I was trying to track down why my site was so painfully slow in IE9 when I pulled out Fiddler and realised that every request is being sent 3 times (twice I get 401.2 and then a success). I verified this happens on all browsers, its just that Chrome's speed was masking this (or it could be that this has nothing to do with my sites performance issues in IE).
I've set up break points in my begin/end request handlers and the request comes in for say a css file. It is not authenticated and the response goes out with a 401.2, I doubled checked that I'm not setting the response status anywhere myself, so somewhere between begin_request and end_request the status is changing to 401.2
Note: I have the runAllManagedModulesForAllRequests=true so I can configure compression, however this setting does not affect this (from what I can see from Fiddler).
I am very ignorant on kerberos/active directory in general but I just cannot fathom that this is a normal handshaking protocol for every single request (perhaps for the first? but not all).
I have scoured the googles and nothing seems to help (adding/removing modules/authentication providers, etc). I mean my site works just fine, its only once you look under the hood that I see the treplicated requests. Note: This also happens when I deploy to production so its not a server specific issue.
Has anyone ever seen this? thanks in advance.
I think this is how NTLM authentication works. The process is discussed here. Note that you will want to set AuthPersistSingleRequest to false to cut down on the number of 401s
来源：https://stackoverflow.com/questions/16973841/3-requests-for-every-resource-2-x-401-2-and-1-x-200-in-a-windows-authenticated