IPwatchD is a simple daemon that analyses all incoming ARP packets in order to detect IP conflicts on Linux. It is released under the terms of the GNU General Public License version 2.
IPwatchD can be configured to listen on one or more interfaces (alias interfaces are also supported) in active or passive mode. In active mode it protects your host before IP takeover by answering Gratuitous ARP requests received from conflicting system. In passive mode it just records information about conflict through standard syslog interface.
IPwatchD is available in standard repositories of Debian (details), Ubuntu (details) and Fedora (details). CentOS and Red Hat Enterprise Linux users are encouraged to use EPEL repository.
IPwatchD is also standard part of many enterprise-grade software and hardware products from F5 Networks, Acronis, NETGEAR and others.