> > this is an interesting point, but I think it has more to do with > > whether the prefixes are statically bound to customers than the > > length of those prefixes. why would giving customers static /64s > > result in fewer routes in your IGP than giving them static /48s? > > in neither case is there a direct correspondence between the > > customer's address and the concentrator. > > IMHO, dialup is a bad example because static IPs per customer are > rare; let's switch to the cable/dsl market. well, they might not be so rare in the IPv6 market, but whatever... > Standard practice is to connect all customers in a given area (or > signed up in a given period) to a single concentrator via some sort of > virtual circuit(PPPoE, ATM, FR, etc). This concentrator then > internally bridges all of these virtual circuits into a single subnet > with a single prefix, giving you one route for N customers. OTOH, if > you assign a prefix to each customer, you then have between N+1 and 2N > routes for N customers. well, for cable at least, seems like you'd want to assign a prefix to each concentrator and give each customer a /48 subnet out of the concentrator that serves that location. as I understand dsl it affords more flexibility than that, since each customer can get a VC to a concentrator which can essentially be anywhere, but you'd still want to assign an appropriate-sized prefix to the concentrator and dole /48 subnets out of that. either way you get to do route aggregation at the concentrator. I suspect a lot of "standard practice" for IPv4 is designed to conserve address space; it's not clear that such practices are either desirable or optimal for IPv6. more generally, IPv6 is going to be driven by different markets, different applications, and a different set of customer demands than IPv4. so anytime you find yourself thinking that "standard practice" (meaning v4 practice) axiomatically applies to IPv6, it might be worth re-examining the assumptions behind that practice. Keith