The Vary header indicates the request-header fields that the server uses to determine which of multiple cached responses is sent in response to a client request. The * value specifies that the server selects the response based on parameters not specified in request headers (for example, the network address of the client).

For more information, see RFC 2616: Hypertext Transfer Protocol -- HTTP/1.1, available on the tp://go.microsoft.com/fwlink/?linkid=37125. See section 14, "Header Field Definitions", for complete details.