One way audio from interconnected network

Hi Guys,

We are really stuck with this issue and would greatly appreciate some advice or insight of any kind. We recently swapped our Elastix PBX out with FreePBX. Where we had no issues.

We have our own voip network setup with over 100 extensions and there are no problems with audio with internal calls or external calls on the same subnet (

We also have a vpn from our office network that we make calls to extesnsion on the local network and there is no issues with audio. (

There is a cross connect from our network across to another office network that we do not manage, calls on this network can call each other with no audio issues, but if they try call the local network there is no audio. (

Firewalls have been thoroughly checked and temporarily disabled on the PBX and our Router. Fail2ban has also been checked.

The RTP config is all standard, using ports 10000 – 20000.

We have taken the voip phone from their network and tested in ours and all works ok there.
In a packet capture taken from our network (please see attached), we can see ICMP replies ‘Destination unreachable (port unreachable)’ however we can successfully ping the device from the same PBX to the other office network and get replies.

What is even stranger, we have another site setup with almost an identical configuration and same version of freePBX and do not experience the issues.

Freepbx version
PBX Firmware:12.7.4-1712-2.sng7
Asterisk 13.18.4

We are using PJSIP for the extesnions

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