You could add your additional ips to your existing NIC on your CentOs server in following steps ;
Please create a /etc/sysconfig/network-scripts/ifcfg-eth0:1 and copy the existing main ip's settings to this file ;
cp /etc/sysconfig/network-scripts/ifcfg-eth0 /etc/sysconfig/network-scripts/ifcfg-eth0:1 ( if you have several additional ips to add you need to repeat this and another steps as well as eth0:2 ,eth03...etc)
configured and matched to additional ip's settings;
nano /etc/sysconfig/network-scripts/ifcfg-eth0:1
up it ;
# ifup eth0:1
restart network services ;
service network restart
