Which service is associated with TCP port 139?

Which service is associated with TCP port 139?

• A. NetBIOS (NetBIOS session service)
• B. FTP (21)
• C. SSH (22)
• D. HTTP (80)

Answer: (A)

Understanding port-to-service mappings is what this is testing. TCP port 139 is NetBIOS session service, which handles the connection-oriented SMB communications used for file and printer sharing in Windows networks. NetBIOS provides several services, with 137 (name service) and 138 (datagram) in UDP, and 139 specifically serving the session service over TCP. While SMB can also run directly over TCP port 445 in modern setups, 139 is the port historically associated with the NetBIOS session service. The other options map to different standard ports: FTP uses 21, SSH uses 22, and HTTP uses 80, so they do not correspond to 139.

Understanding port-to-service mappings is what this is testing. TCP port 139 is NetBIOS session service, which handles the connection-oriented SMB communications used for file and printer sharing in Windows networks. NetBIOS provides several services, with 137 (name service) and 138 (datagram) in UDP, and 139 specifically serving the session service over TCP. While SMB can also run directly over TCP port 445 in modern setups, 139 is the port historically associated with the NetBIOS session service. The other options map to different standard ports: FTP uses 21, SSH uses 22, and HTTP uses 80, so they do not correspond to 139.