NetBT

NetBT, short for NetBIOS over TCP/IP, is a networking protocol that enables NetBIOS applications to operate across IP networks by providing NetBIOS services over TCP/IP. It comprises three primary service types: NetBIOS Name Service (NBNS) for name registration and resolution, NetBIOS Datagram Service (NBDS) for connectionless datagrams, and NetBIOS Session Service (NBSS) for connection-oriented sessions. These services typically use UDP port 137 for NBNS, UDP port 138 for NBDS, and TCP port 139 for NBSS.

NetBIOS is a legacy API that predates IP, originally used by Windows desktop and server software for file and printer sharing. NetBT allows these NetBIOS applications to run on IP networks and to use NBNS for name-to-address mapping and NBSS for sessions, with SMB commonly transported on top of NetBIOS. In modern Windows networks, DNS is typically used for host name resolution, and SMB traffic can run directly over TCP port 445, with NetBIOS over TCP/IP retained for compatibility in mixed environments.

Configuration and status: NetBIOS over TCP/IP can be enabled or disabled on individual network adapters. Many organizations disable it to reduce broadcast traffic and limit potential security risks. When NetBT is disabled, NetBIOS name resolution relies on other mechanisms such as DNS, and legacy NetBIOS-based applications may require alternative configurations or compatibility modes.

Implementations: NetBT is supported by Windows operating systems and by Samba in non-Windows environments to maintain compatibility with older SMB/CIFS networks. It remains a historical cornerstone of Windows networking but is largely considered optional in modern networks.