Network Configuration on Ubuntu

Sample configuration file:

@sr2s17:~$ cat /etc/network/interfaces 

# This file describes the network interfaces available on your system

# and how to activate them. For more information, see interfaces(5).

# The loopback network interface

auto lo

iface lo inet loopback

# The primary network interface

auto eth0

iface eth0 inet dhcp

auto eth2

iface eth2 inet static

address 192.168.0.37

netmask 255.255.255.0

I use interface eth0 as the external network and eth2 as the internal network. 

After you install Ubuntu, the interfaces may not be up. Although you can use ethtool to detect if the interfaces are physically connected by cables, This approach is not accurate on Ubuntu (works on CentOS). 

For example, I know there are six interfaces on my server

eth0 and eth1 are on a broadcom network card, and eth2, 3, 4, 5 are on a Intel network card. 

I plugged the Ethernet cable to the eth2 interface, so I just need to write the script into /etc/network/interfaces, which help me to enable the eth2. Next, I run a $ /etc/init.d/networking restart