No audio for one way internal calls

Hi everyone !

The problem is that I have full audio when I CALL from device 1 (IP Phone Grandstream) to device 2 (Zoiper on my computer) but when I call from device 2 (Zoiper) to device 1 (IP Phone) I have totally no audio.

I’m using FreePBX 15, the 2 devices are in a local network and my physical FreePBX server is in a DMZ (my factory wanted to do that for better security because I’m student and not a pro…), the 2 extensions are with Chan_SIP in 5060 port, I put NAT to “yes” with my public static address that I know. In SIP settings I put my 2 local networks : the DMZ network and the internal network with the 2 devices. For register I use the private ip address of my server in DMZ.

I forwarded ports UDP 5060 and 10.000 to 20.000 for audio

I tested with a VM FreePBX on my internal network, the audio is good for both call ways with Zoiper and my IP Phone

I did some research and I found nothing for that, it’s pretty weird that there is audio just for a one way CALL, I can provide more informations such as logs or something else if needed

Thank you so much in advance !


The problem was due to the big Firewall of my DMZ, it didn’t forward the 10.000 to 20.000 ports for my internal network, now I have audio both sides call, hope it helps !

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