Authentication issues on internal machines if external web server has NTLM authentication

I worked on a case recently  where we had external web server on which we had NTLM authentication and users who were trying to access the website on it were having problems accessing it. I have written blog on our ISA/TMG product team blog here is the link

https://blogs.technet.com/b/isablog/archive/2012/05/25/authentication-failure-while-trying-to-access-a-website-through-tmg-as-forward-proxy.aspx

 

it turned out to be a very interesting issue.