Troubleshooting DNS over HTTPS (DoH): Why Isn't It Working and How to Fix It

DNS over HTTPS (DoH) promises faster, more private DNS resolution. But sometimes, it just doesn't work as expected. This comprehensive guide will walk you through common reasons why DoH might be failing and offer solutions to get you back online securely.

Common Reasons Why DoH Isn't Working

• Incorrect Configuration: This is the most frequent cause. You might have entered the wrong DoH server address, failed to enable DoH in your browser or operating system settings, or have conflicting DNS settings.
• Network Restrictions: Firewalls, proxies, or network administrators might be blocking DoH traffic. Some corporate or school networks actively prevent the use of DoH for security reasons.
• DNS Server Issues: The DoH server you're using could be experiencing outages, maintenance, or have capacity problems. Switching to a different provider might solve the issue.
• Browser or OS Bugs: Rarely, bugs in your browser or operating system's DoH implementation can cause problems. Updating your software to the latest version often resolves this.
• Conflicting DNS Settings: If you have multiple DNS servers configured (e.g., both DoH and traditional DNS), they might be interfering with each other. Try disabling other DNS configurations temporarily.
• VPN or Proxy Interference: VPNs or proxies can sometimes interfere with DoH. Try temporarily disabling them to see if they're the cause.
• IPv6 Issues: Some DoH servers might not support IPv6 correctly. If you're using IPv6, try switching to IPv4 temporarily.
• DNSSEC Validation Problems: If DNSSEC is enabled and there's a problem with the DNSSEC chain of trust, it might prevent DoH from working correctly.

Troubleshooting Steps

1. Verify DoH Configuration:

Check your browser's settings to ensure DoH is correctly enabled and that the correct server address is specified. Common DoH providers include Cloudflare (https://cloudflare-dns.com/dns-query), Google Public DNS (https://dns.google/dns-query), and Quad9 (https://dns.quad9.net/dns-query). The exact location of these settings varies depending on the browser and operating system.

2. Check Network Connectivity:

Ensure you have a stable internet connection. Try accessing other websites to rule out a broader internet connectivity issue. If you're on a corporate or school network, check with your network administrator to confirm that DoH is allowed.

3. Test with a Different DoH Provider:

If you're using one DoH provider, try switching to another (e.g., Cloudflare, Google, or Quad9) to see if the problem is specific to the provider you were using.

4. Temporarily Disable Firewalls, VPNs, and Proxies:

Disable any firewalls, VPNs, or proxies temporarily to determine if they are interfering with DoH traffic. Re-enable them one at a time to pinpoint the culprit.

5. Check for Browser or OS Updates:

Update your web browser and operating system to the latest versions. Bug fixes in these updates might resolve DoH related problems.

6. Check DNS Settings in Your Operating System:

Ensure that no conflicting DNS configurations exist in your operating system's network settings. If you have manually set DNS servers, try setting them to automatically obtain DNS server addresses.

7. Inspect Browser Console for Errors:

Open your browser's developer tools (usually by pressing F12) and check the console for any errors related to DNS resolution or network requests. These errors can provide valuable clues about the root cause.

8. Consider Using a DoH Client:

If all else fails, consider using a dedicated DoH client application. These applications often provide more granular control over DoH settings and may bypass some browser or operating system limitations.

Advanced Troubleshooting

If you've tried the above steps and DoH is still not working, you might need to perform more advanced troubleshooting such as checking your network configuration files (e.g., `/etc/resolv.conf` on Linux), using network diagnostic tools like `ping` and `traceroute`, or consulting your network administrator or internet service provider.

Remember to always exercise caution when modifying network settings. Incorrect configurations can disrupt your internet access. If you're unsure about any of these steps, consult a professional.