ONE WAY audio problem!

I am having a ONE WAY Audio problem

According to a Nerd Vittles tutorial I know that the sip_custom.conf file needs to be modified to avoid this kind of issues.
I did it but, as the problems persist, I am not sure if I did it OK.

My network is as follows:

My ISP give me an dinamic IP service so I use dynDNS (

I have a router (from my ISP, I can not get rid of it) configured
This router asign fixed ip to other router at
Asterisk is at and my PC with a softphone at

So, I have configured sip_custom.conf as follows:

but I have a One Way Audio problem. When I call any extension in my network It works ok. but when I dial to an extension loged in from outside I can hear but they don’t.

Any help?

Thanks in advance!

Best regards.

Make sure all of the appropriate ports are opened in the router as well as any firewall in the soft phone computer.


the first router opens a DMZ to and the second opens a DMZ to where Asterisk is.