Arpwatch

Arpwatch is a tool that monitors ethernet activity and keeps a database of ethernet/ip address pairings. It also reports certain changes via email. Arpwatch uses libpcap, a system-independent interface for user-level packet capture. Before building tcpdump, you must first retrieve and build libpcap, also from LBL, in: ftp://ftp.ee.lbl.gov/libpcap-*.tar.Z.