What Is DNS Port? Understanding Port 53 and DNS Protocols

Which Port Does DNS Use?

DNS primarily uses port 53 for standard queries. However, modern DNS also supports encrypted protocols that use different ports:

Protocol	Port Number	Usage
UDP	53	Standard DNS queries (most lookups)
TCP	53	Zone transfers, large responses, DNSSEC data
DoH (DNS over HTTPS)	443	Encrypted DNS using HTTPS
DoT (DNS over TLS)	853	Encrypted DNS over TLS connection

Key Entities: UDP, TCP, Port 53, DNSSEC, DoH, DoT, IANA, ICANN, Firewall, DNS Resolver

Why DNS Uses Port 53

DNS was standardized in IETF RFC 1035, which designated port 53 for DNS traffic. This port was chosen because:

It was free at the time of assignment (early Internet design)
It supports both UDP and TCP for flexible communication
It allows firewalls and routers to easily identify and route DNS traffic

All major DNS servers and resolvers—such as Google DNS (8.8.8.8), Cloudflare (1.1.1.1), and Quad9 (9.9.9.9)—listen on port 53 for incoming queries.

Historical Note: Port 53 was officially assigned to DNS by IANA (Internet Assigned Numbers Authority) in the early 1980s.

UDP vs TCP in DNS

DNS can operate over both UDP and TCP, and each protocol serves a specific purpose:

UDP (Default Mode)

✓ Used for quick, lightweight lookups
✓ Each query is a small packet (≤512 bytes)
✓ Faster, lower latency
✗ Not encrypted by default

TCP (Fallback / Extended Use)

✓ Used when DNS response >512 bytes
✓ Also used for zone transfers (AXFR)
✓ Reliable but slightly slower
✓ Supports DNSSEC validation

Example:

A normal query for example.com A record → UDP 53

A full zone transfer from ns1.example.com → TCP 53

Secure DNS Ports

Modern DNS protocols use encryption to protect privacy and prevent attacks. These protocols use different ports:

Protocol	Port	Description
DNS over HTTPS (DoH)	443	Encrypts DNS inside HTTPS traffic
DNS over TLS (DoT)	853	Encrypts DNS at transport layer
DNSCrypt	443 / 8443	Alternative encryption protocol

These protocols prevent:

DNS Spoofing

Prevents hijacking of DNS responses

ISP Surveillance

Hides DNS queries from ISPs

MITM Attacks

Prevents man-in-the-middle attacks

Privacy-focused DNS providers: Cloudflare (1.1.1.1), NextDNS, Quad9 (9.9.9.9)

DNS Port and Firewalls

Many networks restrict or inspect DNS traffic. Firewalls must allow port 53 for devices to perform lookups. If it's blocked, domain names won't resolve, even if IP connections work.

Firewall Configuration Example (Linux)

sudo ufw allow 53/udp
sudo ufw allow 53/tcp

💡 Pro Tip: For privacy-focused setups, you can redirect DNS queries through DoH (443) or DoT (853) to bypass filtering.

How to Test DNS Port Connectivity

You can test if port 53 is accessible using various command-line tools:

Using nslookup

nslookup dnslookup.pro 8.8.8.8

Using dig

dig @1.1.1.1 example.com +tcp

Using telnet (to test port availability)

telnet 8.8.8.8 53

If you receive a valid DNS response, port 53 is open and functioning correctly.

Or use the DNS Lookup Tool

Verify real-time resolver connections with our online tool:

DNS Lookup Tool

DNS Port Security Risks

While port 53 is essential for DNS, it can be vulnerable to various security threats:

Port Hijacking

Attackers may redirect DNS queries to rogue servers

DNS Amplification Attacks

Used in DDoS attacks via open port 53 resolvers

Data Exfiltration

Malware uses DNS tunnels on port 53 to steal data

Prevention Measures:

✓

Restrict External Port 53 Access

Only allow trusted sources to query your DNS servers

✓

Enable DNSSEC

Ensures data integrity and authenticity of DNS responses

✓

Use Encrypted DNS (DoH / DoT)

Protects DNS queries from interception and manipulation

✓

Implement Rate Limiting

Prevents DNS amplification attacks

Common DNS Ports Summary

Function	Port	Protocol
Standard DNS Queries	53	UDP / TCP
Secure DNS over TLS	853	TCP
DNS over HTTPS	443	HTTPS
Zone Transfer (AXFR)	53	TCP
Alternate (DNSCrypt)	443 / 8443	TCP / UDP

Key Entities Related to DNS Ports

ICANN / IANA

Assign official port numbers

Cloudflare DNS (1.1.1.1)

Fast, encrypted DNS resolver

Google DNS (8.8.8.8)

Global resolver using port 53

Quad9 (9.9.9.9)

Security-focused resolver using DNS over TLS

DNSSEC

Works over both UDP and TCP 53 for validation

TLS 1.3

Encryption protocol for DoT

Frequently Asked Questions

1. What port does DNS use?

DNS uses port 53 for both UDP and TCP traffic.

2. Why does DNS need both TCP and UDP?

UDP is faster for small queries; TCP ensures reliability for large responses and zone transfers.

3. Can DNS use other ports?

By default, no — though encrypted variants use 443 (DoH) or 853 (DoT).

4. Is port 53 safe?

Yes, but it's vulnerable if left open to the Internet without rate limits.

5. How can I secure my DNS port?

Use firewalls, encrypted DNS protocols, and block external port 53 queries on non-DNS servers.

What Is DNS Port?