Port 53 (DNS)
Port 53 is DNS, the service that turns names like example.com into IP addresses. Your device sends queries to a resolver on port 53, and resolvers ask authoritative name servers on the same port.
- Service
- DNS
- Protocol
- TCP and UDPBoth. Ordinary queries go over UDP; TCP is used when an answer is too large for UDP, for zone transfers, and by resolvers that retry over TCP.
- IANA registry
- Officially assigned: domain (Domain Name Server), TCP/UDP
Check if a port is open on your IP
We only check the address you are visiting from, one TCP port at a time. You cannot enter someone else’s address: this is not a port scanner.
Is it safe to open port 53?
An authoritative server for your own domains needs port 53 open. A resolver that answers anyone on the internet (an open resolver) gets abused in DNS amplification attacks, as CISA warns; restrict recursion to your own networks.
Sources
“Port 53 is already in use”: how to fix it
The error means another program is already listening on port 53. Find its process ID (PID), then stop that program or start yours on a different port.
Windows (Command Prompt or PowerShell as administrator)
netstat -ano | findstr :53taskkill /PID <PID> /FmacOS
lsof -nP -iTCP:53 -sTCP:LISTENkill <PID>Linux
sudo ss -ltnp | grep :53sudo lsof -i :53sudo kill <PID>Replace <PID> with the number from the last column (Windows) or the PID column (macOS, Linux).
Why a port can look closed when your server is running
Most home networks sit behind a router doing NAT: the router owns the public address, and your computer has a private one such as 192.168.1.10. A connection from the internet reaches the router and stops there unless you add a port forwarding rule to your computer.
Many mobile and some home providers go further and use carrier-grade NAT (CGNAT): several customers share one public address, and your router itself gets an address from 100.64.0.0/10. Then no rule on your side can open a port; ask the provider for a public IP or use a tunnel or VPN service.
Even with forwarding in place, the firewall on the computer (Windows Defender Firewall, ufw, firewalld) must allow the port, and the program must listen on all interfaces (0.0.0.0), not only on 127.0.0.1.
UDP cannot be checked this way: a UDP service usually stays silent to packets it does not understand, so “no answer” means nothing. This check uses TCP only.
Frequently asked questions
What is port 53 used for?
Port 53 is DNS, the service that turns names like example.com into IP addresses. Your device sends queries to a resolver on port 53, and resolvers ask authoritative name servers on the same port.
Is port 53 TCP or UDP?
Both. Ordinary queries go over UDP; TCP is used when an answer is too large for UDP, for zone transfers, and by resolvers that retry over TCP.
Is it safe to open port 53?
An authoritative server for your own domains needs port 53 open. A resolver that answers anyone on the internet (an open resolver) gets abused in DNS amplification attacks, as CISA warns; restrict recursion to your own networks.
How do I free port 53 if it is already in use?
Find the process: on Windows run netstat -ano | findstr :53 and stop it with taskkill /PID <pid> /F; on macOS or Linux run lsof -i :53 and stop it with kill <pid>.