occasional stalls of a WG tunnel

[Michael Tokarev <mjt@tls.msk.ru>]

Hi!

We're experiencing occasional stalls of a single (so far)
node in a star-like configuration.

The server in the center is a linux system with kernel 5.10.13
with a built-in wireguard module.  The client is a windows machine
with current wireguard software installed from the site.

Sometimes (which happened 3 times already), the tunnel stops
working, - no traffic goes within the tunnel as far as I can
see.  I'm not sure yet if the encrypted packets are flowing
between the two nodes, - at least the linux system is sending
them but I can't say for sure if the windows system does the
same, - this is something for me to watch the next time it
happens.

What can cure the tunnel immediately is a simple "refresh"
command, -

  wg setconf $if /etc/wireguard/$if.conf

- this makes the whole tunnel operational again immediately.

Other nodes of the tunnel are unaffected by this (except of
the momentary drop of service during the setconf operation
and the reconnect each node is doing after that).

The question is: how can I debug what's going on the next
time this happens, besides watching more closely which packets
are flowing?

Thanks,

/mjt