A SYN flood is an attack is a basic DOS attack. Basically, it uses one of the foundation steps in an internet or intranet connection to a server, where a computer sends a syn, or synchronize, request to the server, and exploits it. The way the connection works is that the client sends a syn request to the server, the server responds with the command syn-ack and then the client finishes the connection to the server by sending an ack command back to the server.
One of the best tools used to plan and use this attack would be hping. Hping is like the ping command in command prompt but you get a few more options. It comes with BackTrack by default and is easy to download and install to any linux distro. To do so, copy and paste the following into your terminal:
aptitude install hping2
note: the installation above may require root/sudo privileges to execute.
To attack a website type in the following into your terminal:
hping -i u1 -S -p 80 ip-address
The default is port 80, or the HTTP port, but you can choose any port that you would like.
For more information on the mechanics of a SYN flood attack, goto:
http://en.wikipedia.org/wiki/Syn_flood
or check out this site to learn on how to defend or get around defenses for a SYN flood attack:
http://www.usenix.org/events/sec01/invi ... oliver.pdf