I never notice that IIS Express doesn’t listen to web requests other than localhost. So, to my surprise, when I try http://127.0.0.1, I got HTTP 400, Bad Request instead.
Change 127.0.0.1 to localhost and everything is fine.
Anyway, you can set your IIS Express to let it listen to a request for 127.0.0.1 easily.
1. Look for a file applicationhost.config. It’d be under /documents/IISExpress/config.
2. Go to <sites> section and look for your site. In this example, I have my web project named MyWeb.
3. Change localhost to 127.0.0.1
4. Stop IIS Express and run your web site again.
Now you should be able to access your web site thru 127.0.0.1 address now!
Hope this helps! 🙂
Cyan By Fuchsia 
OMG this has been driving me INSANE. I just upgraded from Visual Studio 2013 to 2015 and my web app suddenly started giving 400 errors when trying to use 127.0.0.1
Out of curiosity, do you have any idea why running under VS2015 would give a 400 error when VS2013 used to accept 127.0.0.1?
Thankyou so much!
Sure it helps! More than one hour trying to solve the problem, thank you!
Still same error
I was missing the last step “4. Stop IIS Express and run your web site again.”
Thanks for the article!