Network Basic Input/Output System (NetBIOS) is a piece of software created by Sytek for IBM in 1983 which was designed to support IBM's Server Message Block (SMB) service. SMB was used by early IBM PC networks to manage server-to-client communication between IBM servers or mainframes and NetBIOS clients. NetBIOS provided the means to transport SMB information to the IBM mainframe or server. NetBIOS was adopted by Microsoft and Novell. Microsoft has since moved on to create its own Active Directory system to replace WINS and NetBIOS.

NetBIOS Names

NetBIOS uses unique 16-character names for users, services and computers. NetBIOS names must be unique and the names have no organization to them--thus all names are included in one flat namespace and cannot be organized into a hierarchical structure as modern networks are today. NetBIOS is therefore unsuited for networks that are very large or use a hierarchichal structure.

NetBIOS does not work in routed networks or internets (networks composed of 2 or more IP subnets connected by a router).

NetBIOS Services

NetBIOS uses UDP and TCP ports 137 (name service), 138 (datagram service) and 139 (session service).

Name Service (UDP 137)

NetBIOS Name Service (NBNS) provides name resolution service for computers running NetBIOS. NetBIOS Name Servers maintain a database of the NetBIOS names for hosts and the corresponding IP address the host is using.

Datagram Service (UDP 138)

NetBIOS Datagram Service is used to transfer data between systems running NetBIOS. Nearly all Datagram Service communication uses UDP

Session Service (TCP/UDP 139)

NetBIOS session service is used to setup and tear down sessions between NetBIOS capable computers.


This file is a placeholder for a future tutorial.

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