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How to prevent DDoS attacks on websites

What is the best way to protect my website from distributed denial-of-service attacks?

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In a distributed denial-of-service (DDoS) attack, the perpetrator uses a large number of systems at many different Internet locations to flood and overwhelm a server with bogus traffic requests. These attacks can be difficult to defend against because of the similarities between attack traffic and legitimate Web requests.

However, there are some actions you can take to protect yourself. Here's some basic advice:

  • Ensure that you have adequate bandwidth on your Internet connection. You'll be able to foil many low-scale DDoS attacks by simply having enough bandwidth (and processing power) to service the requests.
  • Deploy an intrusion prevention system on your network. Some (but definitely not all) DDoS attacks have recognizable signatures that an IPS can detect and use to prevent the requests from reaching the Web server.
  • Use a DDoS prevention appliance, including any of the Cisco Systems Inc. Cisco Guard products, that is specifically designed to identify and thwart distributed denial-of-service attacks.
  • Maintain a backup Internet connection with a separate pool of IP addresses for critical users. While you won't be able to switch all access to your website over to a backup connection (the attacks will switch at the same time!), you can provide critical users with an alternate path to your site if the primary circuit is swamped with bogus requests.

These tips should get you started on the road toward building a hardy Web infrastructure with the highest probability of surviving a DDoS attack. Good luck!

This was first published in April 2009

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