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.

Alias creation

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

# ifconfig eth0:0  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.

Alias deletion

The alias is removed by shutting the alias down:

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

Alias (re-)configuring

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

Relationship with main device

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