Frequently I see customers trying to verify if their Kerberos settings (http://bit.ly/QOEvLF) are truly working or not. In the past we’ve used tools such as NetMon, Kerbtray, Klist, and others to verify this however, recently I found a very simple way to test if Kerberos auth is working or not using Fiddler – a very common utility that many admins already have loaded on their client machines. Here are the steps:
If you were expecting to see YII and see TlR instead, please take a look at my other blog posting (http://bit.ly/QOEvLF) covering the setup and configuration of SPN’s and Active Directory properties to allow for proper Kerberos authentication. Also, once Kerberos is functioning I recommend taking advantage of IIS’s AuthPersistNonNTLM setting to reduce the number of 401 challenges – this is also covered in the Kerberos blog posting under section 3.1.
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You can also look under inspectors again and then select 'Auth' and this will show you either Kerberos or NTLM authentication very clearly.
Great tip @Gavin - thanks!
I have had various occasions when having Fiddler on changes the way Kerberos is functioning ...
For instance, with Fiddler open it looks like Internet Explorer is sending a Kerberos ticket with every request, even after AuthPersistNonNTLM is set ... in fact with Fiddler open it does do that. But with Fiddler closed, it does not.
I was able to verify this with a "netsh trace" both with Fiddler open and again with it closed.
Also in some scenarios Kerberos outright fails when Fiddler is running, but works otherwise. Again verified with a "netsh trace"
All of these problems were with IE... chrome didn't seem to care if Fiddler was running or not.
I guess it has something to do with how Fiddler inserts itself as a proxy. Not sure why IE is the only one that cares. Anyway your users might want to double check "kerberos failures" using a less intrusive system. Just thought I'd mention it ...