Securing Your Network with DNS over HTTPS on FortiGate: A Comprehensive Guide

DNS over HTTPS (DoH) is a protocol that encrypts Domain Name System (DNS) lookups, enhancing user privacy and security. FortiGate firewalls, known for their robust security features, offer various ways to implement and manage DoH, providing granular control and visibility. This guide will walk you through the process, addressing common challenges and best practices.

Understanding the Benefits of DoH

Implementing DoH on your FortiGate firewall offers several key advantages:

• Enhanced Privacy: DoH encrypts DNS queries, preventing eavesdropping on network traffic and masking your browsing activity from your ISP and potential intruders.
• Improved Security: Encryption protects against DNS spoofing and cache poisoning attacks, which can redirect users to malicious websites.
• Centralized Management: FortiGate allows you to centrally manage DoH settings, ensuring consistent security policies across your entire network.
• Granular Control: You can configure specific DoH servers and apply policies based on user groups, devices, or applications.
• Integration with Existing Infrastructure: DoH integrates seamlessly with FortiGate's existing security features, providing a holistic security solution.

Implementing DoH on FortiGate: Different Approaches

FortiGate offers flexibility in implementing DoH. The optimal approach depends on your specific network configuration and security requirements. Key methods include:

1. Utilizing a FortiGate-Managed DoH Server:

FortiGate itself doesn't inherently offer a built-in DoH server. Instead, it can act as a proxy, forwarding requests to a chosen third-party DoH server (like Google Public DNS over HTTPS, Cloudflare's 1.1.1.1, or Quad9). This allows you to benefit from DoH while retaining control over the DNS resolver used.

Configuration Steps (general outline, specifics vary by FortiGate version):

1. Configure a custom DNS server profile specifying the DoH server's address and port (usually 443).
2. Apply the DNS server profile to relevant interfaces or security policies.
3. Monitor logs for any issues or anomalies.

2. Client-Side DoH Configuration:

Allowing clients to directly connect to DoH servers provides more granular control at the endpoint. However, this may reduce the overall network visibility compared to FortiGate-managed DoH.

This approach usually requires configuring individual devices (computers, smartphones) to use a preferred DoH resolver. FortiGate doesn't directly manage this configuration.

3. Hybrid Approach:

A hybrid approach combining both methods offers a balance between centralized control and client flexibility. For example, you can mandate DoH for specific user groups or devices through FortiGate while allowing others to use their client-side DoH configurations.

Troubleshooting Common Issues

You might encounter issues like DNS resolution failures or slow speeds. Here are some troubleshooting tips:

• Verify DoH Server Address and Port: Ensure the address and port are correctly configured in the FortiGate's DNS server profile.
• Check Network Connectivity: Confirm network connectivity to the selected DoH server.
• Examine FortiGate Logs: Review the FortiGate logs for any errors related to DNS resolution or DoH.
• Test with Different DoH Servers: If issues persist, try a different public DoH server.
• Review Firewall Rules: Ensure that firewall rules don't block DoH traffic (port 443).

Security Considerations and Best Practices

While DoH enhances privacy and security, remember these aspects:

• Choose a Reputable DoH Provider: Select a DoH provider with a strong reputation for security and privacy.
• Monitor DNS Traffic: Even with DoH, monitoring DNS traffic for suspicious activity is crucial. FortiGate's logging and monitoring capabilities are essential here.
• Consider DNSSEC: Implement DNSSEC (DNS Security Extensions) to further protect against DNS spoofing and other attacks.
• Regular Updates: Keep your FortiGate firmware and DoH provider’s infrastructure up-to-date with security patches.

By carefully planning and implementing DoH on your FortiGate firewall, you can significantly improve your network's security and privacy posture. Remember to consult FortiGate's official documentation for the most accurate and up-to-date configuration instructions based on your specific FortiGate model and firmware version.