Thus spake "Keith Moore" <moore(_at_)cs(_dot_)utk(_dot_)edu>
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.
IMHO, dialup is a bad example because static IPs per customer are rare;
let's switch to the cable/dsl market.
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. The latter might
be justified if we're truly committed to eliminating NATs, but it costs a
lot more in routes, in administration, and in address waste (assigning a /48
to what is, in nearly all cases, 1-4 hosts).
S
Stephen Sprunk "God does not play dice." --Albert Einstein
CCIE #3723 "God is an inveterate gambler, and He throws the
K5SSS dice at every possible opportunity." --Stephen Hawking