Howto block DDOS attacks on Ubuntu

Howto block DDOS attacks on Ubuntu - this ariticle shows the usage of PASD .

What is PSAD ? quoted from its home page:
"psad is a collection of three lightweight system daemons (two main daemons and one helper daemon) that run on Linux machines and analyze iptables log messages to detect port scans and other suspicious traffic. A typical deployment is to run psad on the iptables firewall where it has the fastest access to log data. "

Other tools from the same host:
fwknop - Single Packet Authorization and Port Knocking.

fwsnort - Application Layer IDS/IPS with iptables.

NIDS by Snort

Using Snort: Part 1: Installation and configuration

Using Snort, Part 2: Configuration