Dedicated server DDoS protection

Hello, I am searching for a specialist in linux configuration regarding DDoS protection (SYN/UDP flood, etc.), networking (IP table configuration, etc.) My company website which is hosted on a dedicated server is currently suffering from a DDoS attack. I need a specialist to diagnose the problem, stop the attack and finally configure IP tables and secure my server as much as possible from most types of DDoS attacks. It should be noted that the website is used by users from all over the world, so the remedy needs to some how filter the good international traffic from the bad one. Additional information: Operating System: CentOS 64bit w/ PLESK When I type #netstat -tn 2>/dev/null | grep :80 | awk '{print $5}' in the ssh console a list of about 120 connections/ips appear and they rotate with some frequency. So the attach is dynamic. The server is stable when a under maintenance page is used, but as soon as the [login to view URL] is placed the server crashes. Priority will be given to the freelancer with experience and availability.