How to limit request rate per IP to a php web site ?

You can try using ModSecurity. I found this article that might be helpful, I recommend checking it out. https://secure.jwall.org/blog/2009/07/19/1248004300834.html

Take a look here: http://www.tek-tips.com/viewthread.cfm?qid=1496716 http://stackoverflow.com/questions/5761851/limit-page-request-with-php

See that link : http://www.tek-tips.com/viewthread.cfm?qid=1496716