

On Wed, Aug 15, 2007 at 02:16:31PM -0400, James Carlson wrote:
> Ole Troan writes:
> > >> If you delegate a prefix, then you route to the prefix -- best match.
> > >
> > > Yes, but how does that route get in the table, and what next-hop is
> > > set?  You have to know your customer's address eventually.
> > 
> > next-hop is the link-local address though.
> 
> Right; it's the link-local address of the router to which you've
> delegated the prefix.

Well, sometimes.  It depends what you're doing.

Either way:  You need to know the customer's address.  A DHCPv6 server
off in the weeds does not necessarily know what link local address the
client is using (because it might change without notification).  It
may know what global addresses the client is using (because it
allocated them), but won't if router solicition is in use.  A
router solicitation system certainly doesn't have any knowledge of
which customer is which nor what addresses global or not which they're
using.

This is but one facet of a network's operation: try not to focus on
it too much.  There are potentially a multitude of reasons to know
which of your customers are online, and how to reach them.  Testing
connectivity alone (such as during a support call).

> It's not the address of every single machine on the customer's
> network.  In fact, knowing the addresses of the machines on the
> customer's network is useless, as it doesn't tell you the address of
> that CPE router.

I'm not sure why you make this declaration (twice now), when no one
has suggested the counterpositive.  Maybe I misunderstood Iljitsch.

> Obvious sorts of ways to get this would be to keep track of your
> delegations or (alternatively) use an appropriate routing protocol.

Which I think gets us back to what Iljitsch said in the first place,
except that realistically ISPs are going to find it difficult and/or
costly to trust routing information from eg broadband customers, so
really what you're looking at is some way to provide a register of
your customers' current addresses.

-- 
Ash bugud-gul durbatuluk agh burzum-ishi krimpatul.
-- 
David W. Hankins	"If you don't do it right the first time,
Software Engineer		     you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins
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