[OLSR-users] olsr and the default gateway

[Thomas Lopatic]

Hey Stefan,

> is there a way to prevent olsrd from setting the default-route?

No, not currently, I am afraid. But what about adding a default route
with a better metric than what olsrd uses? I would expect Windows to
then use your manually added default route instead of the one created by
olsrd.

[...]

> Same question extended: can the local olsrd be forced to use one
> predefined default-route? In a network with multiple internet-gateway
> routing can be a problem it the LQs change and the preferred
> default-route changes with it.

Pre-defining a default route on your node wouldn't solve your problem,
as you only control which node you hand your packet to and not via which
further nodes your packet is routed. Let's assume the following topology.

  B-C
 /|
A |
 \|
  D-E

A is your node, C and E are Internet gateways. Suppose that you would
like to use C as your gateway. All you can do now is to send you packet
to B. It is, however, up to B to forward it to C or to D.

The idea in link state routing is that all nodes in the network agree
that C is the "best" gateway for A. So, A knows that C is its gateway
and B does so, too. If A sends a packet to B, it can rely on B sending
it to C. So, the idea is that all nodes cooperate according to a given
master plan.

So, if you wanted to pre-select a gateway, i.e. if you wanted to modify
the global master plan, you would have to tell everyone in the network,
so that again all nodes work according to the same master plan. You
would have to, for example, tell B that packets to the Internet should
be routed to C.

An alternative that is not routing-based would be tunneling. Establish
an IP-in-IP tunnel between A and C and make the default route point to
the tunnel. All your Internet-bound packets will then be tunneled to C,
decapsulated there and then transmitted into the Internet.

-Thomas