Common (RHEL Red Hat, Ubuntu Server, and CentOS) Network Interface Configuration Locations and Basic Format

Red Hat Enterprise Linux Server release 5.3 (Tikanga)
File found in: /etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE=eth0
BOOTPROTO=static
IPADDR=%IP Address%
NETMASK=%Netmask%
GATEWAY=%Gateway%
ONBOOT=yes

Ubuntu Server 10.04 LTS
File found in: /etc/network/interfaces

auto eth0
iface eth0 inet static
address %IP Address%
netmask %Netmask%
gateway %Gateway%

CentOS release 5.8 (Final)
File found in: /etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE=eth0
BOOTPROTO=static
IPADDR=%IP Address%
NETMASK=%Netmask%
GATEWAY=%Gateway% 
ONBOOT=yes