Running Mac OS X Tiger

Configuring IP Addresses

When IP was first used, every computer on a network had to be hand-configured with a static IP address and a netmask address before it could communicate with other machines. While it’s nice to have a static IP address, it also meant that it was possible to run out of IP addresses assigned to a domain. This often forced sysadmins to restrict certain users from access to network services (file sharing, printing, even the Internet) by not assigning an IP address to a certain class of machines or users, with dedicated “network” computers in each group from which the network could be accessed. As you can imagine, that was a real pain.

Fortunately for today’s users, most networks provide Dynamic Host Configuration Protocol (DHCP ) services. These services allow computers to be configured automatically with an IP address and netmask for that particular network. DHCP also helps conserve IP addresses by letting a potentially large number of computers share a smaller number of active IP addresses. DHCP services are provided by a separate server on the network or can be built into the hardware, known as a gateway router, providing access to the Internet via an ISP.

When you plug your computer into a DHCP-enabled network, your machine sends out a low-level request to the DHCP server for configuration information. The DHCP server responds by sending the IP address, netmask, router, and DNS information that the computer needs to connect to the network. Your computer uses ...