Hope you can make use of the firewalls than this iptables. Better to make use of csf fire wall.
Here are the things to install a csf firewall and to block a particular IP
1) Log into your server and switch to the root user
2) Switch directories to your download directory
3) Download the latest version of the software: # wget
http://www.configserver.com/free/csf.tgz
4) Untar the package: # tar -xzf csf.tgz
5) Switch into the new extracted folder: # cd csf
6) Run the installer: # sh install.sh
7) If you are still running APF and BFD on your server it is necessary to disable those applications: # sh disable_apf_bfd.sh
after this just use the command csf -d <ip that you want to block>
eg: csf -d 127.0.0.0
If you are running WHM you can now configure CSF and LFD from WHM. CSF/LFD comes pre-configured for a cpanel/WHM server and so there is not that much to do after the installation. Log into WHM and inspect the new configuration utility. As an example you can uninstall APF and BFD from here with the click of the button. If you want to manually edit the CSF/LFD configuration you can do so at / etc/csf/*. Make sure to make backups before you make changes as well as using the debug mode to avoid being locked out.
If for whatever reason you need to uninstall CSF and LFD you can do this easily yourself as well. Login to your server via SSH and switch to the root user.
1) Switch to the folder holding the uninstaller: # cd /etc/csf
2) Run the uninstaller: # sh uninstall.sh