In some cases, it might not be that easy to detect an attack. For instance, in a HTTP DDoS attack, a web server might be attacked with legitimate traffic; therefore they are regular HTTP requests. This is where we can use HTTP DoS protection. HTTP DoS protection allow NetScaler to respond with a JavaScript challenge to all incoming HTTP requests. Since a HTTP DDoS attack is typically done using a cluster of many nodes running a scripted attack, these nodes do not support any form of JavaScript request; therefore, when they cannot respond to the JavaScript challenge, NetScaler closes the connection. Regular users surfing with a regular browser support JavaScript and are therefore granted access. This happens in the background and the user never sees that it happens. Enabling HTTP DoS puts a lot of strain on NetScaler, especially if there is a lot of traffic and the client detect rate is at 100 percent.
In order to enable HTTP DoS, go into Security | Protection Features...