We are running a Cisco RV325 and using an AT&T SB67070 SIP Gateway with an SB67050 ATA. We were running into a problem where calls would come into our network but when we answered there would be no audio in either direction, but we could call out using the same phone. We were told by our service provider that the problem was that when the 200 ok was being sent out it was giving out a local IP to call back to instead of our external IP address.
We were able to fix this by utilizing the RV325s DMZ Host. (Setup > DMZ Host)
Here we entered the IP address of the SIP Gateway and that fixed our problem.
This was one of several things we did. Under Firewall > General we also
Enabled: Firewall, Remote Management, SPI ALG, and UPnP
Disabled: SPI, Dos, Block Wan Request, Multicast Pass Through, HTTPS, SSH, and Remote SSH.
Under System Management we also disabled LLDP and Discovery-Bonjour.
We did all of these things based off the advice of different service providers and all of them together seem to work. I am not sure whether or not some of these settings can be changed.
