An easy way to have 2 IP addresses is to have your router assign a DHCP adress as usual (wlan0 or eth0) and then set an IP address (with ifconfig) for wlan0:1 or eth0:1. If you do it that way, make sure you stay away from the pool of DHCP addresses that can be assigned, otherwise you may end up with a network nightmare...

You are in a maze of twisty little passages, all alike.
When General Failure and Major Disaster get together, Private Parts usually suffers.