sudo vim /etc/network/interfaces

/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 p5p1
iface p5p1 inet static
address 192.168.0.99
netmask 255.255.255.0
network 192.168.0.0
broadcast 192.168.0.255
gateway 192.168.0.1

Since Ubuntu 12.04 the handling of resolv.conf changed. If you want to add your own nameserver address(es) then edit the file /etc/resolvconf/resolv.conf.d/head and add your nameserver there (e.g.: Google open dns)

sudo vim /etc/resolvconf/resolv.conf.d/head

/etc/resolvconf/resolv.conf.d/head

nameserver 8.8.8.8
nameserver 8.8.4.4

save the file and then run

sudo resolvconf -u

restart network settings

sudo /etc/init.d/networking restart