Re: Thinking about "branes" for netbsd...

[David Young <dyoung%pobox.com@localhost>]

On Fri, May 04, 2012 at 09:46:24AM +1000, Darren Reed wrote:
> On 4/05/2012 3:43 AM, David Young wrote:
> > The general idea is to have more than one forwarding domain per router.
> > Belonging to each forwarding domain are the routes for that domain and
> > some interfaces.  Each route/interface can belong to just one domain.
> > Packets cannot cross from one forwarding domain to another except by
> > going through an interface.  We can imagine a virtual interface that has
> > two "ends," each end in a different forwarding domain, for shuttling
> > packets from domain to domain.  More commonly we will have a hardware
> > interface that attaches a NetBSD router's forwarding domain to the
> > forwarding domain of a router/switch that's connected with an ethernet
> > cable.
> 
> Except for the notion that a route can belong to one domain,
> this is otherwise in agreement with what's proposed. More
> than one domain may have a specific route, for example, two
> domains may have the same default route.

How/why do two domains share a route, even the default?

It might help to see a made-up routing table for a couple of domains.

> > ISTM that it will be useful sometimes for a tunnel interface to straddle
> > two domains, sending/receiving encapsulated packets on one domain and
> > sending/receiving decap'd packets on the other.
> 
> And what if you have three domains?
> Do you then need n-1 tunnels in each domain to route between them?
> That doesn't scale.

I don't intend for anyone ordinarily to use tunnels---e.g., gre(4) or
gif(4)---to route between domains.  That is, the two-ended interfaces I
mentioned are not the same as tunnels.

I'm not sure what problem you are trying to solve by routing each domain
to every other domain, but I suppose that the two-ended interface
posited above could be N-ended or else you could route each domain to a
central domain:

+------+            +------+
|      |            |      |
|      |\          /|      |
|      |  +------+  |      |
+------+  |      |  +------+
          |      |          
+------+  |      |  +------+
|      |  +------+  |      |
|      |/          \|      |
|      |            |      |
+------+            +------+

Then again, source-routing may be what you need?

Anyway, I'm not too keen on routing domains to each other in the same
box.

Dave

-- 
David Young
dyoung%pobox.com@localhost    Urbana, IL    (217) 721-9981