http://www.cyberciti.biz/faq/rhel-centos-fedoracore-linux-network-card-configuration/

Howto Red hat enterprise Linux 5 configure the network card

by nixCraft on April 10, 2007 · 87 comments· last updated at October 21, 2007

Q. I’ve installed Red Hat enterprise Linux 5 and now added one more LAN card (NIC). How do I configure the network card from the command line? I can see 2nd my network card detected while booting the IBM server.
A. Red hat Linux provides following tools to make changes to Network configuration such as add new card, assign IP address, change DNS server etc.
[a] GUI tool (X Windows required) - system-config-network
[b] Command line text based GUI tool (No X Windows required) - system-config-network
[c] Edit configuration files stored in /etc/sysconfig/network-scripts/ directory.
Following instructions are compatible with
(1) Cent OS Linux
(2) Fedora Core Linux
(3) Red Hat Enterprise Linux (RHEL) 3/4/5
Note: If you are using Debian or Ubuntu Linux, please see this configuration howto.

Method # 1: GUI tool system-config-network

Type the following command at shell prompt (open x terminal):
$ system-config-network &

You will see Window as above. Now select your Ethernet card (eth0 or eth1) and click on Edit button. You can now setup IP address, netmask, default gateway and other properties.

You can obtain IP address using DHCP or setup manually. Once IP address assigned, click on Ok button to save the changes. You can activate card by clicking on Activate button.

Method # 2: Command line tool system-config-network-tui

If you don’t have X windows GUI installed type the following command at shell prompt:
# system-config-network-tui &

(click to enlarge image)
You will see text based GUI as above. Select your Ethernet card (eth0 or eth1) and hit [Enter] or [F12] special key.

(click to enlarge image)
You can obtain IP address using DHCP or setup manually. Once IP address assigned, click on Ok button to save the changes

Method #3: Edit configuration files stored in /etc/sysconfig/network-scripts/

You can configure network card by editing text files stored in /etc/sysconfig/network-scripts/ directory. First change directory to /etc/sysconfig/network-scripts/:
# cd /etc/sysconfig/network-scripts/
You need to edit / create files as follows:

• /etc/sysconfig/network-scripts/ifcfg-eth0 : First Ethernet card configuration file
• /etc/sysconfig/network-scripts/ifcfg-eth1 : Second Ethernet card configuration file

To edit/create first NIC file, type command:
# vi ifcfg-eth0
Append/modify as follows:

# Intel Corporation 82573E Gigabit Ethernet Controller (Copper)
DEVICE=eth0
BOOTPROTO=static
DHCPCLASS=
HWADDR=00:30:48:56:A6:2E
IPADDR=10.10.29.66
NETMASK=255.255.255.192
ONBOOT=yes

Save and close the file. Define default gateway (router IP) and hostname in /etc/sysconfig//network file:
# vi /etc/sysconfig/network
Append/modify configuration as follows:
NETWORKING=yes
HOSTNAME=www1.nixcraft.in
GATEWAY=10.10.29.65

Save and close the file. Restart networking:
# /etc/init.d/network restart
Make sure you have correct DNS server defined in /etc/resolv.conf file:
# vi /etc/resolv.conf
Setup DNS Server as follows:
nameserver 10.0.80.11
nameserver 10.0.80.12
nameserver 202.67.222.222
Save and close the file. Now you can ping the gateway/other hosts:
$ ping 10.0.80.12
Output:

PING 10.0.80.12 (10.0.80.12) 56(84) bytes of data.
64 bytes from 10.0.80.12: icmp_seq=1 ttl=251 time=0.972 ms
64 bytes from 10.0.80.12: icmp_seq=2 ttl=251 time=1.11 ms

You can also check for Internet connectivity with nslookup or host command:
$ nslookup cyberciti.biz
Output:

Server:         10.0.80.11
Address:        10.0.80.11#53
Non-authoritative answer:
Name:   cyberciti.biz
Address: 75.126.43.232

You can also use host command:
$ host nixcraft.in
Output:

nixcraft.in has address 75.126.43.232
nixcraft.in mail is handled by 10 mail.nixcraft.in.