Usually there is some pattern to the traffic that can be identified and filtered out. There are manual ways to do this (iptables, basic firewalls) or more sophi

Usually there is some pattern to the traffic that can be identified and filtered out. There are manual ways to do this (iptables, basic firewalls) or more sophisticated "anti-DDOS" boxes you can buy to automate or simplify the process (e.g. Cisco Anomaly Guard or Juniper Junos DDoS Secure).