Gateway WAN interface has no IP, private address

I am trying to set up a gateway on a new install of OS X 10.6. I have the WAN connected to the first ethernet port on my XSERVE which connects to my cable modem. The second ethernet port connects to a DIR655 wireless router (I have it set up to only fuction as a switch and wireless, no DHCP or firewall). The internal network us working fine, and the XSERVE is routing and doing DHCP. However, the WAN connection cannot get an IP address from the modem... It has an automatic private address. The connection is working, I tried it directly into a computer. But it will not work on the xserve. I have powered off all equipment and still no luck. I have tried both stright thru and crossover ethernet cables. Please help!