Filter features using classic policies are deprecated and as an alternative Citrix recommends you to use the rewrite and responder features with advanced policy infrastructure.

Today’s complex Web configurations often require different responses to HTTP requests that appear, on the surface, to be similar. When users request a webpage, you may want to provide a different page depending on the user geographical location, browser specification, or languages the browser accepts and the order of preference. You might want to drop the connection if the request is coming from an IP range that has been generating DDoS attacks or initiating hacking attempts.

Responder supports protocols such as TCP, DNS (UDP), and HTTP. With responder enabled on your appliance, server responses can be based on who sends the request, where it is sent from, and other criteria with security and system management implications. The feature is simple and quick to use. By avoiding the invocation of more complex features, it reduces CPU cycles and time spent in handling requests that do not require complex processing.

For handling sensitive data such as financial information, if you want to ensure that the client uses a secure connection to browse a site, you can redirect the request to a secure connection by using https:// instead of http://.

To use a responder, do the following:

  • Enable a responder feature on the appliance.
  • Configure a responder action. The action can be to generate a custom response, redirect a request to a different webpage, or reset a connection.
  • Configure a responder policy. The policy determines the requests (traffic) on which an action has to be taken.
  • Bind each policy to a bind point put it into effect. A bind point refers to an entity at which the NetScaler appliance examines the traffic to see if it matches a policy. For example, a bind point can be a load balancing virtual server.

You can specify a default action for requests that do not match any policy, and you can bypass the safety check for actions that would otherwise generate error messages.

The Rewrite feature of NetScaler helps in rewriting some information in the requests or responses handled by NetScaler. The following section shows some differences between the two features.

Comparison between Rewrite and Responder options

The main difference between the rewrite feature and the responder feature is as follows:

Responder cannot be used for response or server-based expressions. Responder can be used only for the following scenarios depending on client parameters:

  • Redirecting an HTTP request to new websites or webpages
  • Responding with some custom response
  • Dropping or resetting a connection at request level

If there is a responder policy, the NetScaler examines the request from the client, takes action according to the applicable policies, sends the response to the client, and closes the connection with the client.

If there is a rewrite policy, the NetScaler examines the request from the client or response from the server, takes action according to the applicable policies, and forwards the traffic to the client or the server.

In general, it is recommended to use a responder if you want the appliance to reset or drop a connection based on a request-based parameter. Use a responder to redirect traffic, or respond with custom messages. Use rewrite for manipulating data on HTTP requests and responses.