What is DNS over TLS (DoT)?

DNS over TLS (DoT) is a security protocol that encrypts DNS queries using the Transport Layer Security (TLS) protocol. It was designed to improve privacy and security by preventing DNS requests from being monitored, intercepted, or tampered with by unauthorized parties.

By encrypting the communication between a user’s device and the DNS resolver, DoT helps protect DNS traffic from surveillance, censorship, and man-in-the-middle attacks. Unlike traditional DNS, which transmits queries in plaintext, DoT ensures that DNS requests remain confidential while in transit.

DoT operates at the transport layer of the OSI model, providing encryption similar to the way TLS secures websites via HTTPS.

How DNS Over TLS Works

DNS over TLS works by wrapping standard DNS queries within a TLS-encrypted tunnel. This encryption process secures the DNS traffic as it travels between the client and the DNS resolver, shielding it from eavesdropping and manipulation.

Key technical characteristics:

• Default Port: DoT runs on port 853 by default.
  
  
• Encryption: DNS queries are encrypted with TLS, akin to how HTTPS encrypts website traffic.
  
  
• Protocol: DoT uses Transmission Control Protocol (TCP), whereas traditional DNS typically uses User Datagram Protocol (UDP) for faster, but unsecured, communication.
  
  
• Process: A secure TLS handshake occurs before any DNS data is exchanged, ensuring both privacy and data integrity.

By establishing a secure channel first, DoT ensures that all DNS queries and responses are protected from interception or spoofing attempts.

Why Use DNS Over TLS?

Organizations and individuals choose DoT for several privacy and security benefits:

• Protection Against Eavesdropping: Encrypting DNS queries prevents ISPs, network administrators, or attackers from seeing which websites users are querying.
  
  
• Defense Against Spoofing: DoT helps thwart DNS spoofing attacks that could redirect users to malicious websites.
  
  
• System-Wide Encryption: Unlike browser-based protections, DoT can encrypt all DNS traffic from a device, regardless of which application is generating the query.
  
  
• Enhanced Privacy: DoT hides DNS activity from unauthorized observers, contributing to a more private internet experience.

Compare: DoT vs DoH and Other DNS Encryption Protocols

As organizations and individuals seek better privacy and security, multiple protocols have emerged to encrypt DNS traffic. While DNS over TLS (DoT) is a widely supported option, it is not the only method available. Protocols like DNS over HTTPS (DoH), DNSCrypt, and DNS-over-QUIC (DoQ) each offer different approaches to securing DNS queries, with variations in performance, privacy benefits, and deployment flexibility.

Understanding these differences helps clarify when to use DoT versus alternatives. Here’s a comparative overview:

For an in-depth comparison, see our guide on DNS over TLS vs DNS over HTTPS.

DNS over TLS Port and Configuration

The default port for DoT is 853, which distinguishes it from standard DNS traffic and encrypted web traffic on port 443.

To implement DoT:

• Ensure your DNS resolver supports DoT (e.g., DNSFilter).
  
  
• Configure TLS certificate verification to establish a trusted connection.
  
  
• Apply DoT settings at the system level or on network equipment like routers and firewalls.
  
  
• Some operating systems and enterprise solutions may support DoT natively or through dedicated agents.

For configuration help, check our guide on encrypting DNS with DoT.

Limitations of DoT

While DoT significantly enhances privacy, it has some limitations:

• Limited Device and Network Support: Not all devices, routers, or networks support DoT natively.
  
  
• Easier to Block or Throttle: Since DoT uses a distinct port (853), network administrators or firewalls can more easily block or restrict it compared to DoH, which blends with standard HTTPS traffic.
• Requires System-Level Access: Setting up DoT often requires admin access to devices or network infrastructure, which may not be feasible in all environments.

Examples of DNS over TLS

• DNSFilter uses DoT as its default method of DNS encryption, protecting DNS queries in transit across networks and devices.
  
  
• Enterprises enforce DoT across their workforce devices to ensure consistent, encrypted DNS resolution at the system level, enhancing both privacy and security in hybrid and remote work environments.

Who Might Use DoT?

• Managed Service Providers (MSPs) managing endpoint security across diverse client environments.
  
  
• Privacy-conscious individuals who want device-wide DNS encryption.
  
  
• Enterprise IT teams that need to secure DNS queries across all applications and services, not just browser traffic.

Related Terms

• DNSSEC: Verifies the authenticity of DNS responses to prevent tampering.
• DNS: The foundational system for translating domain names into IP addresses.
• PDNS (Protective DNS): A security strategy that combines DNS resolution with threat intelligence to detect and prevent cyberattacks.
• DNS over HTTPS (DoH): Encrypts DNS queries within HTTPS connections.
• DNS Poisoning: An attack technique where false DNS information is inserted into a resolver’s cache.
• DNS Filtering: Security and policy enforcement method that blocks access to harmful, suspicious, or non-compliant domains at the DNS layer.

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