A virtual IP is an ip that bind to a physical ethernet card that already has a physical ip address.
1. Add virtual ip to eth0.
Here is the original configuration of /etc/sysconfig/network-scripts/ifcfg-eth0. ifcfg-eth0 is the original configuration file for eth0.
vi /etc/sysconfig/network-scripts/ifcfg-eth0
BOOTPROTO=static BROADCAST=192.168.0.255 HWADDR=00:0C:29:C8:AA:7C IPADDR=192.168.0.10 NETMASK=255.255.255.0 NETWORK=192.168.0.0 ONBOOT=yes TYPE=Ethernet
2. Create a new virtual configuration file by copying and editing the ifcfg-eth0 configuration file.
Change the IPADDR and remove HWADDR.
cd /etc/sysconfig/network-scripts cp ifcfg-eth0 ifcfg-eth0:0 vi ifcfg-eth0:0
BOOTPROTO=static BROADCAST=192.168.0.255 IPADDR=192.168.0.11 NETMASK=255.255.255.0 NETWORK=192.168.0.0 ONBOOT=yes TYPE=Ethernet
3. Restart network
/etc/init.d/network restart
4. Check your new virtual ip using ifconfig
ifconfig