I am coming to you with a weird one. I have simple iBGP setup between two routers which are interconnect through VLAN on IPv4 (/30) PtP link. For now RTR1 has all of the BGP feeds. I wanted to pass it to RTR2. Config on RTR2 is pretty simple:

filter bgp_in
{
preference = bgp_local_pref;
accept;
}

filter bgp_out
{
if proto = "CORE" then accept;
reject;
}

protocol bgp RTR1 {
local xx.xx.xx.xx as PUBLICAS;
neighbor xx.xx.xx.xx as PUBLICAS;

ipv4 {
table master4;
next hop self;

import filter bgp_in;
export filter bgp_out;
};
}

As soon as session starts up it loads routes, then unloads them and resets bird process. And it happens again and again and again...

Logs doesn't seem very helpful:

Dec 18 12:36:14 RTR2 bird[2009]: Started
Dec 18 12:37:20 RTR2 systemd-journald[474]: [🡕] Suppressed 110623 messages from dataplane-bird.service
Dec 18 12:37:20 RTR2 bird[2009]: RTR1.ipv4: Export state changed from DOWN to FEEDING
Dec 18 12:37:20 RTR2 bird[2009]: RTR1.ipv4: Export state changed from FEEDING to PARTIAL
Dec 18 12:37:20 RTR2 bird[2009]: RTR1: State changed to up
Dec 18 12:37:20 RTR2 bird[2009]: RTR1.ipv4: Export state changed from PARTIAL to READY
Dec 18 12:37:20 RTR2 bird[2009]: RTR1.ipv4: Fed up
Dec 18 12:37:23 RTR2 bird[2009]: Netlink: Network is unreachable
Dec 18 12:37:23 RTR2 bird[2009]: Netlink: Network is unreachable
Dec 18 12:37:23 RTR2 bird[2009]: Netlink: Network is unreachable
Dec 18 12:37:23 RTR2 bird[2009]: Netlink: Network is unreachable
Dec 18 12:37:23 RTR2 bird[2009]: Netlink: Network is unreachable
Dec 18 12:37:23 RTR2 bird[2009]: ...
Dec 18 12:37:23 RTR2 bird[2009]: Kernel dropped some netlink messages, will resync on next scan.
Dec 18 12:37:23 RTR2 bird[2009]: Shutting down
Dec 18 12:37:23 RTR2 systemd[1]: Stopping dataplane-bird.service - BIRD Internet Routing Daemon...
Dec 18 12:37:23 RTR2 bird[2009]: RTR1: Shutting down
Dec 18 12:37:23 RTR2 bird[2009]: RTR1.ipv4: Export state changed from READY to DOWN
Dec 18 12:37:23 RTR2 bird[2009]: RTR1.ipv4: stop import: rr 2 set 0 valid 0 pruning 0 pruned 0
Dec 18 12:37:23 RTR2 bird[2009]: RTR1: State changed to stop
Dec 18 12:37:23 RTR2 bird[2009]: RTR1: State changed to flush
Dec 18 12:37:24 RTR2 bird[2009]: RTR1: State changed to down
Dec 18 12:37:24 RTR2 bird[2009]: Shutdown completed

I also tried running the same config, but by starting BIRD processes manually as a root in foreground. It was able to load the routes, but only if pointed ipv4 channel of bgp protocol to custom separate table. As soon as I passed it into my master4 table process crashed with segfault. Unfortunately without meaningful traceback.

I don't know if is important, but I use VPP as my dataplane.

Pozdrawiam,

Łukasz Jarosz