We are installing mod_dosevasive apache module on all servers in order to be able to better fait against DDOS attacks targeted to webserver.
It is hard to close them with normal firewall especially when they are targeted on just a certain user. Also this module should decrease a number of atacks targeted on exploiting user forums, formmail scripts etc.

So far it sounds good but also this mofule potentially can create problem with search engines or chats. Please, let our support know if you have any problems with it and we'll tweak module settings to solve it.


Below you'll find a description of the mod_dosevasive.
QUOTE
What is mod_dosevasive?

mod_dosevasive is an evasive maneuvers module for Apache to provide evasive action in the event of an HTTP DoS or DDoS attack or brute force attack. It is also designed to be a detection and network management tool, and can be easily configured to talk to ipchains, firewalls, routers, and etcetera. mod_dosevasive presently reports abuses via email and syslog facilities.

Detection is performed by creating an internal dynamic hash table of IP Addresses and URIs, and denying any single IP address from any of the following:
Requesting the same page more than a few times per second
Making more than 50 concurrent requests on the same child per second
Making any requests while temporarily blacklisted (on a blocking list)

This method has worked well in both single-server script attacks as well as distributed attacks, but just like other evasive tools, is only as useful to the point of bandwidth and processor consumption (e.g. the amount of bandwidth and processor required to receive/process/respond to invalid requests), which is why it's a good idea to integrate this with your firewalls and routers for maximum protection.

This module instantiates for each listener individually, and therefore has a built-in cleanup mechanism and scaling capabilities. Because of this per-child design, legitimate requests are never compromised (even from proxies and NAT addresses) but only scripted attacks. Even a user repeatedly clicking on 'reload' should not be affected unless they do it maliciously. mod_dosevasive is fully tweakable through the Apache configuration file, easy to incorporate into your web server, and easy to use.