.: Advanced Linux Networking :.

Although DHCP is a common method of configuration on many networks, it's not used universally. It's awkward to configure some systems (such as DHCP servers) via DHCP, and some networks simply lack DHCP servers. In these situations, you'll need to configure your computer's IP address manually. This section describes how to do this, starting with the tools to do the job a single time. The section entitled "Making Your Changes Permanent" describes how to configure your system to use your settings automatically whenever it reboots.

Configuring Network Interfaces
Loading a driver, as described earlier in this chapter, is the first step in making a network interface available. To use the interface, you must assign it an IP address and associated information, such as its network mask (also called the subnet mask or netmask). This job is handled by the ifconfig utility, which displays information on an interface or changes its configuration, depending upon how it's called.

Basic ifconfig Syntax and Use

The ifconfig utility's syntax is deceptively simple:

ifconfig [interface] [options]

The program behaves differently depending upon what parameters it's given. On a broad level, ifconfig can do several different things:

• If used without any parameters, ifconfig returns the status of all currently active network interfaces. Used in this way, ifconfig is a helpful diagnostic tool.
• If given a single interface name (such as eth0 or tr1), ifconfig returns information on that interface only. Again, this is a useful diagnostic tool.
• If fed options in addition to an interface name, ifconfig modifies the interface's operation according to the options' specifications. Most commonly, this means activating or deactivating an interface.