IPv6 next-hop with incorrect link-local address received

[Sebastian Neuner]

Hi all,

we currently have an issue, where Bird kind of misses the right config
option to fix.

So we have a Cisco (XR) router peering with Bird on a Linux server. It's
an eBGP-Session though a /127 link.

We're announcing a prefix from the Cisco to bird, which has a foreign
next-hop (i.e. not in this /127). Cisco apparently misinterprets RFC2545
(or has a bug, I'm still discussing this with TAC) and adds the peering
interfaces link-local address.

So now the next-hop in the BGP update looks like this:

>  Next hop network address (32 bytes)
>    Next Hop: xxxx:xxxx:c02::28
>    Next Hop: fe80::28a:96ff:fecc:c10

The GUA next-hop is correct and points to a VM on the server (i.e. not
on the /127). The link-local next-hop points to the Cisco.
Unfortunately, this is the one, bird uses to install the route in the
kernel.

Am I missing something? Can I work around this somehow?

Or would it make sense for bird to have a switch for that? Similar to
"missing lladdr ignore" which works outbound, it could be something like
"next hop lladdr ignore"?

Best regards,
Sebastian