DOS prevention

I have a CentOS web server that has recently been brought to a halt on two
separate occasions.  Checking the access.log, it appears that it was a
Denial of Service (DOS) attack (hundreds of HTTP requests in a very short
time, all from a single IP address).

I want to prevent these types of attacks from bringing the server to its
knees.  We have a hardware firewall (SonicWall) in place, but it isn't
quite new enough to run the firmware that allows rate-limiting.

I have found a number of tutorials that show how to do this type of thing
with IPTABLES.  Is there a better solution?

Supposing I go with IPTABLES, do I need to include rules to allow FTP and
SSH (the only other services on the server)?

Would any of you be willing to assist me with this?

Thanks,
~ j.
[email protected]

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