Fail2Ban is a small service to block unwanted traffic to you server. I use it to block ssh,and postfix loggins in to my virtual hosts.
Fail2Ban scans the service loggfiles and if it find any strange traffik like ssh bruteforce. That ip will be blocket for some time.
All settings are done in /etc/fail2ban/ folder.
Have epel repo aktivated on server tha run
yum install fail2ban
Then do your local config in
Activate and restart fail2ban
chkonfig fail2ban on /etc/init.d/fail2ban restart
If you looking for more advanced host based monitoring OSSEC (http://www.ossec.net/ )is i realy nice tool
And it handels many agente to one server.