You can configure ETH WAN Fast Ethernet ports as a WAN port using PPPoE (PPP over Ethernet). PPPoE offers dialup style authentication and accounting and allows subscribers to dynamically select their ISP.

PPPoE is a client-server protocol used for carrying PPP-encapsulated data over Ethernet frames. A PPPoE client can establish a tunnel that carries PPP frames between a dialing host (the Branch Gateway) and an access concentrator. This enables the use of PPP authentication protocols (CHAP and PAP). Unlike other tunneling protocols such as L2TP and PPTP, PPPoE works directly over Ethernet rather than IP.

A typical broadband access network is based on ADSL modems configured as transparent Ethernet bridges. ADSL modems use ATM protocol, and the transparent bridging is done to a well known ATM VC. On the other side of the telephone line is a device called a DSLAM. The DSLAM terminates the ADSL physical layer, collects the ATM cells from the various ADSL subscribers, and places them on the SP ATM infrastructure. The Ethernet frames from the customer’s host device can reach one or more access concentrators, which are the remote access servers.