Securing Your Debian System with DNS over HTTPS (DoH): A Comprehensive Guide

DNS over HTTPS (DoH) enhances your privacy and security by encrypting your DNS queries. This guide provides a detailed walkthrough of setting up DoH on your Debian system, covering various methods and considerations.

Understanding DNS over HTTPS

Traditional DNS queries are sent in plain text, making them vulnerable to eavesdropping and manipulation. DoH solves this by encrypting these queries using HTTPS, the same protocol used for secure web browsing. This prevents your ISP or other network observers from seeing which websites you're accessing.

Choosing a DoH Provider

Several reputable providers offer DoH services. Popular choices include:

• Cloudflare: https://cloudflare-dns.com/dns-query
• Google Public DNS: https://dns.google/dns-query
• Quad9: https://dns.quad9.net/dns-query
• NextDNS: (Requires account creation)

The best provider for you depends on your priorities. Consider factors like privacy policy, security features, and performance.

Methods for Configuring DoH on Debian

1. Using systemd-resolved (Recommended)

systemd-resolved is the recommended DNS resolver for Debian systems. It's integrated well with systemd and offers easy DoH configuration. First, ensure systemd-resolved is installed:

sudo apt update
sudo apt install systemd-resolved

Then, edit the /etc/systemd/resolved.conf file:

sudo nano /etc/systemd/resolved.conf

Add or modify the following lines, replacing the example with your chosen DoH provider:

DNS=https://cloudflare-dns.com/dns-query  # Replace with your provider
DNSOverTLS=yes

Save the file and restart systemd-resolved:

sudo systemctl restart systemd-resolved

Verify the configuration by checking the output of:

systemd-resolve --status

2. Modifying Network Manager

If you manage your network connections through NetworkManager, you can configure DoH within the settings of your connection profile. This method is often less convenient than using systemd-resolved.

3. Configuring individual applications

Some applications allow you to specify custom DNS servers directly within their settings. This is generally less effective than system-wide configuration, as it only affects that specific application.

Testing Your DoH Configuration

After configuring DoH, verify that your DNS queries are indeed being encrypted. Tools like curl can help you test this, although interpreting the results might require some technical understanding. Alternatively, you can use online tools designed to check DoH functionality.

Troubleshooting

If you encounter issues, check the following:

• Ensure that systemd-resolved is running correctly.
• Verify the DoH provider URL and that it's accessible.
• Check your firewall rules to ensure they don't block DoH traffic.
• Restart your network connection or reboot your system.

Conclusion

Implementing DoH on your Debian system is a straightforward process that significantly enhances your online privacy and security. By following these steps, you can effectively protect your DNS traffic from prying eyes. Remember to choose a reputable DoH provider that aligns with your privacy preferences and regularly review your security settings.