Port 445 (SMB)
Port 445 is SMB directly over TCP (IANA name microsoft-ds): Windows file and printer sharing, network drives, Active Directory and Samba on Linux and macOS.
- Service
- SMB
- Protocol
- TCP
- IANA registry
- Officially assigned: microsoft-ds (Microsoft-DS), 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 445?
Do not expose 445 to the internet. SMB flaws have been used by worms: CVE-2017-0144 in SMBv1, fixed by Microsoft bulletin MS17-010, is the one behind the EternalBlue exploit. Block 445 at the edge, disable SMBv1, keep Windows updated and reach file shares over a VPN.
Sources
“Port 445 is already in use”: how to fix it
The error means another program is already listening on port 445. 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 :445taskkill /PID <PID> /FmacOS
lsof -nP -iTCP:445 -sTCP:LISTENkill <PID>Linux
sudo ss -ltnp | grep :445sudo lsof -i :445sudo kill <PID>Replace <PID> with the number from the last column (Windows) or the PID column (macOS, Linux).
Port 445 vs 139
Both carry Windows file sharing (SMB). 139 runs it over the old NetBIOS session layer; 445 runs SMB directly over TCP and is what modern Windows uses. Neither should be open to the internet.
Port 139 (NetBIOS)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 445 used for?
Port 445 is SMB directly over TCP (IANA name microsoft-ds): Windows file and printer sharing, network drives, Active Directory and Samba on Linux and macOS.
Is port 445 TCP or UDP?
Port 445 uses TCP. IANA reserves the number for both TCP and UDP, but in practice only TCP is used.
Is it safe to open port 445?
Do not expose 445 to the internet. SMB flaws have been used by worms: CVE-2017-0144 in SMBv1, fixed by Microsoft bulletin MS17-010, is the one behind the EternalBlue exploit. Block 445 at the edge, disable SMBv1, keep Windows updated and reach file shares over a VPN.
How do I free port 445 if it is already in use?
Find the process: on Windows run netstat -ano | findstr :445 and stop it with taskkill /PID <pid> /F; on macOS or Linux run lsof -i :445 and stop it with kill <pid>.