The machine that I am using to run some penetration tests on a network has two networking interfaces, one of them is onboard but I am unable to remove it so I added another interface in one of the expansion slots and everything started working fine. But when it came to using ettercap to run some man in the middle tests, nothing worked. This test wasn't successful since ettercap seems to only work with the default networking interface for man in the middle attacks and I am not using the default (the on board NIC) interface because the one I added is much quicker. This penetration test is useless without a successful man in the middle attack and since ettercap only does successful man in the middle attacks with the default interface it looks like it won't get done.

I really appreciate all of the help