In a network that uses Cisco switches, can an unauthorized user connect a laptop to a port and capture usernames and password of employees logging in to their computers? Each port in the wall is connected to a port in the patch panel, and each port in the patch panel is connected to a port on the switch. I understand the above is possible in a hub environment.
There are 2 separate issues here.
The first is nothing to do with the switching infrastructure, it is to do with usernames/passwords being in cleartext or not. This is application specific and so i won't deal with that here.
The second is to do with switches. Unlike hubs switches do not forward unicast frames out of all ports, they only send it to the port with the correct mac-address associated with the unicast packet. Obviously if the packet is a broadcast or the unicast destination is unknown then the switch forwards it out all ports except the one it was received on.
However that doesn't mean that switches are secure with default config. There are many ways to "fool" the switch into doing something it shouldn't. Attached is a link to a good paper on securing campus lan switches -
the specific part you want to look at is "man in the middle attacks" but the whole paper is very useful.