Issues establishing more than 2 BGP sessions

[Vincent Bernat]

 ❦ 11 novembre 2017 23:44 -0600, Chris Stein <bksteiny at gmail.com> :

> Individually, bird is able to establish a session on both tunnels at every
> remote VPC, so I know that works. Occasionally, I have noticed that
> established connections will disconnect with a “Hold timer expired”.
> There’s something I’m missing/overlooking in the config to allow all
> sessions to be active.

I think BIRD is receiving a remote route that would replace the route
used to reach the neighbor. Are you using route-based tunnels (with VTI
interfaces)? If yes, "ip route show" output would help to
understand. Otherwise, "ip xfrm policy" would help.

If you want a working setup similar to yours (a tad more complex since
it involves multiple routing tables), here is one:

 https://vincent.bernat.im/en/blog/2017-route-based-vpn
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