in terms subnets. I've never worked on an individual network with 65K subnets (with the Internet being a network of networks), and I doubt many people on this list have. Yet people seem to treating a /48 as though all networks will have 65K subnets, and therefore they'd better start of using longer than /64s because they might run out of subnets.
I care about this because I don't want to see people have to change their addressing in the future to /64s, because of that will typically involve a lot of out of hours work (which could include me if I inherit a network that has had longer than /64s deployed (there's my bias)). I'd prefer to see people go the other way - deploy /64s everywhere, as per the IPv6 Addressing Architecture, and if that proves to be the wrong case, then go to the effort of deploying longer prefixes. I think going from /64s to longer prefixes is far less likely going to be needed than the other way around.
And if you have more than 65K networks you have the justification for a second /48 at which time you can decide whether to request a /47 and renumber into it or just use two non-contiguous /48's. Mark -- Mark Andrews, ISC 1 Seymour St., Dundas Valley, NSW 2117, Australia PHONE: +61 2 9871 4742 INTERNET: marka@isc.org