Recursive nexthop via kernel route in proto static not working

[Daniel Gröber]

Hi Alexander,

On Tue, Jun 27, 2023 at 04:48:46PM +0200, Alexander Zubkov wrote:
> Not sure, but I would guess it can be related to the local address. It
> might try to pick the first interface with such network.

> Could you try your setup with some route that has the nexthop from a
> unique subnet configured on the interface? At least to check if it will
> become reachable or not.

Ok, if I add a route like `2000::/64 dev enp1s0 via
fe80::fc00:3ff:fec7:cd05` to the kernel and recurse through that it does
work.

    protocol static static_export_kernel2 {
        ipv6;
        igp table master6;
        route 2001:db8::/64 recursive 2000::1234;
    }

    $ ip -6 route add 2000::/64 dev enp1s0 via fe80::fc00:3ff:fec7:cd05
    $ birdc show route protocol static_export_kernel2 all
    2001:db8::/64        unicast [static_export_kernel2 16:01:20.131] * (200)
            via fe80::fc00:3ff:fec7:cd05 on enp1s0
            Type: static univ

> Or it might be that routes imported from the kernel are marked as
> recursive, so it does not resolve because Bird does not allow double
> recursion.

If I remove the 2000::/64 route the recursive route goes back to
unreachable. So something seems to be preventing recursion through the
default route specifically, but it evidently doesn't have anything to do
with the route coming from the kernel.

    $ ip -6 route del 2000::/64 dev enp1s0 via fe80::fc00:3ff:fec7:cd05
    $ birdc show route protocol static_export_kernel2 all
    2001:db8::/64        unreachable [static_export_kernel2 16:01:20.131] * (200)
            Type: static univ

Weird.

Thanks for your suggestions,
--Daniel