This filter does not do anything with the headers. It looks for a header (X-Forwarded-For by default, but overridable by a ini file). If that header is found, it replaces the contents of the IIS C-IP value with the contents of that header.
It does not add or remove headers so any HTTP header that is passed into it, will be passed on to the web application. There is no rewriting needed as this is just a filter. It just sniffs whats coming in and passes it through to the backend.
So, if a X-Forwarded-For header is passed it to the filter, it will be passed out as well. Are you seeing different behvavior? The source is available for download as well if you want to look for yourself at what the filter does.
-Joe
