BGP, "Invalid NEXT_HOP attribute"

[Lexi Winter]

Ondrej Zajicek:
> On Sat, Mar 15, 2025 at 11:07:04AM +0000, Lexi Winter via Bird-users wrote:
> > Mar 15 11:03:22 uk-myb-2 bird[60388]: nl-myb-1: Invalid NEXT_HOP attribute - neighbor address fd5b:a83:b06b:500::1
> > Mar 15 11:03:22 uk-myb-2 bird[60388]: nl-myb-1: Invalid route 172.20.212.0/26 withdrawn

> The message is generated during route export and means that the NEXT_HOP
> attribute for the route that would be announced to the neighbor is the
> same as the IP address of that neighbor. This is not valid, so BIRD sends
> a route withdraw instead of an update.

thanks Ondrej.  i thought these messages referred to incoming updates,
but this makes more sense.

however, i am unsure why BIRD would be trying to send such updates to a
neighbor.

neighbor fd5b:a83:b06b:500::1/nl-myb-1 is an EBGP confederation peer, so
the only way we could have a route with next hop of fd5b:a83:b06b:500::1
is because uk-myb-2 received this route from nl-myb-1, or from its IBGP
RR cluster peer that also peers with nl-myb-1.

but in that case, nl-myb-1 ASN should be in confederation AS set of the
route, so we should not try to advertise it back to nl-myb-1, i think?

does this indicate something wrong with my configuration, or am i
misunderstanding something here?

PS: i sent you a mail (not to the list) about my BFD-related core dump,
i didn't hear back from you so i'm not sure if you received it.