Troubleshoot Web Page Issues with HAR Files
Overview
A HTTP Archive (HAR) capture can help troubleshoot issues where a web page or a Meraki dashboard page does not work as expected in the browser. This includes pages that load only partway, remain blank, display incomplete content, respond slowly, or time out. It can also help when a specific dashboard element does not load or update correctly.
This article explains what a HAR file shows, when to use it instead of a packet capture, how to collect it in Google Chrome, and how to review it at a high level.
What is a HAR file
A HAR file records the interactions between a browser and a website or web application during page load. It includes browser-side HTTP requests and responses, HTTP status codes, timing data, and other page-load details.
HAR files are useful because most web traffic now uses Transport Layer Security (TLS) encryption. A packet capture can show network traffic on the wire, but it usually cannot show encrypted HTTP payloads. A HAR file helps fill that gap by showing what the browser receives and how the page behaves at the HTTP layer.
When to use a HAR capture
Use a HAR capture when the browser starts to load a page but the page does not fully load or does not behave correctly. Common examples include:
- A web page loads only part of its content
- A page remains blank after it starts loading
- A page stops loading partway through
- A dashboard page or element does not load or update correctly
- The dashboard UI is slow or times out during an action
In these cases, a HAR file can be more useful than a packet capture because it shows the HTTP transactions between the browser and the server.
When not to use a HAR capture
Do not use a HAR capture as the primary troubleshooting method if the browser shows any of the following errors:
- ERR_CONNECTION_REFUSED
- ERR_CONNECTION_RESET
- DNS-related errors
These errors usually mean the failure occurs before a full TLS session is established. In those cases, use a packet capture as the preferred troubleshooting method because the relevant point of failure is visible in network traffic rather than browser HTTP data.
How to take a HAR capture in Google Chrome
Start the HAR capture before reproducing the issue so it records the full page load.
- Open a new browser tab.
- Open Developer Tools by pressing
F12, or by selecting More Tools > Developer Tools in Chrome. - Select the Network tab.
- Confirm that recording is enabled and the indicator is red.
- Select Preserve log.
- Navigate to the web page or Meraki dashboard page you want to troubleshoot.
- Reproduce the issue and confirm that network activity appears in the Network pane.
- Select the export or download icon in the Network pane and save the HAR file.
HAR files can contain sensitive data. If Chrome shows an option to export a sanitized file or a file with sensitive data, share only the sanitized version with Meraki Support unless Meraki Support specifically requests otherwise.
If another browser is required, refer to that browser's documentation for HAR capture steps.
How to read and analyze a HAR capture
Google's HAR Analyzer can review the contents of a HAR file. Start by looking for failed requests, unexpected HTTP status codes, missing resources, long delays, or responses that differ between a working and non-working session.
For web page issues or dashboard UI issues, reviewing these items can help identify whether a browser request is failing, timing out, or returning incomplete data. If you are troubleshooting page-load, UI, slowness, or timeout issues with Meraki Support, HAR captures can assist with review.
Example case study
The HAR captures in this example were collected during troubleshooting for a Meraki Support case. Some information has been redacted to avoid disclosing customer information.
A user reports that the company website does not load on the office network. The same site loads when the user disconnects from office Wi-Fi and uses a carrier network instead.
Testing confirms the same result. The page appears blank on the office network, including over the office VPN, but it loads normally outside that network. Because the issue occurs after the page begins to load, HAR captures are taken in both the non-working (top) and working (bottom) scenarios for comparison.
The comparison shows that, in the failing case, the website returns 200 OK with no data. In the working case, the site returns the expected content. Because the traffic uses TLS and Cisco Meraki MX security and SD-WAN appliances do not inspect or modify TLS payloads, the issue points to the web server or application. The next step is to contact the site provider for further troubleshooting.