19.7. Internet Sharing

19.6. Multihoming

Speaking of different ways to get online, Mac OS X offers one of the coolest features known to Internet-loving humanity: multihoming . That's the ability to maintain multiple simultaneous network connections open ”Ethernet, AirPort, dial-up, even FireWire. If one of your programs needs Internet access, and the first method isn't hooked up, the Mac switches to the next available connection ”automatically.

This feature is ideal for laptops. When you open your Web browser, your laptop might first check to see if it's at the office, plugged into a cable modem via the Ethernet ”the fastest possible connection. If not, it automatically looks for an AirPort network. Finally, if it draws a blank there, the laptop reluctantly dials the modem. It may not be the fastest Internet connection, but it's all you've got at the moment.

In short, for each location you create, you can specify which network connections the Mac should look for, and in which order. You can even turn off some connections entirely. For example, if you have a desktop Mac that's always connected to a cable modem, you may never want your Mac to dial using its built-in modem. In that case, you could turn off the modem entirely.

Here's how to go about using this multihoming feature:

1. Open System Preferences. Click the Network icon .

   The Network Status screen (Figure 19-1) brings home the point of multihoming: You can have more than one network connection operating at once.

   Make sure the appropriate location is selected in the Location pop-up menu.

2. From the Show pop-up menu, choose Network Port Configurations .

   Now you see the display shown in Figure 19-6. It lists all the different ways your Mac knows how to get online, or onto an office network.

   

   Figure 19-6. The key to multihoming is sliding the network connection methods ' names up or down (and turning off the ones you don't intend to use in this location). You can also rename the different configurations by double-clicking them.

   
   

3. Drag the items up and down in the list into priority order .

   If you have a wired broadband connection, for example, you might want to drag Built-in Ethernet to the top of the list, since that's almost always the fastest way to get online.

   At this point, you can also turn off any connections you don't want your Mac to use when it's in this location ”the internal modem, for example.

4. Click Apply Now .

   Your Mac will now be able to switch connections even in real time, during a single Internet session. If lightning takes out your cable modem in the middle of your Web surfing, your Mac will seamlessly switch to your AirPort network, for example, to keep your session alive .