I am in charge of a local network in a dormitory, we have two 50-way switches and using them to connect to some remote router which is not administered by me (it is not in my building). Note: this is a legacy setup, I had no decision on how it is put together. So, normally someone connects his comp and gets an IP address from that router using DHCP.
However recently people connecting their computer are not able to connect to the net and get their IP from a different router. How is this possible? Someone just connected his own router to the network and steals DHCP requests? If so, how can I find the culprit?