Tailscale: Per-Device DNS & DoH Configuration For Enhanced Security

by Alex Johnson 68 views

Introduction

This article delves into the critical need for per-device DNS and DNS over HTTPS (DoH) configuration within Tailscale networks. Currently, Tailscale enforces a single, global DNS configuration across the entire tailnet. While this approach simplifies management, it overlooks the diverse needs and security requirements of individual devices. Implementing per-device DNS settings would significantly enhance privacy, security, and compatibility, enabling users to tailor their network configurations to suit specific use cases. This article explores the limitations of the current global DNS model and outlines the benefits of a more granular, device-centric approach.

The Need for Per-Device DNS / DoH

The current Tailscale setup applies DNS settings uniformly across the entire tailnet. This one-size-fits-all approach presents several challenges. Different devices have vastly different needs when it comes to DNS resolution. For instance, mobile devices may benefit from privacy-focused DoH resolvers to protect their data on public networks. Servers, on the other hand, might require internal resolvers or split DNS configurations to access corporate resources. By allowing per-device DNS configurations, users can strike a balance between privacy, security, and compatibility, ensuring that each device operates under the most appropriate settings.

Key Considerations:

  • Privacy: Mobile devices often connect to untrusted networks, making them vulnerable to DNS spoofing and eavesdropping. Using DoH can encrypt DNS queries, protecting user data from prying eyes.
  • Security: Servers often require access to internal resources and may need to use internal DNS resolvers. Enforcing a global DNS configuration can disrupt access to these resources and compromise server functionality.
  • Compatibility: Different devices may have different operating systems or software configurations that require specific DNS settings. A global DNS configuration may not be compatible with all devices, leading to connectivity issues.

Proposed Solution: Device-Specific DNS Configuration

To address these challenges, Tailscale should allow administrators to configure DNS settings on a per-device basis. This would involve several key changes to the Admin Console and API:

  1. Opt-in/out of MagicDNS: Allow each device to individually opt-in or opt-out of MagicDNS, providing greater control over DNS resolution.
  2. Custom DNS Servers/DoH URLs: Enable the specification of custom DNS servers or DoH URLs for each device, allowing administrators to tailor DNS settings to the specific needs of each device.
  3. Preserve Fallback Behavior: Ensure that devices can seamlessly switch between different networks without losing DNS resolution capabilities.

By implementing these changes, Tailscale can provide a more flexible and secure DNS configuration experience for its users.

Impact of Not Supporting Per-Device DNS / DoH in Tailscale

1. Security Gaps

Without per-device DoH, some devices inevitably fall back to unencrypted DNS, creating significant security vulnerabilities. This is particularly concerning for mobile devices that frequently connect to public Wi-Fi networks.

Impact:

  • DNS queries leak sensitive metadata on public or hostile networks, exposing user activity to potential eavesdroppers.
  • Devices that require encrypted DNS to meet their security baseline are unable to do so, compromising their security posture.
  • The absence of end-to-end privacy across the tailnet undermines the overall security of the network.

2. Mixed Environments Break

A single, global DNS setting simply cannot cater to the diverse needs of different device types in a mixed environment. This is a common scenario in many organizations, where servers, laptops, and mobile devices coexist on the same network.

Examples:

  • Servers often require internal resolvers for accessing corporate resources, while public DNS resolvers may not be sufficient.
  • Phones and laptops benefit from privacy-focused DoH resolvers like NextDNS, Cloudflare, or Quad9 to protect their data on untrusted networks.
  • Work devices may need to use corporate DNS servers to comply with company policies.
  • Devices used by children may require filtered DNS to block access to inappropriate content.

Impact:

  • Inevitably, something will break, leading to connectivity issues and user frustration.
  • Administrators may be forced to disable Tailscale DNS entirely on certain devices to maintain functionality, defeating the purpose of using Tailscale.
  • The tailnet becomes inconsistent and harder to manage, increasing the administrative burden.

3. Users Resort to Workarounds

In the absence of per-device DNS configuration, users are often forced to resort to various workarounds to achieve the desired DNS settings. These workarounds can be complex, fragile, and difficult to maintain.

Examples of workarounds include:

  • OS-level DoH overrides, which may not be supported on all operating systems.
  • Custom configurations for systemd-resolved, which require advanced technical knowledge.
  • Using NextDNS CLI agents, which can consume system resources and add complexity.
  • Local DNS proxies, which can introduce latency and increase the risk of misconfiguration.
  • Android Private DNS, which conflicts with MagicDNS and can lead to unexpected behavior.

Impact:

  • Fragile setups that are prone to breakage and require constant maintenance.
  • Difficult troubleshooting, as the root cause of DNS issues can be hard to diagnose.
  • DNS loops or partial outages, which can disrupt network connectivity.

4. Inconsistent Cross-Platform Experience

The current Tailscale setup can lead to an inconsistent DNS experience across different platforms. This is due to variations in operating system behavior and browser settings.

For example:

  • Android Private DNS conflicts with Tailscale DNS, leading to unpredictable behavior.
  • iOS cannot enforce DoH without VPN-provided settings, limiting privacy protection.
  • Browsers may switch resolvers automatically, bypassing the configured DNS settings.

Impact:

  • Different devices behave differently in the same tailnet, creating confusion and frustration.
  • DNS privacy varies unpredictably, undermining user trust in the security of the network.
  • Users lose trust in DNS consistency, making it difficult to rely on Tailscale for secure and reliable network connectivity.

5. Reduced Adoption in Security-Sensitive Environments

Organizations with strict security policies often require device-specific DNS rules to ensure compliance. The lack of per-device DNS configuration in Tailscale can be a major barrier to adoption in these environments.

Impact:

  • Some devices become non-compliant with security policies, creating potential risks.
  • Administrators may disable Tailscale DNS entirely to avoid compliance issues, limiting the functionality of Tailscale.
  • Organizations may avoid or limit Tailscale deployment altogether, opting for competing VPN solutions that offer per-client DNS configuration.

6. Compliance Risks

Devices that are required to use specific DNS configurations for compliance reasons cannot do so with a global DNS model. This includes devices that must use:

  • Encrypted DNS to protect sensitive data.
  • Logging DNS to track network activity.
  • Filtering DNS to block access to inappropriate content.
  • Department-mandated resolvers to comply with internal policies.

Impact:

  • Devices break policy, creating potential legal and financial liabilities.
  • Tailscale cannot be used in regulated environments, limiting its applicability.

Bottom Line

Not supporting per-device DNS/DoH locks Tailscale into a one-size-fits-all DNS model that weakens privacy, breaks mixed setups, forces workarounds, and limits adoption. Adding per-device DNS is essential as modern OSes and security requirements evolve.

Conclusion

Implementing per-device DNS and DoH configuration in Tailscale is not just a nice-to-have feature; it is a necessity for modern networks. The current global DNS model is inadequate for addressing the diverse needs and security requirements of individual devices. By allowing administrators to configure DNS settings on a per-device basis, Tailscale can enhance privacy, security, and compatibility, making it a more versatile and reliable VPN solution. As operating systems and security landscapes continue to evolve, the need for per-device DNS configuration will only become more critical. Tailscale must adapt to meet these changing demands to remain a competitive and trusted VPN provider.

For more information about DNS and network security, visit Cloudflare Learning Center.