PPPoE Connections
If you are unable to connect to your ISP using PPPoE (Point to Point Protocol over Ethernet), make sure you entered the correct information in Network preferences.
To enter PPPoE settings:
1Choose Apple () > System Preferences.
2 Click Network.
3Click Add (+) at the bottom of the network connection services list, and choose PPPoE from the Interface
4Choose an interface for the PPPoE service from the Ethernet
5Click Create.
6Enter the information you received from your service provider, such as the account name, password, and PPPoE service name (if your service provider requires it).
7Click Apply to make the settings active.
Network Connections
Make sure the Ethernet cable is plugged into your iMac and into the network. Check the cables and power supplies to your Ethernet hubs and routers.
If you have two or more computers sharing an Internet connection, be sure that your network is set up properly. You need to know whether your ISP provides only one IP address or multiple IP addresses, one for each computer.