A mate of mine has a super old Cisco DPC3008 and Netcomm Wireless NF5. The Netcomm has died and he's bought a new wifi router, plugged it in but it doesn't seem to be getting a DHCP address from the cable modem.

Is DHCP the correct protocol, and it's not something wacky like PPPoE? Is there anything else I need to tell him to do to get it working? Do the cable modems still cache the MAC of the device plugged into them?