Hi folks! I've got a bit of a puzzler...
On the 3rd floor of our building, we have three computer labs. Each has it's own switch which connects all of the PC's, printers, etc. Each of those three switches then has a CAT6 cable which connects them back to a backbone switch in our main server room on the 1st floor. That switch is then connected to our router/firewall, a SonicWALL TZ-210.
There is one switch/room on that floor which is essentially killing the whole network if it is connected. If I pull power to that switch, everything in the other two labs functions fine. If I connect it, then computers will successfully find the DHCP server and get an IP address, but that's it. They won't be able to log in via Active Directory, they won't be able to ping the router, they will only very intermittently be able to ping each other. Disconnect the room in question and instantly everything else works again.
Clearly, either the switch is malfunctioning/misconfigured or there is a device connected in that room that is doing something it shouldn't. I'm trying to narrow it down, though, by determining what exactly could cause these symptoms.