RE: network controls are necessary

["Joel M. Halpern" <joel@stevecrocker.com>]

Expecting hosts to have useful logic to perform source address selection 
seems a recipe for trouble in multiple regards.
Recognizing and selecting link local addresses is probably not an 
issue.  But as soon as you step beyond that, things break.  They break in 
two different ways at once.

In one regard, you end up needing significantly more logic in the host to 
make any kind of intelligent choice.  This means more code, more state, and 
more things for the network administrator to configure (probably incorrectly.)
Secondly, you couple the hosts into the behavior of the rest of the routing 
system, reducing the ability of the system to cope with changes (either 
network changes or protocol changes.)

If we really want the hosts to make the choice (a concept I am doubtful of) 
I suppose we could invent a query / response protocol for the purpose of 
asking a routing intelligent server what source /dest pair from a given set 
of sources and dests would be a good pair to use.

I strongly prefer the notion that other entities in the system would make 
the intelligent choice about the source address to use, and could change 
that choice as necessary.

Yours,
Joel M. Halpern

At 08:46 AM 12/6/2002 +0100, Erik Nordmark wrote:
> I did not suggest that hosts should run BGP. That would be completely silly.
> But IPv6 hosts are supposed to have a source address selection table
> according to a draft in the IPv6 WG (soon RFC).
> If the exit routing policy can be expressed with a few rules it
> would essentially be additional rules in that table (and a protocol
> by which the hosts can learn those rules).
> Hence my questions on the list (so far without answer) about reasonable
> sizes for the exit router selection policy/routes.
>
> > a) The hosts to have the same routing capabilities as routers currently
> > have.
>
> Sorry I don't follow the logic. The hosts don't route. Hosts with multiple
> source locators that talk to a node with multiple destination locators
> just do a selection e.g. when creating a new connection.