1 out of 2 BGP sessions down, all routes become unreachable

[Alexander Zubkov]

Hi,

And what do you see in your bird's console? "show route" etc.

On Fri, Apr 9, 2021 at 7:10 PM Dez C <dez at otenet.gr> wrote:
>
> Hello,
>
> First message here, although a long-time bird user (not an expert in any
> way). We're using bird as a bgp speaker for all our VMs that either need
> to announce routes or import routes from VRFs etc.
>
> The setup is pretty straight forward I'd guess. The VM has 2 IPv6 BGP
> sessions with 2 L3 switches (one per switch). The VM announces one /128
> route and imports all routes learned from the BGP sessions. The same
> routes are learned from both sessions, so whenever I do a 'ip -6 r' I
> see 2 entries for each route (with different next hops) like:
> 2a02:xxxx:d00d::/45 via 2a02:xxxx:yyyy:zz::a dev eth2 proto bird metric
> 32 pref medium
> 2a02:xxxx:d00d::/45 via 2a02:xxxx:yyyy:zz::b dev eth2 proto bird metric
> 32 pref medium
>
> At some point, both BGP sessions went down and one of them did not
> recover for an hour. Normally, this should not be a problem but in this
> specific case, I could no longer see 2 routes in the kernel table, one
> reachable and another unreachable, just an unreachable one, so even
> though the anycast route was being announced and traffic was reaching
> the VM, it couldn't send the packets to their destination as all routes
> were unreachable in the kernel table:
> unreachable 2a02:xxxx:d00d::/45 dev lo proto bird metric 32 error -113
> pref medium .
>
> I'm running 2.0.7 (upgrading soon) on centos7 and here's the relevant
> part of my config:
>
> protocol device {
> }
> protocol direct direct_v6_lo {
>          interface "lo*";  # announce loopback
>          ipv6;
> }
> protocol direct direct_v6_eth {
>          interface "eth*";
>          ipv6;
> }
> protocol bgp bgp_v6_a {
>          local 2a02:xxxx:yyyy:53::37 as 66666
>          neighbor 2a02:xxxx:yyyy:53::a as 66666;  # switch A
>          ipv6 {
>                 export where proto = "direct_v6_lo";
>          };
> }
> protocol bgp bgp_v6_b {
>          local 2a02:1388:4000:53::37 as 66666;
>          neighbor 2a02:1388:4000:53::b as 66666;  # switch B
>          ipv6 {
>                  export where proto = "direct_v6_lo";
>          };
> }
> protocol kernel {
>      ipv6 {
>          export filter {
>              if proto = "direct_v6_eth" then reject;
>              accept;
>          };
>      };
>     merge paths limit 2;
> }
>
> any ideas?
> thanks in advance and regards,
> Yannis