From
http://www.siliconvalleyccie.com/lin...ork-linux.htm:
Multiple IP Addresses on a Single NIC
In the previous section "Determining Your IP Address" you may have noticed that there were two wireless interfaces: wlan0 and wlan0:0. Interface wlan0:0 is actually a child interface wlan0, a virtual subinterface also known as an IP alias. IP aliasing is one of the most common ways of creating multiple IP addresses associated with a single NIC. Aliases have the name format parent-interface-name:X, where X is the sub-interface number of your choice.
The process for creating an IP alias is very similar to the steps outlined for the real interface in the previous section, "Changing Your IP Address":
1. First ensure the parent real interface exists
2. Verify that no other IP aliases with the same name exists with the name you plan to use. In this we want to create interface wlan0:0.
3. Create the virtual interface with the ifconfig command
[root@bigboy tmp]# ifconfig wlan0:0 192.168.1.99 \
netmask 255.255.255.0 up
4. You should also create a /etc/sysconfig/network-scripts/ifcfg-wlan0:0 file so that the aliases will all be managed automatically with the ifup and ifdown commands. Here is a sample configuration:
DEVICE=wlan0:0
ONBOOT=yes
BOOTPROTO=static
IPADDR=192.168.1.99
NETMASK=255.255.255.0
The commands to activate and deactivate the alias interface would therefore be:
[root@bigboy tmp]# ifup wlan0:0
[root@bigboy tmp]# ifdown wlan0:0
Note: Shutting down the main interface also shuts down all its aliases too. Aliases can be shutdown independently of other interfaces.
