OpenVPN activity is triggering firewall drops

[serjmac]

Hi all, hope this is a simple question:

What kind of firewall warning could an incoming authentication OpenVPN UDP tun connection trigger? I'm having trouble with a working openvpn server, from a defined moment, the router's firewall DROPs any incoming packet from public IP client side to the LAN openvpn server. This effectively disables the possibility to access to the VPN until router is rebooted. After reboot, it works again until the traffic again is detected as undefined intrussion/firewall warning.

OpenVPN server is running in a linux device from within the LAN.

I have recently switched ISP router and I do know the problem is this routers firewall, because I see in its log that it is DROPing the packets. Never had this kind of problem with previously ISP routers. I dont know what kind of violation or suspicious activity OpenVPN generates so that the firewall is alerted and from then drops the traffic... openvpn is udp and tun.

I would be very gratefull if anyone knows how this firewall issue is being triggered by normal, standard, legit openVPN client->server traffic. I have been using windows and android as clients daily, in this linux server, for ages, without any problem at all. This modern router's firewall is driving me insane, don't know why it is being alerted

thank you

[TinCanTech]

Please see:
HOWTO: Request Help !

[serjmac]

OK Sorry .......