33. Share Your Internet ConnectionBEFORE YOU BEGIN 27 Set Your Network Device Preference Order 30 Configure Networking Manually SEE ALSO 42 Create a Computer-to-Computer Network Suppose that you have only a single dial-up Internet connection but several computers that all have to be online at once. Normally, you can hook up only one computer at a time, through its own modem connection. But thanks to Internet Sharing, all the computers can be online at once, sharing the same connection. In this arrangement, one Mac is the central server that shares its connection with all the other computers. That Mac must have a working Internet connection such as the internal modem, Ethernet, or any other network port. That central Mac must also be hooked up to the other computers using an infrastructure such as AirPort or Ethernet. For instance, you might have a Mac with an Ethernet connection to a DSL modem, and an AirPort card with which it can share its connection with other AirPort-equipped computers; or your Mac might have a dial-up modem connection and be plugged in using Ethernet to a hub, with all the other computers likewise plugged into the same hub. 33. Share Your Internet Connection One network port on the central Mac is the active Internet connection, and the other port is the one you use to share the connection. All the other computers on the network need only be configured to use DHCP to obtain their TCP/IP information, and to use the same network device for their Internet connections that you're using to share it. For instance, if you are sharing your connection over AirPort, all the other computers must be using AirPort or compatible 802.11 devices as well. KEY TERMS 802.11 A protocol for wireless network connections. Apple's implementation is called AirPort; the same technology is also referred to in the rest of the industry as Wi-Fi. 802.11b, the earlier standard version, runs at 11 megabits per second; 802.11g, the more modern version, runs at up to 54 megabits per second and is called AirPort Extreme by Apple. AirPort is an optional add-on for most Macs. Network Address Translation (NAT) A scheme that allows computers on one side of the router to have different IP addresses in a special rangeusually 192.168.2.0 to 192.168.2.255 and for those computers to all share a single true IP address on the other side of the router. When your Mac has Internet Sharing enabled, the computer is actually acting as a DHCP server and NAT -enabled router. This means that external computers can't connect directly to any of the computers sharing their Internet connection from your Mac, because all they can see is the single real IP address that all the computers on your network are sharing. NOTE Computers sharing their Internet connections from your Mac don't all have to be Macs. Windows and Unix machines can all share your Internet connection; all they have to do is get their TCP/IP information through DHCP and use the network device you're using to share your Mac's Internet connection.
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