ospf uses private ip as a gateway

[Ondrej Zajicek]

On Sun, Mar 20, 2011 at 03:56:02AM +0100, Martin Kraus wrote:
> Hi. I'm using bird 1.2.5 from debian squeeze respository.
> I've got two routers with public a private ip addresses on the connecting
> interfaces. The public addresses are selected as primary in device protocol but
> ospf chooses private address as the address to route prefixes over. When I block
> ospf packets from the private addresses it switches fine but when I allow ospf to
> them it switches all the routes to the private gateways again. 
> 
> Is there any way to force bird to use public addresses other then setting them as
> primary in device protocol specification? I want to keep interface names in
> interfaces definitions instead of ip addresses.

For a while, BIRD handles more addresses on one iface as a virtually
separate ifaces/networks (that is, AFAIK, the same way as Quagga handles
that). You can check that with 'show ospf interface'. So in your case,
you got two adjacencies between the routers with the same cost and it is
up to a chance which will be chosen as a route. When you blocked private
addresses, one adjacency broke.

The primary setting in device protocol does nothing for OSPF, because
OSPF now does not handle primary addresses in a special way. That was
a kludge before we got proper multi-address support. [*]

So you would need to specify addresses (or at least prefixes) in
interface definitions. See http://bird.network.cz/?get_doc&f=bird-3.html#dsc-iface
for details. You could either add prefixes to interface definitions
to restrict application of that definitions on the public addresses,
or you could add something like this as the first definition:

interface 192.168.0.0/16 { stub; };

That would match all private addresses and change that to stubs,
public addresses get over that and matches with later definitions.


[*] That is true for Linux. On *BSD, we still have the old behavior and
generally multi-address support is problematic there.

-- 
Elen sila lumenn' omentielvo

Ondrej 'SanTiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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