I am trying to set up an SBox-100 (Safe@Home 5.0.94s firmware) to work with a Netopia 3346N-002 ADSL modem's IP Passthrough function. Netopia indicates that you have to enter the MAC address of the computer (would be the SBox's WAN MAC address in this case) that you want your public IP address forwarded to. The Netopia is set to assign the public IP address via DHCP.

- If I enter the SBox's WAN MAC address in the Netopia configuration, there is no connection- the SBox "PWR/SEC" light flashes constantly.

- If I enter the Ethernet port MAC address of my computer into the Netopia configuration and connect the Netopia directly to the computer, the computer gets my public IP address assigned to it- this indicates that the IP Passthrough is working in the Netopia.

-If I clone the computer's MAC address to the SBox's WAN port and enter that MAC address into the Netopia configuration, there is still no communication between the Netopia and the SBox.

-If I replace the SBox with a WatchGuard FireBox SOHO 6 tc firewall and insert its WAN MAC address into the Netopia configuration, the WatchGuard gets the public IP address assigned to it.

-Cloning the WatchGuard's WAN MAC address into the SBox and entering the WatchGuard WAN MAC address into the Netopia configuration will not enable the Netopia to talk to the SBox.

-I have tried both the Cable Modem and LAN options for the SBox's WAN port- no difference.

-Changing the SBox security level has no effect on the problem.

-Removing power from both the Netopia and the SBox and then re-applying power (first the Netopia and then the S-Box) does not solve the problem.

-If I disable the IP Passthrough function of the Netopia, it will assign a private IP address to the SBox and the two units will happily communicate with each other. However, then I have double-NAT, which is what I want to avoid with the IP Passthrough.

Any ideas as to why the IP Passthrough will work for my computer and for the WatchGuard, but not for the SBox?

Thank you in advance for your responses.