Re: [homenet] draft-boutier-homenet-source-specific-routing-00

[Henning Rogge <[e-mail]>]

On Wed, Jul 10, 2013 at 2:59 PM, Juliusz Chroboczek
<[e-mail]> wrote:
>> Still, as long as the different destinations for the source-routed
>> default-routes are in a source-route aware subnet it should work.
>
> Could you please clarify.  Have you identified another case where
> everything works out?

I am looking at the problem from the link-state point of view.

Lets assume there is a random mixture of source-routing aware and
non-aware routers. The only restriction is that there is a
source-aware path of routers between all gateways (gateways to the are
of course source-aware too).

There are two topologies in the network, the default topology all
routers participate in and a "source-aware" topology.

I see three cases when forwarding an IP packet with a "specific source
address" along the default route.

a) the router is not source-routing aware, which means it forwards the
packet along the normal default route
b) the router is source-routing aware, but has no source-aware path
towards the gateway. In this case it will still forward the packet
along the normal default route because it has no connected path to the
gateway selected by the source address (shortest path first result
should be empty).
c) the router is source-routing aware and has at least one path
towards the selected destination. In this case it will forward the
packet towards the selected gateway. The next hop will also be
source-aware, otherwise the link would not have been selected for the
"source-aware" topology.

Every non-source-aware default route will bring the traffic into the
source-aware region around the gateways, which mean they should reach
the desired gateway (even if it hit a different gateway first).

This should work with or without dropping data on the source-aware
topology on the non-source-aware routers.

Henning Rogge

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