mod_evastive

cd /usr/local/src

Download the module
wget http://www.zdziarski.com/blog/wp-content/uploads/2010/02/mod_evasive_1.10.1.tar.gz

Untar
tar zxvf mod_evasive_1.10.1.tar.gz

Go to the folder
cd mod_evasive

Compile it
/usr/sbin/apxs -cia mod_evasive20.c

Add to apache config file
/etc/httpd/conf/httpd.conf

<IfModule mod_evasive20.c>
DOSHashTableSize 3097
DOSPageCount 6
DOSSiteCount 100
DOSPageInterval 2
DOSSiteInterval 2
DOSBlockingPeriod 600
DOSEmailNotify root@domain
</IfModule>

Restart apache
/etc/init.d/httpd restart

You can test the modules with
perl test.pl