i did so, and also on the DMZ tab i have this option called 
 
	External Interface: 
	   - VLAN 100 - PPP - WAN Ethernet (100.108.77.19)   
	   - VLAN 835 - PPP - WAN Ethernet (Static IPv4 Address not configured)   
	   - PPP - WAN Ethernet (Static IPv4 Address not configured)   
	   - PPP - PTM (Static IPv4 Address not configured)   
	   - VLAN 835 - PPP - PTM (Static IPv4 Address not configured)   
	   - VLAN 100 - PPP - PTM (Static IPv4 Address not configured)   
	   - PPP - Ethernet over ATM, 8/35 (Static IPv4 Address not configured)   
	   - PPP - Ethernet over ATM, 8/36 (Static IPv4 Address not configured)   
	 
	what should I select? 
	and also is there a site or way I can test if there is this double NAT problem? 
	 
	Thank you so much for your time.