Kernel-3.10.0-957.el7_alias

IP-Aliasing:

IP-aliases are an obsolete way to manage multiple IP-addresses/masks
per interface. Newer tools such as iproute2 support multiple
address/prefixes per interface, but aliases are still supported
for backwards compatibility.

An alias is formed by adding a colon and a string when running ifconfig.
This string is usually numeric, but this is not a must.

o Alias creation.
Alias creation is done by ‘magic’ interface naming: eg. to create a
200.1.1.1 alias for eth0 …

# ifconfig eth0:0 200.1.1.1  etc,etc....
               ~~ -> request alias #0 creation (if not yet exists) for eth0

The corresponding route is also set up by this command. 
Please note: The route always points to the base interface.

o Alias deletion.
The alias is removed by shutting the alias down:

# ifconfig eth0:0 down
             ~~~~~~~~~~ -> will delete alias

                    

o Alias (re-)configuring

Aliases are not real devices, but programs should be able to configure and
refer to them as usual (ifconfig, route, etc).

o Relationship with main device

If the base device is shut down the added aliases will be deleted
too.