Is there a way to rebuild the tcp/ip stack in a MAC if this is the only solution available?

MAC is the address of your ethernet device.

Mac OS is the operating system. :P

And yes, simply go into system preferences and toss the preference file.

I think its here -> HD>Library>Preferences>System Configuration>preferences.plist

Although I doubt that's your problem, I think the Cisco client is the issue. Don't know if it will work, but best bet is to reinstall the client.

Hey I'm an F'n Jerk!