Avoiding 401 response for each request using NTLM

Question

We have here an asp.net 3.5 application using NTLM based windows authentication. The system runs on a private network that actually distributed over different geographic pla

Answer 1

NTLM/Negotiate, unlike all other HTTP authentication schemes, are connection-oriented protocols.

In IIS, there are various settings which control whether authentication will be demanded for all requests on a previously authenticated connection (e.g. AuthPersistSingleRequest). Independent of that setting, I believe IIS will automatically demand re-authentication when making a POST request.

If your server is impairing connection reuse (e.g. by sending a Connection: close header in responses) you must fix that because otherwise the reauthentication will occur. You can easily check for such authentication-reuse foiling headers using Fiddler.