Issue injecting network overlapping BGP next hop in bird6.

[João Taveira Araújo]

Hi,

I'm running into a difference in behaviour between bird and bird6,
although admittedly it may come from netlink itself. I'm using bird
1.5.0, but have also tried with build from latest git head.

Assume a connection to an upstream router over a link addressed with
10.0.0.0/31 or AAAA::0/127 for IPv4 and IPv6 respectively. For IPv4,
the upstream announces the follow prefix:

10.0.0.0/31     via 10.0.0.0 on eth0 [session 22:14:01] ! (100)
        BGP.next_hop: 10.0.0.0

In this case the route fails to be injected into the FIB, because a
route already exists from proto kernel, as the interface is addressed
from that prefix.

In IPv6, the same thing happens, but on restarting bird6 all routes
fail to get injected, each with the following error: "Netlink: No
route to host". If I filter out the route on clean boot, thereby
avoiding every attempting to inject the overlapping route, this does
not happen.

Cheers,
Joao