Systemd-resolved: Securing Your DNS with DNS-over-HTTPS (DoH)

Systemd-resolved is a powerful and versatile network name resolver that's become a standard component in many Linux distributions. One of its key features is support for DNS-over-HTTPS (DoH), a protocol that enhances privacy and security when resolving domain names. This article delves into configuring and using DoH with systemd-resolved, explaining its benefits and potential challenges.

Understanding DNS-over-HTTPS (DoH)

Traditional DNS queries are sent over UDP or TCP, making them vulnerable to eavesdropping and manipulation. DoH encapsulates DNS queries within HTTPS requests, leveraging the security features of TLS to protect them. This means your DNS queries are encrypted, preventing your ISP or other network observers from seeing which websites you're accessing.

Key benefits of using DoH with systemd-resolved include:

• Enhanced Privacy: Protects your DNS queries from eavesdropping.
• Improved Security: Prevents DNS spoofing and other attacks.
• Censorship Resistance: Bypasses DNS censorship imposed by some networks.
• Simplified Configuration: Relatively easy to set up with systemd-resolved.

Configuring DoH with Systemd-resolved

Configuring systemd-resolved to use DoH is typically straightforward. The primary method involves modifying the `/etc/systemd/resolved.conf` file. However, the specific configuration options might vary slightly depending on your Linux distribution.

Here's a common approach:

1. Open the configuration file: Use a text editor with root privileges (e.g., `sudo nano /etc/systemd/resolved.conf`).
2. Add or modify the `DNS` option: This option specifies the DoH servers to use. Replace the placeholder with your desired DoH provider's URL. For example, to use Cloudflare's DoH service, you would add or modify this line: DNS=cloudflare-dns.com or DNS=https://cloudflare-dns.com/dns-query
3. (Optional) Set `DNSOverTLS` and `DNSOverHTTPS` options: Although usually implied by providing a DNS URL with `https://` , you can explicitly enable DoH by adding or uncommenting and setting the following options: DNSOverTLS=yes DNSOverHTTPS=yes
4. Save and reload systemd-resolved: After making the changes, save the file and reload systemd-resolved using the command: sudo systemctl restart systemd-resolved

Important Considerations:

• Choosing a DoH Provider: Select a reputable DoH provider that aligns with your privacy preferences. Popular options include Cloudflare (https://cloudflare-dns.com/dns-query), Google Public DNS (https://dns.google/dns-query), and Quad9 (https://dns.quad9.net/dns-query).
• Network Manager Integration: If you're using NetworkManager, you might need to configure DoH through its settings, which is distribution-specific.
• Firewall Rules: Ensure that your firewall allows outgoing connections on port 443 (HTTPS).
• Verification: After configuring DoH, you can verify it's working by using tools like dig +short myip.opendns.com @cloudflare-dns.com, replacing `cloudflare-dns.com` with your chosen DoH resolver

Troubleshooting DoH with Systemd-resolved

If you encounter issues, check the following:

• Systemd-resolved logs: Examine the systemd-resolved logs for error messages (e.g., using `journalctl -u systemd-resolved`).
• Firewall configuration: Ensure your firewall allows outbound connections on port 443.
• DNS server availability: Verify that the DoH server you're using is reachable.
• Network configuration: Ensure your network settings are correctly configured.

Conclusion

Using DoH with systemd-resolved provides a significant enhancement to the privacy and security of your DNS lookups. The configuration process is relatively straightforward, but troubleshooting may be necessary in certain cases. By carefully selecting a DoH provider and following the steps outlined above, you can effectively leverage the benefits of DoH for a more secure and private online experience.