I have website abc.com and abc.co.in.I have two webservers also. The following issue happens only in abc.co.in with same application deployed on same. We have written a custom IHttpModule and do a rewrite to abc.co.in?some=data. Expected behavior: When user enters some.abc.co.in the expected behavior is browser still display some.abc.co.in but internally call abc.co.in?some=data Actual behavior: The page is rendered properly but in browser the URL changes to some.abc.co.in?some=data I checked what is happening 1.First the server receives the request and does a 301 redirect. 2.The redirect location is some.abc.co.in?some=data I am stuck in this for a day and critical to fix to make our site up and running. How to debug this issue further ?.Any one can think of possible cause? ETW Trace shows <ApplicationData> <TraceData> <DataItem> <OldUrl>/</OldUrl> <NewUrl>/fp?&id=hazzel&params=</NewUrl> </DataItem> </TraceData> </ApplicationData> <ApplicationData> <TraceData> <DataItem> <ModuleName>DefaultDocumentModule</ModuleName> <Notification>128</Notification> <HttpStatus>301</HttpStatus> <HttpReason>Moved Permanently</HttpReason> </DataItem> </TraceData> </ApplicationData> <ApplicationData> <TraceData> <DataItem> <Headers>Content-Type: text/html; charset=UTF-8 Location: http://some.abc.co.in/fp/?id=data Server: Microsoft-IIS/7.5 X-Powered-By: ASP.NET </Headers> </DataItem> </TraceData> </ApplicationData>