nano /etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE=eth0
TYPE=Ethernet
ONBOOT=yes
BOOTPROTO=dhcp
IPV4_FAILURE_FATAL=yes
NAME="System eth0"
service network restart

Useful Link:

https://www.serverlab.ca/tutorials/linux/administration-linux/configure-centos-6-network-settings/