Can't Get Fiddler to Capture local traffic to IIS

Question

I have recently installed the latest Fiddler (Fiddler4) and absolutely nothing that I try is working to get it to capture local traffic. I have an MVC application that is connecting to an MVC WebApi app both running on IIS, here's what I've tried:

• Fiddler Options > Connections > Monitor All Connections & Use PAC Script
• Changed the WebClient C# call to use the following URLs with no success:
  • http://machinename/app-name
  • http://localhostproxy.com/app-name
  • all of the ipv4 / ipv6 etc urls on this page http://fiddler2.com/documentation/Configure-Fiddler/Tasks/MonitorLocalTraffic
  • also tried using the . fix - http://localhost.
• Changed my "Default Website" in IIS to run under a new AppPool that uses my local account, and ran Fiddler as administrator
• added <system.net> <defaultProxy> <proxy bypassonlocal="False" usesystemdefault="True" /> </defaultProxy> </system.net> to my web.config of the MVC app.

Nothing has worked, I have no idea what to try. Any advice is greatly appreciated. Thanks, Shawn

Answer 1

It turned out that I needed to set up Fiddler as a reverse proxy (http://fiddler2.com/documentation/Configure-Fiddler/Tasks/UseFiddlerAsReverseProxy). I don't really understand why before I upgraded from Fiddler2 to Fiddler4 I didn't have to do this. I used to be able to just use http://ipv4.localhost/app-name and all worked fine. In order to get it working with Fiddler4, though, I set-up the reverse proxy, and then changed all my requests from http://ipv4.localhost/app-name to http://machinename:8888/app-name. I can now listen in to inter-app communications. Any idea why I didn't have to do this with Fiddler2, but I now do after upgrading to Fiddler4?