Apple iMac (21.5 and 27-inch, Late 2009) - Manual (Page 52)

52 Chapter 4 Problem, Meet Solution
5 Enter the information you received from your service provider, such as the account
name, password, and PPPoE service name (if your service provider requires it).
6 Click 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.
If only one IP address is provided, then you must have a router capable of sharing the
connection, also known as network address translation (NAT) or “IP masquerading.”
For setup information, check the documentation provided with your router or ask
the person who set up your network. The AirPort base station can be used to share
one IP address among multiple computers. For information about using an AirPort
base station, check Mac Help or visit the AirPort Extreme website at
www.apple.com/support/airport.
If you can’t resolve the issue using these steps, contact your ISP or network
administrator.
Problems with AirPort Wireless Communication
If you have trouble using AirPort wireless communication:
 Make sure the computer or network you are trying to connect to is running and has a
wireless access point.