edit your /etc/network/interfaces file to
auto eth0
iface eth0 inet static
address 192.168.0.50
netmask 255.255.255.0
network 192.168.0.0
broadcast 192.168.0.255
gateway 192.168.0.1
after that rebooting your network by excecuting the below command…
[root@localhost ~]# /etc/init.d/networking restart