How to Configure Network System Preferences in Mac OS X Snow Leopard
Leave it to Mac OS X Snow Leopard to provide you with network configuration assistance when you first open the Network pane. (Whether you get this absolutely free offer of aid depends on whether you upgraded your Mac from a previous version of Mac OS X or whether you entered your network and Internet settings within the Snow Leopard Setup Assistant.)
If you don’t use Snow Leopard's assistance, you'll need to use Dynamic Host Configuration Protocol (DHCP) for automatic IP address assignment.
DHCP is a protocol that enables a computer to automatically get all the information it needs to communicate across a network. Before you can use DHCP, you have to add a DHCP server, which provides other computers on the network with their configuration settings. Here’s the good news: Most Internet connection-sharing hardware devices (and software-sharing implementations as well) provide a DHCP server as part of the price of admission. Most wired and wireless routers can provide DHCP services these days.
If you plan to use Internet connection sharing or you know that you have a DHCP server on your network, you can set up your Mac to automatically obtain the required IP address and information.
Open System Preferences from the Dock or the Apple menu and choose Network.
From the Network dialog that appears, click the Ethernet entry in the list on the left. Choose Using DHCP from the Configure IPv4 pop-up menu.Click Ethernet and choose Using DHCP.
Click the Apply Now button.
Mac OS X contacts the DHCP server to obtain an IP address, a subnet mask, a gateway router IP address, and a Domain Name System (DNS) address. (DNS servers convert a human-friendly address, like www.yahoo.com, to a computer-friendly IP address, like 126.96.36.199.)
A few seconds after clicking the Apply Now button, you should see the information come up, as provided by the DHCP server. This lets you know that the process worked and configuration is complete. You might also notice that the DNS Servers information is empty. Fear not: Mac OS X is really using DNS information provided by the DHCP server. Press Command+Q to quit System Preferences and save your settings.
If you ever make a network change that screws things up, such as entering the wrong subnet mask or an IP address that isn’t in the same range as others on your LAN, you can always click the Revert button to get back your old settings.
One DHCP server on a network is princely, but two or more DHCP servers on a single network will fight like alley cats and grind everything to a halt. Therefore, if you’re considering adding a DHCP server to an existing network, make doggone sure that you’re not treading on another server’s toes. (Ask that network administrator person.)