Inject default route via OSPF, but only to specific OSPF peer and contingent on BGP session established

[Ondrej Zajicek]

On Wed, Jan 10, 2024 at 10:02:49AM +0100, Lukas Haase via Bird-users wrote:
> Hi Maria,
> 
> Thank you for respecting. First of all, sorry for my duplicate message. (My browser crashed and I did not realize the email was sent)
> 
> > Gesendet: Mittwoch, den 10.01.2024 um 08:52 Uhr
> > Von: "Maria Matejka via Bird-users" <bird-users at network.cz>
> > An: bird-users at network.cz
> > Betreff: Re: Inject default route via OSPF, but only to specific OSPF peer and contingent on BGP session established
> > 
> > Hello!
> > 
> > TL;DR: That's currently not possible. But there are other options.
> 
> To me, my setup sounds like the most common, most normal configuration one could imagine. The fact that this sounds so troubling makes me think: Am I doing something conceptually wrong?
> 
> How would one implement my scenario?

In general, OSPF supposes that all routers in one area have the same set
of routes / network destinations, they are not announced to some specific
router, but to everybody in the area.

You wrote:

> Both border gateways act as default gateways for the internal router.
> In order to create redundancy, each border gateway should send the
> default route via OSPF to the internal router. However, the default route
> should not be sent to any other device (otherwise it would mess up
> everything, incl tunnels).

The other devices do not have a default route? Or use one from the
internal router? You could probably have separate area for gateways and
internal router, and another area (perhaps stub / NSSA) for one with
other devices, or just use IBGP as you suggested.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
"To err is human -- to blame it on a computer is even more so."