NetBIOS
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NetBIOS is an acronym for Network Basic Input/Output System. It generally refers to a programming API for local network communication.
History
NetBIOS is not a networking protocol but an application programming interface, co-developed by IBM and Sytec for the so-dubbed PC-Network in the early 1980s. Although only published through a technical reference book from IBM, the protocol's API became a de-facto standard.
As PC-Network hardware is no longer used, having been replaced by TokenRing and Ethernet networks, the NetBIOS protocol might not be needed anymore. However, because a lot of software was written for NetBIOS's API, it has since been adapted to work over various other protocols such as IPX/SPX and TCP/IP.
NetBIOS over TokenRing or Ethernet is now referred to as NetBEUI. It was still heavily used until the release of Microsoft Windows 98. NetBIOS over TCP/IP is referred to as NBT and has been standardized by RFCs 1001 and 1002. NBT attempts to provide a NetBIOS-based PC-Network LAN emulation over a routed IP-based internetwork. It was introduced with Microsoft Windows 2000 and is now the preferred NetBIOS transport.
NetBIOS by itself is not routable.
Overview
NetBIOS, whatever the adaptation, provides three distinct services:
- Name service: name registration and resolution (name browsing service is part of SMB, an upper layer)
- Session service: reliable connection-oriented communication
- Datagram distribution service: unreliable connectionless communication
When NetBIOS was an OSI data link layer protocol, its functions were accessed via the 5Ch interrupt. Messages passed to these functions were formatted according to the NBC (Network Block Control) format.
NetBIOS and NetBEUI were intended for use on local networks only. Therefore, they have no support for routing and can only handle a maximum of 72 nodes or named devices. Usage of broadcast is intensive, especially for operations related to the name service.
NBT (NetBIOS over TCP/IP) uses one or more NBNS (NetBIOS Name Server(s)) to span name service over multiple subnets (while broadcast is limited to only one subnet). An NBNS is a sort of dynamic DNS. Microsoft's implementation of NBNS is called WINS. Moreover, in order to extend virtual NetBIOS networks across multiple IP subnetworks, the standard also introduced the use of one or more NBDD (NetBIOS Datagram Distribution) server(s). Unfortunately, Microsoft's implementation of NBDD never worked.
External links
- Implementing CIFS (http://ubiqx.org/cifs) (from the Samba team, published under the Open Publication License)
- NetBIOS specification (http://members.tripod.com/~Gavin_Winston/NETBIOS.HTM)
- NetBios, NetBEUI, NBF, SMB, CIFS Networking (http://timothydevans.me.uk/n2c.html)de:NETBIOS
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