If you are being attacked or abused by a particular host, just enter the following command to deny all access to the host:
/sbin/route add -host <ip address> reject
Replace with the IP address of the host you want to block. The address will stay blocked until you bounce the interface. Alternatively, you could allow access by:
/sbin/route del -host <ip address> reject
For a more permanent rejection, of course, use your firewall. If you really want this to persist, add the command to rc.local or whatever your favorite is.
Do note that these options don’t work with the XP/Windows 2000 route command. These options do work with Linux, and may work with other *nix systems. We have only tested with Linux.