monitor ARP changes in ethernet networks

 The arpalert daemon listens on a network interface (without using
 'promiscuous' mode) and catches all conversations of MAC address to IP
 request.
 It then compares the mac addresses it detected with a pre-configured list of
 authorized MAC addresses. If the MAC is not in list, arpalert launches a
 pre-defined user script with the MAC address and IP address as parameters.
 .
 If you need to use a list of authorized MAC addresses, this package should
 suit your needs, otherwise arpwatch may be also fine.