sudo apt-get install libapache2-mod-evasive


sudo vi /etc/apache2/mods-available/mod-evasive.conf
add line
<ifmodule mod_evasive20.c>
   DOSHashTableSize 3097
   DOSPageCount  10
   DOSSiteCount  30
   DOSPageInterval 1
   DOSSiteInterval  3
   DOSBlockingPeriod  3600
   DOSLogDir   /var/log/apache2/evasive
</ifmodule>

 sudo a2enmod evasive     
sudo apapache relaod