OSPF route in database not imported in table

16 Sep 2021

      Ave,

I am observing behavior that I do not understand on two of our bird
instances, maybe you guys can help me make sense of it. I'll start by
giving you an overview of our setup, then I'll describe the problem and
paste some configuration snippets.

We have three pairs of routers connected over a meshed VPN, each pair
being in a different physical location. These routers are connected to
the wider internet, to the inter-location mesh VPN and to stub networks
to whom they provide connectivity. We use BGP sessions at each site with
our local upstream to obtain and export routes, and OSPF over the mesh
VPN for internal routing. Everything is dual-stacked, but the issue I am
observing is only over IPv4, so let us only consider IPv4.

Calling the three locations A, B and C, I have the following problem: C
exports a /30 prefix via OSPF (gathered by the automagic generation of
stub networks). A and B correctly recieve it and display it in the
`birdc show ospf state <ospf ipv4 name>` map, but while it is correctly
imported into the master4 table in B, it does not appear in the master4
table in A. Both configurations are, as far as I can tell, identical for
all relevant purposes. Versions of bird, operating system and kernel are
the same.

Relevant birdc output:
```
show ospf state ospf4:
[...]
router 0.0.2.1
	distance 10
	network [0.0.2.1-6] metric 10
	stubnet xx.xxx.xxx.x/30 metric 10
```

```
show route table master4 protocol ospf4:
Table master4:
	[...]
```
where the second output does not contain the required /30.

Relevant configuration:
```
protocol ospf v3 ospf4 {
	description "backbone OSPF v4";
	instance id 64;

	ipv4 {
		import all;
		export none;
	};

	area 0 {
		interface "tun0";
		interface "vlan10";
	};
}
```

The main difference between A and B are the routes that they recieve over BGP
from our upstreams: one of them contains a 0.0.0.0/0 default route (A) and the
other does not, only the list of IPv4 routes.

I am at loss as to why the route is not imported into the master table,
so any advice or suggestions would be very welcome.

Vale,

-- 
Joachim Desroches