Adds a TARPIT target to iptables, which captures and holds incoming TCP
connections using no local per-connection resources.  Connections are
accepted, but immediately switched to the persist state (0 byte window), in
which the remote side stops sending data and asks to continue every 60-240
seconds.  Attempts to close the connection are ignored, forcing the remote
side to time out the connection in 12-24 minutes.

This offers similar functionality to LaBrea
<http://www.hackbusters.net/LaBrea/> but doesn't require dedicated hardware
or IPs.  Any TCP port that you would normally DROP or REJECT can instead
become a tarpit.

To tarpit connections to TCP port 80 destined for the current machine:

  iptables -A INPUT -p tcp -m tcp --dport 80 -j TARPIT

To significantly slow down Code Red/Nimda-style scans of unused address
space, forward unused ip addresses to a Linux box not acting as a router
(e.g. "ip route 10.0.0.0 255.0.0.0 ip.of.linux.box" on a Cisco), enable IP
forwarding on the Linux box, and add:

  iptables -A FORWARD -p tcp -j TARPIT
  iptables -A FORWARD -j DROP

You probably don't want the conntrack module loaded while you are using
TARPIT, or you will be using resources per connection.