The WAN Interface is an effective connection to permit point to point networking within a wide area network. This protocol is usually utilized for DSL and not for cable modems. Actually the part for configuring PPPoE in the Control Center is below the DSL tab. Ensure your network card in the Control Center: Menu- Control Center- Internet and Network- Network: make certain connection is enabled, after that check this part. Menu- Control Center- Internet and Network- Network Connections- DSL: make certain the information is accurate. Generally on shared connections the elegant method to set it up is to facilitate PPPoE in the router and have the router allocate addresses via DHCP. How much people split this cable modem connection? Maybe your ISP can program their router or switch to distribute DHCP, except they require divide IP's for everybody for billing. Your condition is strange, if not anything over worked you can attempt running these commands in a terminal and place the output here for additional investigation, however I cannot assure anything as I am not very recognizable with PPPoE in Linux.
Lastly sprint this to verify for errors
As well, observe if you can discover from your ISP what type of modem you had earlier than this cable modem.