Some cable and/or ADSL broadband providers authenicate using the MAC address of the modem or PC connecting to their network. The symptons of this might manifect themselves as being able to revert to the usual DSL connection by simply plugging the cable/ADSL modem back into my PC’s Ethernet port. That is, the system works fine until the router is inserted in between the DSL modem and the PC’s Ethernet port.
This is documented in the Netgear manuals and there are several pages on the technical support site about it. For example:
The manual also describes it in the WGT624 User manual (see pgs 3-10, 3-14, 7-4, 7-5 of the user manual). The MAC address of the original NIC MAC used when the connection to the ISP was first established needs to be spoofed or cloned (assuming the original connection probably did this by directly connecting the modem to the NIC in the PC).
MAC address cloning/spoofing (own experience).