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Networking Fundamentals · Intermediate

NetBIOS

A legacy API and set of services for name resolution and sessions on Windows networks, using UDP 137, UDP 138 and TCP 139.

Definition

NetBIOS over TCP/IP provides name service (137), datagram service (138) and session service (139). It has been largely replaced by DNS and direct SMB on 445, and its name broadcasts can be abused for credential capture.

Example

nbtstat -n lists a Windows host's NetBIOS names.

Exam tip

NetBIOS = 137-139; SMB direct = 445.

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