Wouldn't you know it I tested the last solution for 5 days then as soon as posted the accepted solution the problem came back. This question is the same as my previous question. Somehow or other after being connected for maybe 2 days asterisk finds the VoiP provider server unreachable, which is then fixed by power cycling the modem. The funny thing is the connection lasts longer with 1 router over the other. It happens with 3 routers. The same as before, when the connection is down I can ping the server using the server name not the ip address so I know it's resolving. I'm using the same NAT traversal method, namely specifying the externip= xx.xxx.xxx.xxx and localnet=192.168.0.0/255.255.255.0 in the config file. Once it goes down it does not come back.