1.) Login into the server as the root user
2.) Navigate to /etc/sysconfig/network-scripts directory
3.) Assuming that the network interface name is eth0, cp ifcfg-eth0 as ifcfg-eth0:1
4.) Edit the ifcfg-eth0:1 file and change the DEVICE parameter to DEVICE=eth0:1
5.) Change the other parameters in the NEW file such as IPADDR to the new IP address.
6.) Repeat this process for each additional IP but remember to change the interface name each time e.g. ifcfg-eth0:2
After adding your additional IP’s restart the network service: service network restart