How can I add external Interface to my OS X with a valid IP? I connect my Macbook pro to internet through Lan and if I type ifconfig in terminal my en0 interface get valid IP now I want add en1, en2 and en3 to my configuration and they all be able to get valid IPs, I don't want to add additional network card I just want to use my internal network card. I don't know if I must use bridging or nating or ... . please help find my solution.
In System Preferences -> Network click on the + to add a new interface, in the popup choose Ethernet.
This will not create an additional en1 or en2 interface, but add an additional address to your en0 interface.