Network Configuration

If Ethernet card was present during installation, the installation program will allow you to configure the device.But this post deals with modification of  configuration after installation. Even if you don’t need to modify the network settings, you can use this information to verify if the settings are correct.

NOTE:-
Because some servers do not have graphical desktops installed, we have consider the network configuration from the command line by modifying configuration files. If you have a graphical desktop and want to use a graphical application, go to the System menu on the top panel and select Administration, Network.





Network Configuration Files
The following configuration files exist for network configuration:

File	Use
. /etc/modprobe.conf file	This assigns a kernel module to each network device.
. /etc/sysconfig/network file	It Sets the hostname and check whether the networking is enabled.IPv6 is enabled or disabled.
. /etc/hosts files	Lists hosts and their IP addresses for hostnames that can’t be resolved by the DNS servers
. /etc/resolv.conf file	Sets the DNS servers (using their IP addresses)and the search domain. The values of the DNS servers are often tend to be added when the network is activated because the data can be provided by DHCP or a similar service.
. /etc/sysconfig/network-scripts/ directory	Contains scripts to start and stop a network device and a specialized configuration file for each device.
. /etc/rc.d/init.d/network file	Initialization script that starts and stops the network.

 CAUTION:-
If the Graphical Network Configuration Tool from the Administration, Network menu item of the System menu has ever been run on the system, an /etc/sysconfig/ networking/ directory will exist. The files in this directory are only used by the graphical tool and are not by any of the network scripts. If changes are made to these files, they will not be applied to the actual network configuration files used.

Some of the network configuration files such as the ifup and ifdown scripts in /etc/ sysconfig/network-scripts/ does not need to be modified in most cases and should not be modified unless absolutely necessary. We are considering the network configuration files that may have to be modified to change the network settings and how to enable the changes.

Case-1 shows an example of a /etc/modprobe.conf file. The first line assigns the e100 kernel module to the eth0 network device. If the network card is supported, the module is automatically configured during installation or by Kudzu the first time the system is booted with the new card.

CASE-1 
/etc/modprobe.conf
alias eth0 e100
alias scsi_hostadapter sata_sil
alias scsi_hostadapter1 ata_piix


The /etc/sysconfig/network file usually contains the content shown in CASE-2. If the NETWORKING option is set to yes, the networking subsystem is enabled but not necessarily started at boot time. The value of the HOSTNAME option is the hostname for the system. If it is not set, the default hostname is localhost. Refer to the file /usr/share/doc/ initscripts-/sysconfig.txt for additional options for this file.

CASE-2 
/etc/sysconfig/network
NETWORKING=yes
HOSTNAME=smallville