Mac OS X: The Missing Manual, Second Edition

Internet Sharing

If you have cable modem or DSL service, you’re a very lucky individual. Not only do you benefit from spectacular speed when surfing the Web or processing email, but your connection is on full-time. You never have to wait for some modem to dial (screeching all the way), and wait again for it to disconnect. It’s just too bad that only one computer in your household or office can enjoy these luxuries.

Internet Sharing as a Bridge

Ordinarily, only one Mac has Internet Sharing turned on: the one that’s connected directly to the Internet.

There are, however, times when you might want another machine “downstream” to have it turned on, too—and that’s when you want to bridge two networks.

Consider the setup illustrated here, where there are really two different networks: one that uses AirPort, and another connected to an Ethernet hub.

If you play your cards right, you can actually set things up so that all of these Macs can get online simultaneously, using a single Internet connection.

Set up the gateway Mac so that it’s an AirPort base station, exactly as described on these pages.

Start setting up the bridge Mac the way you’d set up the other AirPort Macs—with AirPort selected as the primary connection method, and “Using DHCP” turned on in the Network panel.

Then visit the bridge Mac’s Sharing panel. Turn on Internet Sharing here, too, but this time select “Share the connection with ...