From : http://www.ddosdefense.net/
(1st Google result for ‘ddos defense’)
If a mitigation service is too expensive, there are things IT can do to lower the exposure and limit the damage from DDoS attacks (discussed more in depth in our full report):
1. Fortify your edge network: Ensure that firewall and IDS systems have DoS features turned on, including things like dropping spoofed or malformed packets, setting SYN, ICMP, and UDP flood drop thresholds, limiting connections per server and client, and dynamically filtering and automatically blocking (at least for a short time) clients sending bad packets.
2. Develop a whitelist of known good external systems: These include business partner gateways, ISP links and cloud providers. This ensures that stringent edge filtering, whether done on your firewall or by a DDoS service, lets good traffic through.
3. Perform regular audits and reviews of your edge devices: Look for anomalies like bandwidth spikes. This works best if the data is centrally collected and analyzed across every device in your network.
4. Understand how to identify DDoS traffic: Research attack signatures and have someone on your network team who knows how to use a packet sniffer to discriminate between legitimate and DDoS traffic.
5. Prepare DNS: Lower the DNS TTL for public-facing Web servers, since these are most likely to be attacked. If you need to protect an entire server subnet, have a plan to readvertise BGP routes to a mitigation service.
6. Keep public Web servers off your enterprise ISP link: With Web servers being the most common DDoS target, Michael Davis, CEO of Savid Technologies and a regular InformationWeek contributor, recommends Web hosting with a vendor that doesn’t share your pipes. “Your website may be down, but at least the rest of your business is up,” says Davis.
7. Practice good server and application security hygiene: Layer 7 attacks exploit operating system and application security flaws, often using buffer overflows to inject attack code into SQL databases or Web servers, so keep systems patched.
There’s lots of additional information as well.