The best way is to get a good hardware based firewall such as Cisco Guard or Juniper Netscreen 50. What makes you sure that the DDoS attack is targeting your IPs and not your hostname(s). We had seen some DDoS attacks targeting the hostname. In addition, are you sure that your server is under DDoS attack? If your server is under DDoS attack, your server will be down. to detect your public ip address, use
Ip-details.com