Arpwatch

Arpwatch is an Open source Software that monitors a computer network for Address Resolution Protocol-activity. The first and foremost reason to monitor ARP activity is to detect ARP spoofing. It is developed by Lawrence Berkeley National Laboratory, Network Research Group, and released under the BSD license. The source is available [http://www-nrg.ee.lbl.gov/ http://www-nrg.ee.lbl.gov/].