Hi,
The easy way to do this is to create a virtual interface/reference and assign the additional ips to them.
For CLI I use the method of copying the ifcfg-eth0 file in /etc/sysconfig/network-scripts/ the ifcfg-eth0 file should appear similar to the below copy (I have edited all networking information to private/reserved lan IPs).
Code:
DEVICE=eth0
BOOTPROTO=static
BROADCAST=192.168.1.255
HWADDR=xx:xx:xx:xx:xx:xx
IPADDR=192.168.1.3
GATEWAY=192.168.1.1
NETMASK=255.255.255.0
NETWORK=255.255.1.0
ONBOOT=yes
I will call the copy something like ifcfg-eth0:1 and then opening the file you change the device to eth0:1, change the IP information as required and remove the HWADDR field as this should not be required and depending on the networking configuration other details may also not be required (I.E. Gateway). I have given a simple configuration below of the ifcfg-eth0:1 configuration, you will note the only change is the IP what has gone from a .3 to a .12.
Code:
DEVICE=eth0:1
BOOTPROTO=static
BROADCAST=192.168.1.255
IPADDR=192.168.1.12
GATEWAY=192.168.1.1
NETMASK=255.255.255.0
NETWORK=255.255.1.0
ONBOOT=yes