Fiddler doesn't show traffic between .NET Core 6 app and Firefox

[NIKOLAY]

Hi,

 

I set Fiddler as a proxy per this official link , but when I ran my NET Core app in Visual Studio and Firefox I noticed that no requests between FF and my app were displayed in Fiddler. At the same time, all requests from Firefox to the Internet were shown excellently. All applications (Visual Studio, Fiddler and Firefox) were run under administrative account on my machine. What should I do to have requests from FF to  my NET Core app shown in Fiddler?

OS: Win 10 x64 Pro 21H2 (19044.1526)

Firefox: 103.0.2 (64-bit)

Fiddler: v5.0.20211.51073 for .NET 4.6.1 Built: Wednesday, December 15, 2021 64-bit AMD64, VM: 75.0mb, WS: 125.0mb .NET 4.8 WinNT 10.0.19044.0

Visual Studio: Microsoft Visual Studio Community 2022 (64-bit) - Version 17.3.0

[Nick Iliev]

Hi Nikolay,

Refer to this documentation article for details on how to configure your NET Core application to respect the Fiddler proxy.

 

Regards,
Nick Iliev
Progress Telerik

[NIKOLAY]

Hi Nick,

 

I did configuration exactly like in the doc, but no luck. Moreover, before running the app I made a verification call via:

 

C:\prj\DEMO>netsh winhttp show proxy                                                                                                                                                                                                                                                                                                                                                                                Current WinHTTP proxy settings:                                                                                                                                                                                                                                                                                                                                                                                          Proxy Server(s) :  127.0.0.1:8888                                                                                                                                                                    Bypass List     :  (none) 

 

But the traffic between my app and Firefox still invisible in Fiddler even w/o any filters applied. What am I doing wrong with it?

[Nick Iliev]

Are you using localhost to test your Net Core application? If that is the case, then you could try to use the Fiddler aliases or NetBios machine name 

https://docs.telerik.com/fiddler/observe-traffic/troubleshooting/notraffictolocalhost 

[NIKOLAY]

Hi Nick,

 

After I changed my host name used in the browser for localhost.fiddler it started working. Thanks!

[NIKOLAY]

https://docs.telerik.com/fiddler/observe-traffic/troubleshooting/notraffictolocalhost

This link helped me; as soon as I used http://localhost.fiddler I began to see all https traffic FF <-> my core app. Thanks!