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

[Darren Reed <darrenr%netbsd.org@localhost>]

David Young wrote:
> 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?

Sharing a route is not the same as having the same route.

So I do not see routes being shared but I do see more than
one brane needing to have the same route. So perhaps "belong"
is the wrong word to use, but the same route can be present
in more than one brane at any one time.

A very basic instance of this would be different interfaces,
with different IP addresses, each in their own brane. Thus
each would necessarily require the network route that uses
the interface.

> > > 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:
...

I'm not trying to solve a problem per se, rather I'm testing
the soundness of the proposal that was put forward, which is
to say that it didn't scale linearly (i.e. it is bad.) Using
a central domain is a better idea.

Darren