Configuring Static Network Settings (IP address, netmask, and gateway) in Ubuntu Linux

Static IP Address Assignment
To configure your system to use a static IP address assignment, add the static method to the inet address  statement for the appropriate interface in the file /etc/network/interfaces. The example below assumes you are configuring your first Ethernet interface identified as eth0. Change the address, netmask, and gateway values to meet the requirements of your network.

auto eth0
iface eth0 inet static
address 192.168.1.2
netmask 255.255.255.0
gateway 192.168.1.1

By adding an interface configuration as shown above, you can manually enable the interface through the ifup command: sudo ifup eth0

To manually disable the interface, you can use the ifdown command: sudo ifdown eth0

DNS Client Configuration
To configure your system to use DNS for name resolution, add the IP addresses of the DNS servers that are appropriate for your network in the file /etc/resolv.conf. You can also add an optional DNS suffix search-lists to match your network domain names.

Below is an example of a typical configuration of /etc/resolv.conf for a server on the domain "example.com" and using two Google public DNS servers.

search example.com
nameserver 8.8.8.8
nameserver 8.8.4.4

If you have multiple domains you wish to search, your configuration might look like the following.

search example.com sales.example.com dev.example.com
nameserver 8.8.8.8
nameserver 8.8.4.4