Using a Mac Running OS X to Share an Internet AccountMac OS X includes a built-in DHCP server you can use to share a single Internet connection with other devices on your local network. And if the Macintosh on which you configure the DHCP server includes an AirPort card, you can also provide a wireless AirPort network without the use of an AirPort base station. NOTE The function of the DHCP server is to provide and manage IP addresses to devices on the network. The DHCP server doesn't actually provide the Internet access itself; that comes from the connection method you use (such as a cable modem). The DHCP server manages the traffic between the Internet connection and the other devices on the network. One advantage of this approach is that you don't need to add dedicated Internet sharing hardware (such as a sharing hub or an AirPort base station) to your network. A standard Ethernet hub enables you to share an Internet account over an Ethernet network, and an AirPort card enables you to share an account over a wireless AirPort network. Another advantage is that it doesn't cost anything to share an account (assuming that you already have the connection hardware, such as for an Ethernet network). NOTE You can use Mac OS X's built-in firewall to protect the DHCP machine from attacks from the Internet (and because it sits between the Internet and the other devices on your network, it protects those devices as well).
To learn how to configure the Mac OS X firewall, p. 911. This approach does have one significant disadvantage and one minor drawback, however. The significant disadvantage is that the Mac providing DHCP services must always be running for the machines that share its account to be capable of accessing the Internet. If the DHCP machine develops a problem, no device on the network can access the Internet. Similarly, if the machine from which the account is shared goes to sleep, the connection is lost by all the computers on the network. The less significant issue is that the DHCP services do require some processing power. These services will most likely not result in any noticeable performance decrease, but if your machine already runs at its limits, asking it to provide these services might slightly slow down other tasks. NOTE DHCP servers are not platform specific. For example, if you have a DHCP server running on a Macintosh, you can connect a Windows computer to the network and use the same DHCP server to share the Internet account with it. Or, you can install a DHCP server on a Windows machine and use it to share the account with Macs on the network. Configuring a Mac to provide DHCP services to a network requires the following general steps:
Connecting the DHCP Mac to the InternetIt goes without saying (but I will say it anyway) that to use a Mac to share an Internet account, that Mac must be connected to the Internet. The method you use to connect to the Internet doesn't matter. You'll get the best results if you use a broadband connection, such as a cable DSL modem, but you can also share a dial-up connection if you want (don't expect speedy operation, though).
To learn how to connect a Mac to the Internet, p. 263. Installing the DHCP Mac on a NetworkThe next step is to install the DHCP Mac on the network with which you are going to share the Internet connection. You can build a wired network using Ethernet, or you can install an AirPort card to connect the Mac to other AirPort-equipped Macs (you can share an account with other machines using both networking methods at the same time).
To learn how to install, configure, and use an AirPort network, p. 297.
To learn about Ethernet, p. 705.
To learn about Ethernet hubs, p. 808.
To learn how to build and manage a network, p. 821. Configuring the DHCP Mac to Share an AccountAfter you have configured the Mac for Internet access and connected it to other computers (with or without wires), you need to configure the Internet sharing services on it. The three possibilities when you configure Internet sharing on your Mac are as follows:
NOTE AirPort base stations, except the original version, include an Ethernet port you can use to connect the base station to an Ethernet network. When you do this, the base station can also share a connection with machines connected to the Ethernet network. In that case, you don't need to use a Mac to share a connection. When you configure Internet sharing on your Mac, it automatically determines which case is true for your machine and presents the appropriate options for you. To configure Internet sharing, use the following steps:
To learn how to install, configure, and use an AirPort network, p. 297.
To learn how to connect a Mac to the Internet, p. 263. TIP If you share an Internet account over AirPort, an upward pointing arrow is added to the center of the AirPort icon in the menu bar. This indicates that the connection is shared and that you can access the sharing controls from the menu. CAUTION If the machine sharing the connection goes to sleep, the Internet connection is lost on the network and no machine can access the Net. You should disable sleep using the Energy Saver pane of the System Preferences application when you use Internet Sharing. (In fact, when you start up sharing on a Mac that has sleep turned on, the Energy Saver button appears on the Internet pane so you can easily jump over and turn off sleep.)
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