Ports 137 and 139 are associated with NetBIOS/NetBT (NetBIOS over TCP/IP) services. Port 137 is used by the NetBIOS Name Service (NBNS) for name resolution, allowing machines on a local network to find each other by name. Port 139 is used for the NetBIOS Session Service (NBSession), facilitating connection-oriented communication between computers for services like file and print sharing. In modern networks, SMB (Server Message Block) often runs directly over TCP port 445, but these legacy NetBIOS ports are still relevant for backward compatibility. Port 135 is used for RPC Endpoint Mapper and is not directly part of NetBIOS services.
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