3CX Client puzzler

[mgb2]

I've got a strange situation I'm trying to figure out.
Network setup:

Internet------FW------3CX Server-------FW1----LAN1 (IP Phones)
|
----FW2----LAN2 (Mobile devices)

I'm using split DNS so I can always use the companyname.3cx.us hostname. The actual IP of the server is 10.200.1.28.

Mobile devices with the 3CX client installed use wifi on LAN2, passing through FW2, which does NATing to it's 10.200.0.x address (note that this network is a /16, so this interface and the server are on the same subnet).

When a new extension is created, the system provisions a 3CX Client phone, and preselects 10.200.1.28 as the network interface for registering and provisioning. When the client is then provisioned, it thinks it should use 10.200.1.28 for the local IP, and companyname.3cx.us as the external IP. When using the carrier network or another external wifi network, everything works. Internally (on LAN2), however, it appears to signal correctly, but no audio passes in either direction.

Now, if I look at the device provisioning in the management console, I can change the interface to companyname.3cx.us, reprovision within the client, and everything works. This has me confused, as the FQDN correctly resolves the IP address.

So, first, can anyone explain the behavior I'm seeing? Second, if there's no good explanation or solution, is there a way to make sure 3CX uses the FQDN for the initial configuration, so it doesn't have to be manually changed?

 

[YiannisH_3CX]

Hello @mgb2

What i think is happening when you switch the internal link to the FQDN is that the client connects externally using the public IP and that's why it works. The reason why it does not work with the local IP could be a miss configuration on the firewall that is causing the audio to be blocked. Have you tried the same scenario on LAN1 to see if the issue is the same? You could use a 3CX client for windows to try and replicate.

Please note that the client will always display the local IP for the in office connection as it is detected when the client connects to the PBX even if the system is configured with split DNS