Apple MACBOOK - Manual (Page 121)

Appendix C Connecting to the Internet 121
Network Connections
If you have two or more computers attempting to share an Internet connection, make
sure that your network is set up properly. You need to know if your ISP provides only
one IP address or if it provides multiple IP addresses, one for each computer.
If only one IP address is used, 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 Extreme Base Station can be used to
share one IP address among multiple computers. For information about using the
AirPort Extreme Base Station, check the onscreen help or visit the Apple AirPort
website at www.apple.com/airportextreme.
If you can’t resolve the issue using these steps, contact your ISP.