What port does DNS use?
DNS uses port 53 over TCP/UDP.
| Port | Protocol | Name | What it is for |
|---|---|---|---|
| 53 | TCP/UDP | DNS | Domain name resolution. UDP for normal queries, TCP for responses over 512 bytes and for zone transfers. |
Exposing it
An open recursive resolver will be abused for DNS amplification attacks. Restrict recursion to your own networks.
Checking it is listening
sudo lsof -i :53 # macOS, Linux
netstat -ano | findstr :53 # Windows
nc -zv host 53 # from elsewhereAn "address already in use" error on a port nothing appears to be holding usually means the socket is in TIME_WAIT rather than that a process has it — the ports reference covers that and the ephemeral range.
Frequently asked questions
What port does DNS use?
DNS uses port 53 over TCP/UDP. Domain name resolution. UDP for normal queries, TCP for responses over 512 bytes and for zone transfers.
Is port 53 safe to expose to the internet?
An open recursive resolver will be abused for DNS amplification attacks. Restrict recursion to your own networks.
How do I check whether DNS is listening?
sudo lsof -i :53 on macOS or Linux, netstat -ano | findstr :53 on Windows. From another machine, nc -zv host 53 says whether anything answers.