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


On Thu, May 03, 2012 at 10:37:35PM -0500, David Young wrote:
> > 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.

In Cisco IOS, you have <n> independent routing tables, but you can
have routes pointing out of a routing instance by specifying a target
interface that belongs to another routing instance.  Like:

  ip route vrf BLUE gige3/6

so if "gige3/6" belongs to "vrf RED", the default route for packets 
in "vrf BLUE" will make them change the vrf.

What you cannot easily do in IOS is "keep the packets on the same box,
but have them change vrf" - but that's something, for example, Juniper
ScreenOS can do with their "virtual routers" - you can point a route 
at another vrouter, to make it jump routing tables

set vrouter "trust-vr"
  set route vrouter "untrust-vr"

(a "vrouter" is, basically, a collection of routing table entries plus
interfaces - same as a VRF in Cisco-Speak)

So, for example, you could have one network, which is
reachable from all the virtual routing systems

set vrouter "vr-blue"
  set route vrouter "vr-management"
set vrouter "vr-green"
  set route vrouter "vr-management"
set vrouter "vr-yellow"
  set route vrouter "vr-management"

set vrouter "vr-management"
  set route interface ethernet0/3 gateway

(or so)

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