File sharing, printer sharing, and other SMB exchanges on Windows networks.
What is Port 445 used for?
Windows file sharing. The protocol or service commonly associated with this port is SMB / CIFS.
Role and operation
An SMB client opens a TCP session to the server on port 445, negotiates the protocol version, authenticates, and then accesses authorized shares and resources. Modern SMB uses TCP 445 directly and does not depend on NetBIOS for its primary transport.
Transport protocol
TCP
Security precautions
Should this port be opened in the firewall?
Open TCP 445 only between workstations, servers, and network segments that genuinely need SMB. Block it at Internet boundaries and restrict lateral access through segmentation and firewall policy.
How can this port be checked?
On Windows, test connectivity with Test-NetConnection SERVER -Port 445. Add SMB logs, Get-SmbConnection on the client, or a packet capture when authentication or protocol negotiation fails.
Port-to-service mappings are common conventions. An application may be configured on another port or use a different transport depending on its implementation.