FreePBX - one way sound on external calls


I’ve been using FreePBX successfully for quite a while now, initially using a single server on a subnet of our main network.

With no changes to the network (I’m the network admin!)one day we couldn’t hear any audio on both outgoing and incoming calls. My assumptions were the router between the main network and the subnet.

By placing a FreePBX server on the main network and connecting an IAX2 trunk between them, we’ve now had 7 months of problem free running until…

Yesterday morning, again with no changes to any configurations, we’re back to one way sound again.

Config is

Phones: Cisco7940
Internal trunk: IAX2
External trunks: Sipgate SIP
ISP: Sharedband

The SIP provider and ISP deny any changes to their systems that would affect me. Now I’m stumped.

So my question is, where do I start to troubleshoot a connection that has worked for 7 months.

Any help in troubleshooting this much appreciated.

many thanks


If your config of FreePBX hasn’t changed at all (e.g. localnets, externip, etc) then have a look at your firewall to the Internet. I’d check to make sure this is not blocking any inbound traffic in your RTP range (check your /etc/asterisk/rtp.conf file for this range - usually 10000-20000). If the router is blocking these inbound for some reason you’ll get one way audio.

Agreed. It is either your NAT/Firewall or a problem with your provider.

This gave me sufficient ammunition to get the ISP to have a look at their systems and admit the problem was on their side.

An additional external IP address and host allocation has sorted out the problem.