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

[Alexander Zubkov]

Hi,

Please show also:
show interface
show route all

So when you have both bgp_v6_a and bgp_v6_b established - you have
normal routes. And when you have only bgp_v6_a established - you have
that unreachable route only?
Your bgp sessions are internal (iBGP), so they may probably have
bgp_nex_hop different from the router's address. And also because of
recursive resolution they may depend on other routes you have in your
bird.

On Sat, Apr 10, 2021 at 8:02 PM Dez C <dez at otenet.gr> wrote:
>
> Hi,
>
> all external routes were unreachable (apart from the local loopback
> which was imported via direct protocol). master6 consisted solely of
> entries like:
>
> 2a02:xxxx:d00d::/45 unreachable [bgp_v6_a 19:38:23.222 from 2a02:xxxx:yyyy:53::a] * (100) [ASxxxxx1i]
>
> No entries whatsoever from the other bgp session (bgp_v6_b), like in
> normal operation:
>
> 2a02:xxxx:d00d::/45   unicast [bgp_v6_a 2021-04-07] * (100) [ASxxxxx1i]
>          via 2a02:xxxx:yyyy:53::a on eth2
>                       unicast [bgp_v6_b 2021-04-07] (100) [ASxxxxx1i]
>          via 2a02:xxxx:yyyy:53::b on eth2
>
>
>
> regards,
> Yannis
>
>
> On 4/9/21 11:22 PM, Alexander Zubkov wrote:
> > 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
>