Received route with strange next-hop

[Adrichem, N.L.M. (Niels) van]

Hello,

I'm trying to redistribute routes from another routing daemon through synchronization of the kernel table using the kernel protocol in BIRD 2.0.4. However, I run into some problems that not all routes are imported by the BIRD router.

The kernel routing table contains the following routing table:
# ip route
10.0.0.0/24 dev eth0 proto kernel scope link src 10.0.0.1
10.0.1.3 via 10.0.1.4 dev eth1 proto zebra metric 2
10.0.1.4 dev eth1 proto zebra scope link metric 1
10.0.4.0/24 via 10.0.0.2 dev eth0 proto bird metric 32

The interface eth1 has the address 10.0.1.1/32 in an ad-hoc routing domain, through OSPF-MDR (which is an extension of Quagga) it finds the direct neighbor 10.0.1.4 which is added as "10.0.1.4 dev eth1 proto zebra scope link metric 1". The neighbor 10.0.1.4 advertises that it can forward to 10.0.1.3 which is added as "10.0.1.3 via 10.0.1.4 dev eth1 proto zebra metric 2". The routing of OSPF-MDR works, in the sense that 10.0.1.1 can reach 10.0.1.3 and 10.0.1.4.

However, when we try to import these routes from the protocol kernel into the Bird routing table, only the directly connected route to 10.0.1.4 shows while the route to 10.0.1.3 are not imported:
# birdc show route
BIRD 2.0.4 ready.
Table master4:
10.0.1.4/32          unicast [kernel1 10:27:29.329] (10)
                dev eth1
10.0.4.0/24          unicast [babel1 10:27:23.461 from fe80::200:ff:feaa:4] (130/96) [00:00:00:00:0a:00:00:02]
                via 10.0.0.2 on eth0
10.0.0.0/24          unicast [direct1 10:27:21.870] * (240)
                dev eth0
                     unicast [babel1 10:27:23.461 from fe80::200:ff:feaa:4] (130/96) [00:00:00:00:0a:00:00:02]
                via 10.0.0.2 on eth0

Additionally, the bird.log file throws the following error:
2019-05-15 10:27:21.869 <INFO> Started
2019-05-15 10:27:21.902 <WARN> Missing broadcast address for interface vxlan0
2019-05-15 10:27:29.329 <ERR> KRT: Received route 10.0.1.3/32 with strange next-hop 10.0.1.4

It may be that kernel protocol rejects the route because the next-hop is not in the interface its regular netmask (which is set to /32), though I am not familiar enough with the source code to determine the exact cause except that the error gets thrown from sysdep/linux/netlink.c line 1643. However, I think the line should be accepted since there is another routing rule confirming that the next-hop is directly attached to device eth1. Given the explicit error I don't think this is a configuration error (though I am open to learn more), so I hope BIRD can be patched to solve this.

I have attached the bird.conf file, as well as an image of the example topology. Above snippets and config file are taken from node n1 which is running both the OSPF-MDR router based on Quagga and BIRD Router.

Any help would be much appreciated.

Thanks in advance,
Niels van Adrichem

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