Fillder for IE 8 resetting automatic configuration script URL

[Ashish Verma]

Hello All,

 

I am bit new for Fiddler tool just started using it sometime back. My project is related to Financial Services so we have to do development inside the VPN. Therefore before starting work first we login into Client VPN and then only anything would be accessible for us. This is web application on which we are working. To run this web application, we need to enable Use Automatic configuration Script URL in IE 8 >> options >> connections >> LAN Setting.  There is valid URL which point .INS file and seems similar to http://qtproxy.xyz.com (its dummy one).

 

Now for capturing the request/response traffic when I open Fiddler it just reset automatic configuration script URL and enable the setting which is just below it "Proxy Server"  and because of this change application stops working.

 

Now If I close the Fiddler and re-specify the URL then application starts working. this is the issue with IE 8 and we are mandate to use this particular browser only.

 

Please help me.

[EricLaw]

Fiddler is a proxy. It works by changing your system's proxy settings to point to itself. By default, it automatically chains to the system's upstream proxy (see Tools > Fiddler Options > Gateway) and forwards requests to the system's proxy, which means your scenario should work just fine.

Now, I think you're saying that you're relying upon an INS file instead of a proper PAC (proxy autoconfiguration) script file. INS is not supported by most of the HTTP stacks on Windows (WinHTTP, System.NET, etc) which means that Fiddler will not chain to the proxy specified inside the INS file and will instead ignore it; you should see a remark about this in the LOG tab when you start Fiddler.

To workaround this, you can manually specify the proxy configuration to which Fiddler should chain using the aforementioned Tools > Fiddler Options > Gateway tab, and you should encourage your IT department to move off of the deprecated INS configuration feature and instead use a PAC file.