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Port 53: DNS

Port 53 (TCP/UDP) is used by DNS. Expose it only when required, with encryption and strong authentication, ideally limited to known IP addresses.

Updated

Port53
ProtocolTCP/UDP
ServiceDNS
Internet exposureOpen only if you need it

Check if port 53 is open

What is port 53 used for?

Domain Name System lookups. Queries normally use UDP; large responses and zone transfers use TCP.

Should port 53 be open?

Open only if you need it. Expose it only when required, with encryption and strong authentication, ideally limited to known IP addresses. Only authoritative DNS servers should answer the public internet. An open recursive resolver gets abused for DDoS amplification. The Port Checker tests the TCP side only.

See what is listening on port 53

# Linux
sudo ss -tlnp | grep ':53 '

# macOS
sudo lsof -nP -i TCP:53 -sTCP:LISTEN

# Windows (PowerShell)
Get-NetTCPConnection -LocalPort 53 -State Listen

Open or block port 53 in a firewall

# Ubuntu / Debian (ufw)
sudo ufw allow 53
sudo ufw deny 53

# Windows (PowerShell, as administrator)
New-NetFirewallRule -DisplayName "Port 53" -Direction Inbound -Protocol TCP -LocalPort 53 -Action Allow

On cloud servers, also open the port in the provider’s security group or network firewall. At home, a service behind a router needs a port-forwarding rule to the device’s local IP.

Test it from outside

A port can be open on the server but blocked upstream. The Port Checker connects from the internet, so it shows what the world sees. From your own machine, use nc -vz example.com 53 (macOS/Linux) or Test-NetConnection example.com -Port 53 (Windows).

Port CheckerTest whether a server accepts connections on specific ports — web (80/443), mail (25/587/993), SSH, databases or remote desktop — and see which are open, closed or filtered by a firewall.
Open the tool

Frequently asked questions

What is port 53?
Domain Name System lookups. Queries normally use UDP; large responses and zone transfers use TCP.
Is it safe to open port 53?
Open only if you need it. Expose it only when required, with encryption and strong authentication, ideally limited to known IP addresses.
How do I check if port 53 is open?
Enter your domain or public IP in the Port Checker with port 53. It tries a TCP connection from the internet and reports open, closed or filtered.