What port does SMB use?
SMB uses port 445 over TCP.
| Port | Protocol | Name | What it is for |
|---|---|---|---|
| 445 | TCP | SMB | Windows file and printer sharing. |
Exposing it
Should never be reachable from the internet. This is the port WannaCry and NotPetya spread over.
Checking it is listening
sudo lsof -i :445 # macOS, Linux
netstat -ano | findstr :445 # Windows
nc -zv host 445 # 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 SMB use?
SMB uses port 445 over TCP. Windows file and printer sharing.
Is port 445 safe to expose to the internet?
Should never be reachable from the internet. This is the port WannaCry and NotPetya spread over.
How do I check whether SMB is listening?
sudo lsof -i :445 on macOS or Linux, netstat -ano | findstr :445 on Windows. From another machine, nc -zv host 445 says whether anything answers.