OS X Yosemite: The Missing Manual

Internet Sharing

If you have cable modem or DSL service, you’re a very lucky individual. You get terrific Internet speed and an always-on connection. Too bad only one computer in your household or office can enjoy these luxuries.

It doesn’t have to be that way. You can spread the joy of high-speed Internet to every Mac (and PC) on your network in either of two ways:

• Buy a router. A router is a little box, costing about $50, that connects directly to the cable modem or DSL box. In most cases, it has multiple Internet jacks so you can plug in several Macs, PCs, and/or wireless base stations. As a bonus, a router provides excellent security, serving as a firewall to keep out unsolicited visits from hackers on the Internet.

• Use Internet Sharing. OS X’s Internet Sharing feature is the software version of a router: It distributes a single Internet signal to every computer on the network. But unlike a router, it’s free. You just fire it up on the one Mac that’s connected directly to the Internet—the gateway computer.

  But there’s a downside: If the gateway Mac is turned off or asleep, then the other machines can’t get online.

Most people use Internet Sharing to share a broadband connection like a cable modem or DSL. But there are other times when it comes in handy. If you have a cellular modem, for example, you might want to share its signal via WiFi so the kids in the backseat can get online with their iPod Touches.

The only requirement: The Internet-connected Mac must have some other kind of ...