Chapter 8. Network Interfaces

Under Red Hat Linux, all network communications occur between configured software interfaces and physical networking devices connected to the system.

The configuration files for network interfaces, and the scripts to activate and deactivate them, are located in the /etc/sysconfig/network-scripts/ directory. Although the number and type of interface files can differ from system to system, there are three categories of files that exist in this directory:

Interface configuration files
Interface control scripts
Network function files

The files in each of these categories work together to enable various network devices under Red Hat Linux.

This chapter will explore the relationship between these files and how they are used.

8.1. Network Configuration Files

Before delving into the interface configuration files, let us first itemize the primary configuration files used in network configuration. Understanding the role these files play in setting up the network stack can be helpful when customizing a Red Hat Linux system.

The primary network configuration files are as follows:

/etc/hosts — The main purpose of this file is to resolve hostnames that cannot be resolved any other way. It can also be used to resolve hostnames on small networks with no DNS server. Regardless of the type of network the computer is on, this file should contain a line specifying the IP address of the loopback device (127.0.0.1) as localhost.localdomain. For more information, see the hosts man page.
/etc/resolv.conf — This file specifies the IP addresses of DNS servers and the search domain. Unless configured to do otherwise, the network initialization scripts populate this file. For more information on this file, see the resolv.conf man page.
/etc/sysconfig/network — Specifies routing and host information for all network interfaces. For more information on this file and the directives it accepts, see Section 4.1.23 /etc/sysconfig/network.
/etc/sysconfig/network-scripts/ifcfg-<interface-name> — For each network interface on a Red Hat Linux system, there is a corresponding interface configuration script. Each of these files provide information specific to a particular network interface. See Section 8.2 Interface Configuration Files for more information on this type of file and the directives it accepts.

	Caution
	The `/etc/sysconfig/networking/` directory is used by the Network Administration Tool (`redhat-config-network`) and its contents should not be edited manually. For more information about configuring network interfaces using the Network Administration Tool, see the chapter called Network Configuration in the Red Hat Linux Customization Guide.