Question:

3CX is installed in the cloud server, and VOPTech FXO gateway is installed in the local network, after FXO gateway registers to 3CX in gateway mode, 3CX extensions can receive the inbound call from FXO gateway, but 3CX extensions cannot call out through the FXO gateway. When 3CX extensions call out, the FXO gateway does not receive any call logs (Logs->Call message), it indicates that the call does not reach the gateway. In order to check if firewall or router in gateway side stops the sip calls, we open the sip port and rtp port of gateway in the firewall or router, but the gateway still can not receive any call logs.

Solution:

When 3CX extensions call out, we make a capture in 3CX server, and find that 3CX keeps sending the invite requests to the public IP of gateway, but 3CX does not receive any responses from gateway. After that, we make a capture in 3CX to check the registration port of gateway, and find that the registration port is not the local sip port of gateway, the local sip port is 5060, but the registration port is 1025:

In the sip trunk of 3CX, after we change the port 5060 as 1025, 3CX extensions can call out through the FXO gateway.

As usual, gateway uses 5060 port to register, after the gateway goes through the firewall or router in gateway side, the registration port is changed as 1025. Then we find that the port 5060 is used by the other devices in the port forwarding of firewall, so we change the local port as any other port in the FXO gateway, the registration port which 3CX receives from gateway will be the local port of gateway.

Suggestions:

In order to make sure the registration port which 3CX receives from gateway is same as the local port of gateway, and also ensure the security of gateway, please refer to the below suggestions:

1.In the gateway, set the option (Increments of port number) as No backup.

2.Change the local port as any other non-5060 ports:

3.Set the route table, just route the call from the 3CX server to the FXO:

4.In the firewall of gateway side, set the firewall rule and make sure firewall just allows the data from 3CX server to go to the gateway.

5.In the firewall of gateway side, please make sure the local port of gateway is not used by the other devices in the port forwarding.