FortiGate and DNS over HTTPS (DoH): A Comprehensive Guide

DNS over HTTPS (DoH) is a method that encrypts DNS queries, enhancing user privacy and security. This guide explores how DoH works, its benefits and drawbacks, and how to configure and manage it with FortiGate firewalls.

Understanding DNS over HTTPS (DoH)

Traditional DNS queries are sent in plain text, making them vulnerable to eavesdropping and manipulation. DoH addresses this by encrypting these queries using HTTPS, the same protocol used for secure web browsing. This encryption protects the DNS queries from prying eyes, preventing third parties from seeing which websites you are accessing.

DoH typically utilizes port 443, the standard port for HTTPS. This allows it to often bypass firewalls and other network security measures that might block traditional DNS traffic on port 53.

Benefits of Using DoH with FortiGate

• Enhanced Privacy: DoH protects your DNS queries from interception, shielding your browsing activity from your ISP, potential attackers, and even your own network administrator (depending on configuration).
• Improved Security: Encryption prevents DNS spoofing and other attacks that could redirect you to malicious websites.
• Bypass Censorship: In some regions, DoH can help bypass government or organizational censorship of websites.
• Simplified Management (with FortiGate): FortiGate offers centralized management capabilities, allowing you to easily configure and monitor DoH settings across your network.

Drawbacks of DoH

• Reduced Visibility for Network Administrators: DoH can make it harder for network administrators to monitor DNS traffic and identify potential security threats.
• Potential for Misuse: While beneficial for privacy, DoH can also be used to mask malicious activity.
• Compatibility Issues: Older devices or applications may not support DoH.
• Performance Overhead: While generally minimal, DoH can introduce some slight performance overhead compared to traditional DNS.

Configuring DoH on FortiGate

FortiGate's support for DoH involves several aspects, primarily focusing on controlling client access and potentially acting as a DoH proxy itself. Specific configuration steps depend heavily on your FortiGate version and desired setup. Generally, the approach involves configuring DNS settings on the FortiGate and potentially deploying policies to manage client access to external DoH resolvers or internally deployed DoH resolvers. The specifics are detailed in the FortiGate documentation for your specific model and firmware version.

Key aspects of FortiGate DoH configuration often include:

• Defining DNS Servers: Specifying the DoH server addresses (e.g., Google Public DNS over HTTPS, Cloudflare DoH) or your own internal DoH server.
• Creating Security Policies: Establishing firewall rules to allow or block DoH traffic. This is crucial for controlling which clients can use DoH.
• Monitoring and Logging: Implementing logging and monitoring to track DoH usage and identify potential problems.

Using a FortiGate as a DoH Proxy

While less common than using external DoH providers, you can configure your FortiGate to act as a DoH proxy. This allows for greater control and visibility. You would need to configure the FortiGate with a DoH server role and appropriately manage access through policies. Consult the FortiGate documentation for detailed instructions on setting up this more advanced configuration.

Troubleshooting DoH with FortiGate

If you encounter problems with DoH, check the following:

• Firewall Rules: Ensure that your firewall rules allow DoH traffic (typically on port 443).
• DNS Server Configuration: Verify that the DoH server addresses are correctly configured.
• Client Configuration: Check that your clients are configured to use DoH and are pointing to the correct server.
• FortiGate Logs: Examine FortiGate logs for any errors or warnings related to DoH.

Remember to always refer to the official FortiGate documentation for the most accurate and up-to-date configuration instructions.