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Microsoft-DS / SMB
Port 445 is primarily used for Microsoft Directory Services (Microsoft-DS), supporting file sharing, printer sharing, and access to Active Directory via the Server Message Block (SMB) protocol over TCP. It has replaced older NetBIOS ports, facilitating more efficient direct communication, and is widely deployed across Windows environments for seamless network resource access..
Port 445 is designated for direct hosting of the Server Message Block (SMB) protocol over TCP/IP, superseding older implementations that relied on NetBIOS over TCP (ports 137-139). This facilitates network file and printer sharing, as well as Active Directory operations like authentication and replication. Microsoft's implementation of SMB on port 445 enables seamless access to resources across Windows networks without the overhead of legacy protocols.
Technically, SMB is an application-layer network protocol primarily designed to provide shared access to files and printers. The shift to direct hosting over port 445 modernized communication by reducing protocol complexity, improving performance, and enabling better integration with other Windows network services. Active Directory heavily relies on SMB for various directory-related operations, making port 445 vital to Windows domain functionality.
Beyond Windows, some UNIX-like systems via Samba have implemented SMB compatibility, enhancing interoperability in mixed-OS environments. However, this broad utility also means the port is widely exposed and targeted if improperly secured. Managing access to port 445 is critical in enterprise networks to maintain both operability and security.