I'll try and keep it abstract for you. The concept of DHCP is a protocol which assigns clients addresses to communicate on a network. At the moment, clients in the dorm will (likely) be assigned DHCP addresses from the infrastructure in place which allows devices to connect to the network. DHCP is also built into most consumer grade routers, so that all devices connected to the router are able to interconnect on a LAN.

Once upon a time we had a user plug in his router into our University halls' infrastructure, and the DHCP protocol running on his router was assigning its own addresses to users in the halls faster than University equipment was (DHCP is basically request an address, wait for a response). This resulted in those users being assigned an address from his router, which actually didn't actually provide them with any connectivity at all. This meant a large amount of users within the closest proximity to this router lost connectivity from the actual University network. We had to find the user by using TCPdump to filter for DHCP traffic on an older switch in that block .. it made a good case for the University to begin putting in smarter equipment.

How to prevent this? Don't plug the cable from the ethernet jack into a LAN port on your router unless you have it set to bridge mode, or even simpler, plug into the WAN port instead, creating your own local network.

Hope this helps..