BFD not recovering after link recovers

[Ondrej Zajicek]

On Wed, Jan 27, 2021 at 03:23:25PM +0000, 0.bgp at elloe.vision wrote:
> We are setting up a container based proof of concept with IPv6 only using
> ECMP, ANYCAST, BGP with BFP and Bird2 and I've hit a problem where BFD
> doesn't recover after a local link goes down and comes back and are seeking
> some advice as whether this is expected behaviour or a bug.

Hi

Based on quick evaluation, seems to me that it is a combination of race
condition in BIRD and systemd-networkd behavior. There is a condition in
BIRD that when a BFD session is added during the time IP address on that
link is added/removed, sometimes it fails to add the socket.

Seems like this issue is exaggerated by systemd-networkd, as normally it
happens just during admin-up/down events, but from the logs it seems that
as a reaction on link-up/down, systemd-networkd adds/removes the IP address.

-- 
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."