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Re: A Good Schism Brightens Anyone's Day (was: A Simple Question)

2003-04-30 10:12:09
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



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