Copy an existing configuration file

Head into the directory housing the config scripts:
cd /etc/sysconfig/network-scripts
And create a duplicate from an already working entry:
cp ifcfg-eth0 ifcfg-eth0:1

Amend the new file

Open the file for editing:
nano ifcfg-eth0:1
Alter the IP address, subnet mask etc as required, it’ll look a little like this:

DEVICE=eth0
BOOTPROTO=static
HWADDR=00:25:64:3B:3F:DF
IPADDR=212.84.187.130
NETMASK=255.255.255.248
ONBOOT=yes

Bring the new interface up

Simply run:
ifup eth0:1