Denial of Service (DoS)

Denial of service attacks are most common to take website and servers down. It is easy to attack and hard to protect. The way to prevent of an attack is to block the response to the attackers. Catch the attacker as early as possible after the request has been received by the web server.

There are two challenges to blocking the attacks

• Identify the attackers

• Block the response only to the attackers

First to catch the request as early as possible, an HttpModule is the right place. It is executed before any page or any other handler so the impact on the server can be minimized. This HttpModule monitors all requests and block requests coming from IP addresses that make many requests in a short period of time. After a while the attacking IP address gets released from blocking.

Implementation

Download the DosAttackModule.cs file below and put it into the App_Code folder of your website. Then add the following lines to the web.config’s <system.web> section:

< httpModules >

< add type = " DosAttackModule " name = " DosAttackModule " />

</ httpModules >