3CX V20 not connecting devices outside its subnet

[Anyingisye Maseta]

My 3CX V20 FQDN does not allow connection (service) from other subnets, it only register phones or allow web management when you are in same subnet. I have tried to run firewall check, disable windows firewall, disable antivirus, restart windows OS without success. I can access web management using IP Address from any subnet but that's not recommended, and it doesn't help softphones. The FQDN resolve without a problem, and I can even telnet to 3CX port number. How do I resolve this?

 

[VoIPTools]

My guess is that either (1) your DNS does not resolve to the correct IP address when attempting to connect from another network. Trying pinging from one of the subnets that does not successfully connect and confirm that it resolves to the correct address (either internal or external depending on where this subnet resides. (2), alternatively there may be something blocking or misrouting your requests. Again, try and ping the FQDN and see if you get a response back. Be aware, however, that one or more of your firewalls may be configured to not respond to ping (so it is not a perfect test).

If your FQDN should be resolving to an internal IP address, but is instead resolving to an external address, some routers do not handle hair-pinning well -- going out the external interface and then turning around and going back into the internal network.