v6 subnet size for DSL & leased line customers

sthaug at nethelp.no sthaug at nethelp.no
Thu Dec 27 11:44:44 UTC 2007

> > "Configure this stuff manually" may work for a small number of
> > customers. It is highly undesirable (and probably won't be considered
> > at all) in an environment with, say, 1 million customers.
> Of course not. But RAs on a subnet with a million customers doesn't  
> work either, nor does DHCP on a subnet with a million customers.

It wouldn't be a subnet with a million customers, of course. We would
typically have aggregation routers handling 5000 to 30000 customers,
each connected via (in our case) point to point DSL links. Important
point here is that we *don't* want per-customer IPv4 (or IPv6) config
on the aggregation routers - this is what we have DHCP servers for.

> If we're talking about provisioning cable/DSL/FTTH users, that's a  
> completely different thing. Here, DHCPv6 prefix delegation to a CPE  
> which then provides configuration to hosts on its LAN side would be  
> the most appropriate option. However, the specifics of that model need  
> to be worked out as there are currently no ISPs and no CPEs that do  
> that, as far as I know.

I agree that DHCPv6 prefix delegation (for instance a /56) to a CPE
which provides configuration to hosts on its LAN side sounds like a
reasonable model. It requires the customer to have a CPE with actual
*router* functionality, as opposed to just a bridge. This is different
from today's requirements, but may not be unreasonable.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no

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