What's the possible cause of UDP probe failure?

[Bright Zhao]

>From the tinc log I can see: the client side(behind the firewall) never
receive the MTU probe from server side(public IP), so my question is what
is the packet looks like for the MTU probe packet? It's a UDP packet?
Source/destination of UDP port is the tinc host configuration?

And why firewall blocked this? How to adjust to  make it more friendly?
-- 
Sent from iPhone
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.tinc-vpn.org/pipermail/tinc/attachments/20170718/710b9b39/attachment.html>