A NetScaler appliance sometimes sends corrupted forms of valid HTTP headers alongside valid and uncorrupted HTTP headers. The corruption generally appears in the form of swapped bytes in the header name. This is also referred to as "munging."

The appliance can add some extra HTTP headers to HTTP requests during normal operation. These might seem to be corrupted forms of various valid HTTP headers, which are sent alongside the actual valid, uncorrupted HTTP headers.

In this example, an appliance adds the following munged header:
-MIfodified-Since: Wed, 27 Mar 2008 09:14:26 GMT

Alongside the original header, in an HTTP request or response going through the appliance:
If-Modified-Since: Wed, 27 Mar 2008 09:14:26 GMT

HTTP headers are a form of metadata sent with an HTTP message. These headers contain information on how to interpret the message and other useful information about the message. HTTP headers are a part of the Hypertext Transfer Protocol as described in Request for Comments (RFC) 2616.

This behavior is by design.

This style of corruption (swapping bytes) is done for efficiency and for good performance by the appliance when reading HTTP headers, which it might modify during later processing. This is allowed by the HTTP RFC, so that the receiver consider these munged headers as unknown custom headers and ignore them.