Host not reachable over UDP

[Petr Man]

Dear all,

I have been successfully running for quite some time a tinc 1.1 network in
switch mode. I recently added a new node, that refuses to communicate over
UDP.
Running "tinc info mynode" from a different box returns:
Reachability: directly with TCP

It appears that tincd is not listening on UDP port 655 on "mynode". Running
"ss -nlptu | grep tincd":
tcp    LISTEN     0      3         *:655                   *:*
      users:(("tincd",pid=10097,fd=6))

In the log there is a large number of these messages:
Received UDP packet from unknown source 123.321.123.321 port 655

I am puzzled how is tincd getting the packets if it is not listening on
655/UDP.

When I start netcat on the node on port 655/UDP I can see garbage coming in
from the other nodes trying to initiate an UDP connection.

Would you have any hints where to start debugging this? All machines are
configured the same way and work fine (various linux versions, windows).
This particular box is on Ubuntu Xenial kernel 4.3.5.

Best,
Petr
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