With Snort2Pf, you can turn your local Snort
installation easily into an "intrusion detection
and prevention system", rather than simply using
it for post-mortem analysis. Such a system also
blocks the recognized violations.
arpalert uses ARP address monitoring to help
prevent unauthorized connections on the local
network. If an illegal connection is detected, a
program or script is launched, which could be used
to send an alert message, for example.