PHREL is a Per Host RatE Limiter.

It will track the rate of incoming traffic to a server and insert
insert a chain into iptables when a configured threshold is crossed.
The inserted chain may either rate limit or block the offending host
for a period of time.

It is particularly well suited to protecting nameservers (DNS) from 
random flood requests.

Please see: phreld(1) and phreld.conf(5) for post-install configuration,
and /etc/rc.d/rc.local for daemon auto-start.