The vary header indicates the request-header fields that the server uses to determine which of multiple cached responses are sent in response to a client request. The default for the OutputCacheSection.OmitVaryStar property is false. By default, ASP.NET sends the vary header in all POST requests, as well as in all GET-request query strings. If the OutputCacheSection.OmitVaryStar is true, ASP.NET omits the vary header when returning the response for cached pages, provided that the GET request to a response is cached with no VaryByCustom property and the POST request to a response is cached with no VaryByParam property and no VaryByCustom property.