Anti DDOS Script Configuration and Sever Firewall Config

We are currently experiencing a wide array of problems relating to DDOS attacks on our website. We need someone who has extensive experience in mitigating these attacks to help us out with the following. 1. Write a script that can reduce the frequency of the attacks. 2. Configure a solid firewall solution on our server to filter malicious IP's. 3. Optimize our server so that we can get good production grade speeds once again. The candidate must have extensive experience in systems administration, and mitigating DDOS attacks.