C# – Can’t Get Fiddler to Capture local traffic to IIS

asp.netcfiddleriis

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:
  • 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

Best Answer

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?

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