> Today, dial-up concentrators usually have an address > range that it used to assign addresses to people that dial in. That > means at most a handful of routes per dial-up concentrator in the > interior routing protocol. If everyone has their own /48, that means a > route in the IGP for each customer that's online. There are no hard and > fast rules about how many routes you can have in an IGP, but somewhere > between 10k and 1M you run into trouble. 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.