CertiGuide to A+ (A+ 4 Real)  9  Chapter 5: The Linux Operating System       9  Networking with Linux

ifconfig - Configure a Network Interface 1 Chapter 6: The Graphical Interface of the LINUX OS

The route command will show you the existing routing table and more importantly, if your system operates through a gateway, the default gateway can be setup using this command. Entering the basic command, route, will show the existing routing table. For example:

Destination Gateway Genmask Flags Metric Ref Use Iface

192.168.1.0 * 255.255.255.0 U 0 0 0 eth0

127.0.0.0 * 255.0.0.0 U 0 0 0 lo

default 192.168.1.1 0.0.0.0 UG 0 0 0 eth0

This shows for this machine that a default gateway exists at IP address 192.168.1.1. The default gateway if not set can be added using the route command in the following format:

route add default gw gateway_ip

Where gateway_ip would be the IP address of the gateway/router for the subnet.

Setting up interfaces in this manner will last until next reboot. Each distribution has a file in the /etc directory where this configuration information is stored. For example, RedHat and Mandrake store this information and more somewhere in the directory /etc/sysconfig. The location that RedHat uses is the file /etc/sysconfig/network-scripts/ifcfg-eth0. The location of the file for your system could be found using the command:

grep -r „IPADDR’ /etc/*

This search should be done with super user privileges. The file and a line in the file that the string IPADDR matches would be shown. This should contain the assigned IP address.

Finallly the file /etc/resolv.conf must have the apprpprate DNS nameserver's ip address added so that DNS lookups will occur. Add a line like this:

namserver DNS_IP

where DNS_IP is the actual ip address of the DNS server.

ifconfig - Configure a Network Interface 1 Chapter 6: The Graphical Interface of the LINUX OS