I'm having a problem with a NAT scenario, I have some pcs (192.168.10.102 and 192.168.10.103) using verto behind a NAT calling to a LAN FS (192.168.10.143).

I added a gateway and the callout is working good enough, but the calls between extensions I am not getting audio, I just get the "No audio stun for a long time!".

I set in many ways the following: 

 <param name="ext-rtp-ip" value="192.168.30.143"/>                            
 <param name="ext-sip-ip" value="auto"/>   

I tried auto, auto-nat, $${external_rtp_ip} and $${external_sip_ip} respectively, and that one I just added with no luck. 

What can be the problem with this?

Thanks

Jose