ubuntu 12.04 lts server eth0 and eth1 are missing

1)
Goto following file and add eth0 and eth1
sudo vim /etc/network/interfaces

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet dhcp

auto eth1
iface eth1 inet dhcp

2)
Remove following line
sudo rm /etc/udev/rules.d/70-persistent-net.rules

3)
Restart networking
#sudo reboot
sudo /etc/init.d/networking restart