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

DNS over HTTPS (DoH) enhances your online privacy and security by encrypting your DNS queries. Instead of sending your DNS requests in plain text (which can be intercepted and analyzed), DoH encrypts them using HTTPS, making them much harder to eavesdrop on. This guide provides a detailed walkthrough of setting up DoH on various Linux distributions.

Why Use DNS over HTTPS?

• Enhanced Privacy: Prevents your ISP and other potential eavesdroppers from seeing which websites you visit.
• Improved Security: Protects against DNS spoofing and other attacks that target the DNS resolution process.
• Increased Censorship Resistance: Makes it harder for networks to block access to specific websites by manipulating DNS results.
• Faster Resolution (Potentially): Some DoH providers offer faster resolution times due to optimized infrastructure.

Choosing a DoH Provider

Selecting a reputable DoH provider is crucial. Consider factors like privacy policy, location, and performance. Popular options include:

• Cloudflare (1.1.1.1): Known for its speed and privacy focus.
• Google Public DNS (8.8.8.8): A widely used and generally reliable option.
• Quad9 (9.9.9.9): Focuses on security and blocking malicious domains.
• NextDNS: Offers advanced customization and filtering options.

Setting Up DoH on Different Linux Distributions

Systemd-resolved (Most Modern Distributions)

Many modern Linux distributions use systemd-resolved as their DNS resolver. This is often the easiest method to configure DoH. You'll typically edit the /etc/systemd/resolved.conf file. Add or modify the following lines, replacing with your chosen provider's address:

[Resolve] 
DNS= 
DNSOverHTTPS=yes

For example, for Cloudflare:

[Resolve]
DNS=cloudflare-dns.com
DNSOverHTTPS=yes

After saving the file, restart systemd-resolved:

sudo systemctl restart systemd-resolved

NetworkManager

If you're using NetworkManager, you can configure DoH through its GUI or command-line tools. The exact steps vary depending on your desktop environment. Consult your distribution's documentation for specific instructions.

Network Configuration Files (e.g., /etc/resolv.conf)

Directly editing /etc/resolv.conf is generally discouraged as it's often managed dynamically. Modifying it might lead to conflicts. However, some distributions allow you to set DNS settings in other network configuration files (e.g., files within /etc/netplan/).

Using a Different DNS Client (e.g., unbound)

For advanced users, using a DNS client like unbound provides more control and customization options. You'll need to configure unbound to use DoH and then configure your system to use unbound as its DNS resolver. This involves more complex configuration steps and is beyond the scope of this basic guide.

Verifying DoH is Working

After configuring DoH, you can verify it's working by using tools like dig or nslookup. These tools can show you the DNS query method being used.

dig @ example.com +trace

If DoH is working correctly, you should see HTTPS in the output indicating that your DNS query was made using DoH. Note that the exact output may vary depending on the tool and the DNS provider.

Troubleshooting

If you encounter issues, check your network configuration, ensure your chosen DoH server is reachable, and review your configuration files for any errors. Consult your distribution's documentation for more specific troubleshooting steps.

Setting up DNS over HTTPS significantly improves the security and privacy of your Linux system. By following these steps and choosing a reliable provider, you can protect your online activity from unwanted surveillance.