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NetBIOS Datagram Service
NetBIOS Datagram Service (port 138) facilitates connectionless communication primarily for NetBIOS over TCP/IP networks. It is used extensively in Windows network environments for tasks such as name service browsing and datagram distribution, aiding functions like resource sharing and messaging within local networks..
NetBIOS Datagram Service operating over port 138 is a core component of the NetBIOS over TCP/IP suite (NBT). It supports connectionless communication, enabling broadcast and multicast datagrams for providing name resolution, host announcements, and browsing services on local subnets. This allows Windows systems to discover each other, share resources, and broadcast status updates without an established session.
Technically, the Datagram Service complements the other NetBIOS services like the Name Service (port 137) and Session Service (port 139). It relies primarily on UDP, though some implementations may respond over TCP for compatibility. Datagram packets are used to transmit small messages across the local network, such as browsing announcements, mailslots messaging, and system notifications, contributing to NetBIOS name resolution and distributed network management.
Because communication is connectionless, delivery is not guaranteed, making it suitable for scenarios where best-effort delivery suffices. This behavior reduces overhead but may increase network noise due to frequent broadcasts. Consequently, NetBIOS Datagram Service is typically confined to internal scopes like LANs, with modern networks often limiting or replacing it with DNS and newer protocols.