ubuntu change IP address

open the /etc/network/interfaces file.

sudo vi /etc/network/interfaces

If you are using DHCP for your primary network card which is usually eth0, you will see the following lines

auto eth0
iface eth0 inet dhcp

As you can see, it’s using DHCP right now. We are going to change dhcp to static, and then there are a number of options that should add and here is the example and you can change these settings according to your network settings.

auto eth0
iface eth0 inet static
address 192.168.1.100
netmask 255.255.255.0
network 192.168.1.0
broadcast 192.168.1.255
gateway 192.168.1.1

Change DNS server address

sudo vi /etc/resolv.conf
name server 203.192.133.3

Restart the neworking service using the following command

sudo /etc/init.d/networking restart

This is from http://www.ubuntugeek.com/change-ubuntu-system-from-dhcp-to-a-static-ip-address.html