We have a medium sized network and from time to time something bad happens. Once it was a router configured to assign IPs via DHCP that did not match our network mask, thus making all clients unable to access the internet through our router, and another time it was some network attached device that occupied the IP of our router (somebody had set a fix IP address to it, creating a collision).
In both cases I could see which MAC address was causing the problem, but then I had the problem of trying to track the device down by going to each switch and unplugging one line after the other to find out if the problem persists.
Is there a simple way to avoid these problems, by overriding the DHCP assignment or isolating the rogue device?