How to collect a network trace

If you come across an issue, a network trace can sometimes provide much helpful information. This how-to guide shows you the options to collect a network trace.

Fiddler is a powerful tool for collecting HTTP traces. Install it from telerik.com/fiddler, launch it, and then run your app and reproduce the issue. Fiddler is available for Windows, macOS, and Linux.

If you connect using HTTPS, there are some extra steps to ensure Fiddler can decrypt the HTTPS traffic. For more information, see the Fiddler documentation.

Once you collect the trace, you can export the trace by choosing File > Save > All Sessions from the menu bar.

This method works for all apps.

You can collect raw TCP traces using tcpdump by running the following command from a command shell. You may need to be root or prefix the command with sudo if you get a permissions error:

tcpdump -i [interface] -w trace.pcap

Replace [interface] with the network interface you wish to capture on. Usually, this is something like /dev/eth0 (for your standard Ethernet interface) or /dev/lo0 (for localhost traffic). For more information, see the tcpdump man page on your host system.

man tcpdump

Most browser Developer Tools have a "Network" tab that allows you to capture network activity between the browser and the server.

1. Open the DevTools

   • Select F12
   • Select Ctrl+Shift+I (Windows/Linux) or Command+Option+I (macOS)
   • Select Settings and more and then More Tools > Developer Tools

2. Select the Network Tab

3. Refresh the page (if needed) and reproduce the problem

4. Select the Export HAR... in the toolbar to export the trace as a "HAR" file