Cannot design a secure net that allows guests?
Of course I can design a secure network that allows guests. I do it at hotels.
However, a "guest" would indicate that they have *permission* to be on the Network, as well as being set up with any credentials they need.
A "guest" would never have any reason to run a packet sniffer on my network. A *consultant* that I bring in might, under my supervision, if I were having unsolvable network problems or traffic issues.
The reality of it is, however, that a "guest" would never need to be sniffing about on my network. It *IS* part of our secure network to make sure that things like that don't happen, because it compromises everyone ELSE'S security.
Now, considering the original post....
A vendor or customer come in the premise, boot up their notebook, obtain ip thru dhcp, and connect to the internet. While online, they run their network sniffer to sniff internal traffic or scanner to see what's on your domain network.
.... that is not a guest. That is a hacker. They are being nosey, or subversive, or even (at worst) in the middle of corporate espionage.
How would you feel if this happened at your home, while you were doing your online banking, or sending an IM to a "special friend"? Not that I'm hiding anything at work, mind you, but by the same token, since we are health care/corrections, there is very sensitive data on our network.
For that matter, we don't even allow a vendor in the building without signing a HIPAA compliance form, and that includes the guy that fills the candy machine in the basement!
Just my 2¢
"In order to start solving a problem, one must first identify its owner." --Me
--Greg