[Freeswitch-users] NAT type unknown, ExtIP empty, and ACK timeout

Hi, I am running FS behind a nat, however the nat does not seem to work and nat_map status shows: NAT type unknown, ExtIP empty. My call to the server on external context always get disconnected in about 30 seconds. Siptrace indicate a ACK timeout as the reason. I am using a TP-Link router and already set the server as DMZ host. Can anyone help? Thanks