Port 53 — DNS

Security guidance

Open recursive resolvers get abused for amplification attacks. If you run DNS, serve only your own zones or restrict recursion.

Test port 53 yourself

From your own machine, against any host (swap in your domain):

macOS / Linux — netcat

nc -vz example.com 53

Any OS — nmap

nmap -p 53 example.com

Windows — PowerShell

Test-NetConnection example.com -Port 53

open = a service answered on port 53; closed = the host replied but nothing is listening; filtered = a firewall silently dropped the probe. These test from your network — our port checker tests from the outside, the view that matters for security.

Other common ports