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Strange problems on port forwarding [syn sent]

Posted: Tue Mar 27, 2018 12:33 pm
by pronet
Good morning guys,
we are connecting some of our customers via some OVPN-Tunnels (about 250 clients).

Every client has its own local subnet with a webserver serving some data over the VPN-Tunnel (see network diagram).

The routing is done via OSPF (NBMA) = this is up and running!
External access to the the specified ports, is natted over the VPN-Tunnels to the right destination = this is up and running, but not always..

Sometimes the connection between the endpoints is established like in the follwing screenshot and data is traveling without problems:
Established.PNG
But sometimes the connection attemp is just hanging in a "TCP syn sent"-state (screenshot firewall: fw0):
Syn Sent.PNG
The same "TCP syn sent"-state is on the other end of the tunnel (screenshot firewall: fw1):
Syn Sent 2.PNG

Could this be a bug, or is this behaviour "normal" when tunneling data over OVPN-TCP?
I'm going crazy.. :) :D

Thanks in advance!

Re: Strange problems on port forwarding [syn sent]

Posted: Mon Apr 02, 2018 4:04 pm
by Anumrak
What MTU do you have on tunnel interfaces?