NetBIOS

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"NetBEUI" redirects here. (IPA: / ˈnɛtˌbuɪ/) This can also refer to Microsoft's implementation of NetBIOS Frames protocol, a related but distinct technology.

NetBIOS (IPA: / ˈnɛtˌbʌɪɒs/) is an acronym for Network Basic Input/Output System. The NetBIOS API allows applications on separate computers to communicate over a local area network. In modern networks, it normally runs over TCP/IP (NetBIOS over TCP/IP, or NBT), giving each computer in the network both a NetBIOS name and an IP address corresponding to a (possibly different) host name. Older operating systems ran NetBIOS over IPX/SPX or IEEE 802.2 (NBF). NetBIOS provides services related to the session layer of the OSI model.

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[edit] NetBIOS name vs host name

When NetBIOS is run over the TCP/IP protocol, each computer may have multiple "names" — names for the NetBIOS API and another (or others) for basic TCP/IP.

[edit] NetBIOS name

The NetBIOS name is specified when Windows networking is installed/configured. In order to connect to a computer running TCP/IP via its NetBIOS name, the name must be resolved to a network address. Today this is usually an IP address (the NetBIOS name-IP address resolution is often done by either broadcasts or a WINS Server — NetBIOS Name Server). A computer's NetBIOS name is often the same as that computer's host name (see below), although truncated to 15 characters, but it may also be completely different. NetBIOS names can include almost any combination of alphanumeric characters except for spaces and the following characters: \ / : * ? " ; | The Windows LMHOSTS file provides a NetBIOS name resolution method that can be used for small networks that do not use a WINS server.

[edit] Host name

A Windows machine's NetBIOS name is not to be confused with the computer's host name. Generally a computer running TCP/IP (whether it's a Windows machine or not) has a host name (also sometimes called a machine name or a DNS name). Generally the host name of a Windows computer is based on the NetBIOS name plus the Primary DNS Suffix, which are both set in the System Control Panel.

There may also be "connection specific suffixes" which can be viewed or changed on the DNS tab in Control Panel → Network → TCP/IP → Advanced Properties. Host names are used by applications such as telnet, ftp, web browsers, etc. In order to connect to a computer running the TCP/IP protocol using its HOST name, the host name must be resolved into an IP Address. Host name- or Fully Qualified Domain Name (FQDN)-IP address resolution is typically done by a Domain Name System (DNS) server..

[edit] Node types

The node type of a networked computer relates to the way it resolves NetBIOS names to IP addresses. There are four node types.

  • B-node: 0x01 Broadcast
  • P-node: 0x02 Peer (WINS only)
  • M-node: 0x04 Mixed (broadcast, then WINS)
  • H-node: 0x08 Hybrid (WINS, then broadcast)

The node type in use is displayed by opening a command line and typing ipconfig /all. A Windows computer registry may also be configured in such a way as to display "unknown" for the node type.

[edit] History

NetBIOS was developed by Sytek Inc. for IBM's PC-Network in 1983. The interface was designed for small networks; PC-Network only supported up to 80 devices in its baseband form. Since its original publishing in a technical reference book from IBM, the protocol's API has become a de facto standard.

In 1985, IBM went forward with the token ring network scheme and a NetBIOS emulator was produced to allow PC-Network applications to work over this new design, using the NBF protocol to provide the NetBIOS services over the IEEE 802.2 Logical Link Control layer. This emulator also expanded upon the base NetBIOS API and the new API was deemed NetBEUI or NetBIOS Extended User Interface. With Novell's release of Advanced Novell NetWare 2.0 in 1986, NetBIOS was reconfigured to be encapsulated in the IPX/SPX protocol. After the PS/2 computer hit the market in 1987 IBM was finally prompted to release the PC LAN Support Program, which included a driver for NetBIOS.

In 1987, a method of encapsulating NetBIOS in TCP and UDP packets, NetBIOS over TCP/IP (NBT), was published; it is described in RFC 1001 — "Protocol Standard for a NetBIOS Service on a TCP/UDP Transport: Concepts and methods" and RFC 1002 — "Protocol standard for a NetBIOS service on a TCP/UDP transport: Detailed specifications". This was developed in order to "allow an implementation [of NetBIOS applications] to be built on virtually any type of system where the TCP/IP protocol suite is available" and to "allow NetBIOS interoperation in the Internet".

[edit] Services

NetBIOS provides three distinct services:

  • Name service for name registration and resolution.
  • Session service for connection-oriented communication.
  • Datagram distribution service for connectionless communication.

(Note: SMB, an upper layer, is a service that runs on top of the Session Service and the Datagram service, and is not to be confused as a necessary and integral part of NetBIOS itself. It can now run atop TCP with a small adaptation layer that adds a packet length to each SMB message; this is necessary because TCP only provides a byte-stream service with no notion of packet boundaries.)

[edit] Name service

In order to start Sessions or distribute Datagrams, an application must register its NetBIOS name using the Name service. NetBIOS names are 16 bytes in length and vary based on the particular implementation. Frequently, the 16th byte is used to designate a "type" similar to the use of ports in TCP/IP. In NBT, the name service operates on UDP port 137 (TCP port 137 can also be used, but it is rarely if ever used).

The name service primitives offered by NetBIOS are:

  • Add Name — registers a NetBIOS name.
  • Add Group Name — registers a NetBIOS "group" name.
  • Delete Name — un-registers a NetBIOS name or group name.
  • Find Name — looks up a NetBIOS name on the network.

[edit] Session service

Session mode lets two computers establish a connection for a "conversation", allows larger messages to be handled, and provides error detection and recovery. In NBT, the session service runs on TCP port 139.

The session service primitives offered by NetBIOS are:

  • Call — opens a session to a remote NetBIOS name.
  • Listen — listen for attempts to open a session to a NetBIOS name.
  • Hang Up — close a session.
  • Send — sends a packet to the computer on the other end of a session.
  • Send No Ack — like Send, but doesn't require an acknowledgment.
  • Receive — wait for a packet to arrive from a Send on the other end of a session.

In the original protocol used to implement NetBIOS services on PC-Network, to establish a session, the computer establishing the session sends an Open request which is responded to by an Open acknowledgment. The computer that started the session will then send a Session Request packet which will prompt either a Session Accept or Session Reject packet. Data is transmitted during an established session by data packets which are responded to with either acknowledgment packets (ACK) or negative acknowledgment packets (NACK). Since NetBIOS is handling the error recovery, NACK packets will prompt retransmission of the data packet. Sessions are closed by the non-initiating computer by sending a close request. The computer that started the session will reply with a close response which prompts the final session closed packet.

[edit] Datagram distribution service

Datagram mode is "connectionless". Since each message is sent independently, they must be smaller; the application becomes responsible for error detection and recovery. In NBT, the datagram service runs on UDP port 138.

The datagram service primitives offered by NetBIOS are:

  • Send Datagram — send a datagram to a remote NetBIOS name.
  • Send Broadcast Datagram — send a datagram to all NetBIOS names on the network.
  • Receive Datagram — wait for a packet to arrive from a Send Datagram operation.
  • Receive Broadcast Datagram — wait for a packet to arrive from a Send Broadcast Datagram operation.

[edit] See also

[edit] External links

[edit] References

  • Haugdahl, J. Scott (1990). Inside NetBIOS. Architecture Technology Corp. ISBN 99914-57-34-8
  • Silberschatz, Abraham; Galvin, Peter Baer; Gagne, Greg (2004). Operating System Concepts. (7th Ed.). John Wiley & Sons. ISBN 0-471-69466-5
  • Meyers, Michael (2004). "Managing and Troubleshooting Networks". McGraw-Hill. ISBN 978-0-07-225665-9