NetBIOS Datagram Service uses which port number?

NetBIOS Datagram Service uses which port number?

• A. 138
• B. 139
• C. 137
• D. 119

Answer: (A)

NetBIOS over TCP/IP provides three main services, each with its own port. The Datagram Service is the UDP-based, connectionless transport used to send NetBIOS datagrams. Because it’s datagram-oriented, it uses UDP, and the standard UDP port for this service is 138. By contrast, NetBIOS Name Service uses UDP port 137 for name registration and resolution, and the NetBIOS Session Service uses TCP port 139 to establish a session between NetBIOS names. Port 119 is not part of NetBIOS—it’s used for NNTP. So the Datagram Service’s port is 138.

NetBIOS over TCP/IP provides three main services, each with its own port. The Datagram Service is the UDP-based, connectionless transport used to send NetBIOS datagrams. Because it’s datagram-oriented, it uses UDP, and the standard UDP port for this service is 138. By contrast, NetBIOS Name Service uses UDP port 137 for name registration and resolution, and the NetBIOS Session Service uses TCP port 139 to establish a session between NetBIOS names. Port 119 is not part of NetBIOS—it’s used for NNTP. So the Datagram Service’s port is 138.