Fiddler not capturing traffic

[Boone]

I've been using Fiddler for years, but the most recent version I've installed (v4.4.8.4) no longer captures any traffic.

- The Filters are turned off (and using the "Troubleshoot Filters" doesn't appear to change anything)
- Traffic does not appear in Fiddler when I visit http://ipv4.fiddler:8888
- However, traffic *does* appear when I visit http://localhost:8888

Does anyone have a suggestion?

Thanks.

[Eric Lawrence]

Hello, Boon--

The symptoms described indicate that Fiddler is listening properly and it isn't blocked by a firewall. However, they also suggest that your system's proxy settings are not getting set correctly.

You can manually look at your proxy settings by clicking Tools > WinINET Options > LAN Settings while Fiddler is "Capturing". These should be pointed at 127.0.0.1:8888 but based on your description, they probably aren't.

There are a few possibilities:

1> You are on a corporate network where the IT Administrator has used Group Policy to enforce a particular proxy. The WinINET options will typically show a yellow banner if that's the case.

2> You have some other software installed which is interfering with the system proxy setting. Some security software or VPN software will constantly overwrite the proxy settings.

3> Your system has some configuration problem where the proxy settings are not properly being persisted. You can try setting the proxy setting to address 127.0.0.1 and port 8888 yourself, click "Ok" and see if the settings "stick."

Regards,
Eric Lawrence
Telerik

 

 

[Boone]

Yes, I think you identified it perfectly. It appears that my company is setting specific proxy settings that I cannot override.

FWIW, the only workaround that I was able to find was to run Chrome (my browser of choice) with a command-line option of: --proxy-server=127.0.0.1:8888

This forces a proxy for that instance of Chrome and lets me start capturing Fiddler traffic again.

[Eric Lawrence]

Hi, Boone--

Yes, if Group Policy is in use, the IE proxy settings are "locked" from modification by normal users. If you are an admin on your PC (a user with Administrative Group permissions) you can right-click Fiddler and choose "Run as Administrator." When you do this, Fiddler should be able to (temporarily) overwrite the system's proxy settings.

As you noted, Chrome (as well as Firefox) can have their proxy settings manually adjusted independently from the system settings.

Regards,
Eric Lawrence
Telerik

 

 

[Boone]

I appreciate the suggestion, but that didn't seem to work for me.

I am an administrator on my PC. However, even if I run Fiddler as an administrator, the proxy settings don't persist.

At least I seem to have a workaround with using the Chrome command-line options. It's not perfect, but it looks like my Group Policy might not give me a better option.

Thanks

[SeethaRaam]

Hi Eric,

I too have a similar problem. My IE proxy settings are not locked and i see that  the proxy is correctly configured to  to 127.0.0.1 and port is 8888. I also tried running Fiddler as Administrator but no luck.

Can you let me know how we can find out whether some security software or VPN software is interfering with my system proxy setting.

thanks in advance.

-Sita Ram

 

 

[Alexander]

Hi,

What do you mean by "similar problem"? Fiddler is not capturing any traffic?

"Can you let me know how we can find out whether some security software or VPN software is interfering with my system proxy setting."

Since the proxy settings are the correct one, then it seems that there is no such software installed on your machine.

Regards,
Alexander
Telerik

[Sreenath]

I have correct configurations (127.0.0.1 and port 8888) and followed everything based on the link https://www.telerik.com/blogs/configuring-firefox-for-fiddler

But still FireFox is not capturing the JS. It works perfectly fine in IE and Chrome but not in FireFox. Is there any thing else need to check?

[Alexander]

Hi Sreenath,

If you are not seeing the traffic from Firefox in Fiddler then it has to be configuration problem. What proxy settings did you set in Firefox? Some screenshots at Firefox's configuration would be great.

Regards,
Alexander
Telerik

[Prashansa]

Hi Admin, '

I am using aproxy server for the LAN and when the proxy settings are enabled and I try to capture traffic from fiddler I am getting the below error:

 

[Fiddler] The connection to '10.***.***.*1' failed.
Error: TimedOut (0x274c).
System.Net.Sockets.SocketException A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 10.***.***.*1:80

 

I am not sure how I can use a proxy along with the fiddler. Kindly suggest. Looking forward for your reply.

[Simeon]

Hello Prashansa,

By default, Fiddler 'chains' to the WinINET (Internet Explorer) proxy on startup. If your LAN proxy server is not configured as WinINET proxy, you could configure the upstream proxy of Fiddler manually. In order to do this, please click Tools\Options... from the Fiddler menu and then open the Gateway tab. Select the Manual Proxy Configuration option and enter the address of your proxy into the field.

Regards,
Simeon
Progress Telerik

[John]

I'm having similar problems capturing HTTP traffic.

Environment:  Windows 7 Version 6.1 (Build7601: Service Pack 1)

Proxy Settings:  

file:  proxy settings.jpg

I'm using  Chrome (Version 75.0.3770.142 (Official Build) (64-bit)),

From within Chrome, the proxy settings references the same dialog noted above

This must be something really simple. . .

 

 

 

[John]

I should add that trying to access a site over port 8888 gives me a timeout

[John]

[Fiddler] The connection to 'matterhorn.metaswitch.com' failed. 
Error: TimedOut (0x274c). 
System.Net.Sockets.SocketException A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 192.91.191.185:8888

[Eric R | Senior Technical Support Engineer]

Hi John,

One way to test if Fiddler is listening correctly is to navigate to localhost:8888 on the local machine. This will return the Fiddler Echo Service. 



Although, accessing other sites over the same port will result in a timeout because these sites wouldn't be using the same external port. Additionally, accessing a remote machine which is running Fiddler using the external IP and port may not work unless the Allow remote computers to connect configuration is set.



I hope this helps. Please let me know if you need any additional information. Thank you.

Regards,

Eric R | Technical Support Engineer
Progress Telerik