Apple Mac mini (Intel-based; Mid 2007) - Manual (Page 38)

38 Chapter 3 Problem, Meet Solution
Network Connections
Make sure the Ethernet cable is plugged into your Mac mini and into the network.
Check the cables and power supplies to your Ethernet hubs and routers.
If you have two or more computers attempting to share 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.