Maybe you have heard of Slowloris?
Slowloris is a type of denial of service attack invented by Robert “RSnake” Hansen which allows a single machine to take down another machine’s web server with minimal bandwidth and side effects on unrelated services and ports.
If you want to protect from it you can install mod_antiloris
1) Download the installer from sourceforge and install
tar -xvjf mod_antiloris-0.4.tar.bz2
apxs -a -i -c mod_antiloris.c (if this command do not work use apxs2 instead)
2) Now restart Apache
service httpd restart
3) check whether mod_antiloris loaded or not
httpd -M | grep antiloris
Note if you are using cpanel server then you have to run the below command to make sure new modification are updated into configuration system file