Securing Your Network with DNS over HTTPS (DoH) on OPNsense: A Comprehensive Guide

DNS over HTTPS (DoH) enhances your network's privacy and security by encrypting DNS queries. This guide provides a detailed walkthrough of configuring DoH on OPNsense, a robust and popular open-source firewall.

Why Use DNS over HTTPS?

Traditional DNS queries are sent in plain text, making them vulnerable to eavesdropping and manipulation. DoH encrypts these queries using HTTPS, protecting your DNS traffic from prying eyes. This offers several key benefits:

Increased Privacy: Prevents your ISP or other network observers from seeing which websites you visit.
Improved Security: Protects against DNS spoofing and other attacks that can redirect your traffic to malicious websites.
Enhanced Censorship Resistance: Makes it more difficult for entities to block access to specific websites by intercepting DNS queries.

Configuring DoH on OPNsense

OPNsense offers flexible options for implementing DoH. The most common approach involves using a DNS resolver that supports DoH, either directly within OPNsense or by configuring your clients to use a DoH-enabled resolver.

Method 1: Using a DoH-enabled Resolver in OPNsense

This method involves configuring OPNsense to act as a DNS server itself, forwarding queries to a DoH provider. This offers centralized control and simplifies management.

Install a DNS server package: OPNsense offers several DNS server packages, such as Unbound and BIND. Install and configure one of these.
Configure the DNS server for DoH: Most modern DNS servers allow configuration of DoH. You'll need to specify the DoH endpoint of your chosen provider (e.g., Cloudflare, Google Public DNS, Quad9). This usually involves adding a forwarder or specifying a custom configuration file depending on your chosen DNS server.
Configure OPNsense's network interfaces to use the DoH-enabled DNS server: In the OPNsense interface, set your LAN interface's DNS server to the IP address of your newly configured DNS server.
Verify the configuration: Use tools like dig +trace example.com to verify that your DNS queries are being sent over HTTPS.

Example using Unbound (configuration may vary slightly depending on version): You would need to configure Unbound's configuration file (often located at `/usr/local/etc/unbound.conf`) to include the DoH settings. This usually involves setting a `forward-zone` with the appropriate DoH address.


forward-zone:
    name: "example.com"
    forward-addr: 1.1.1.1
    forward-method: https

Method 2: Client-Side DoH Configuration

Alternatively, you can configure your individual clients (computers, smartphones, etc.) to use a DoH-enabled resolver. This requires less configuration on the OPNsense side but lacks centralized management.

Choose a DoH provider: Select a DoH provider like Cloudflare (1.1.1.1), Google Public DNS (8.8.8.8), or Quad9 (9.9.9.9).
Configure DoH on your clients: The process varies depending on the operating system and applications. For example, in most browsers, you can directly change the DNS settings.

Choosing a DoH Provider

Several reputable providers offer DoH services, each with its own privacy policy and features. Consider factors like privacy policy, performance, and security when making your selection.

Cloudflare (1.1.1.1): Popular choice known for its speed and privacy focus.
Google Public DNS (8.8.8.8): Widely used and generally reliable.
Quad9 (9.9.9.9): Focuses on security and blocking malicious domains.

Troubleshooting

If you encounter issues, check your OPNsense logs for errors. Ensure that your DNS server is correctly configured and reachable. Test your DoH configuration by verifying that your DNS queries are being encrypted using tools like tcpdump or network monitoring tools.

Conclusion

Implementing DoH on OPNsense significantly improves your network's privacy and security. By choosing the right method and provider, you can effectively protect your DNS traffic and enhance your overall online security posture. Remember to regularly review your configuration and update to the latest versions of your software for optimal performance and security.