IGP(OSPF) learned route not used for iBGP?

[Ondrej Zajicek]

On Fri, May 12, 2023 at 05:15:43PM +0200, Nico Schottelius via Bird-users wrote:
> 
> Hello fellow bird users,
> 
> a quick IGP/iBGP question:
> 
> Why does apu-router1 that should learn the IPv6 default route from
> server138 complain about not accepting the route?
> 
> May 12 17:13:18 apu-router1 daemon.err bird: server138_v6_v4: Invalid NEXT_HOP attribute - address 2a0a:e5c0:32:2::21 not directly reachable
> May 12 17:13:18 apu-router1 daemon.err bird: server138_v6_v4: Invalid route ::/0 withdrawn
> 
> Checking that apu-router1 has the route:
> 
> bird> show route 2a0a:e5c0:32:2::20/124
> Table master6:
> 2a0a:e5c0:32:2::20/124 unicast [ospf6 17:14:01.612] * E2 (150/10/10000) [0.0.0.138]
>         via fe80::3eec:efff:fed2:d0c2 on eth1.2 weight 1
>         via fe80::3eec:efff:fed2:d0c4 on eth2 weight 1
>                      unicast [server137_v6_v4 17:13:19.524] (100) [i]
>         via 2a0a:e5c0:0:b::89 on eth2
>                      unicast [server138_v6_v4 17:13:18.394] (100) [i]
>         via 2a0a:e5c0:0:b::8a on eth2
> bird>
> 
> The complete setup is as follows:
> 
>     apu-router1 -- server138 -- [wireguard] -- server120
> 
> - apu-router1 and server138 are ASN 199553 [iBGP)
> - server120 is 209898 [eBGP]

Hello

Considering that route for 2a0a:e5c0:32:2::20/124 is at apu-router1, my
guess is that your IBGP link is configured as 'direct', which implies
'gateway direct' processing of bgp_next_hop attribute, expecting it to
be directly reachable on apu-router1, not indirectly through OSPF route
(like with regular IBGP).

Either set 'gateway recursive' option in IBGP channels on apu-router1, or
set 'next hop self' in IBGP channels on server138.

What is your IBGP config on apu-router1?

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."