NetBIOS () is an acronym for Network Basic Input/Output System. It provides services related to the

session layer In the seven-layer OSI model of computer networking, the session layer is layer 5. The session layer provides the mechanism for opening, closing and managing a session between end-user application processes, i.e., a semi-permanent dialogue. ...

of the

OSI model The Open Systems Interconnection model (OSI model) is a conceptual model that 'provides a common basis for the coordination of SOstandards development for the purpose of systems interconnection'. In the OSI reference model, the communications ...

allowing applications on separate computers to communicate over a

local area network A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building. By contrast, a wide area network (WAN) not only covers a larger ...

. As strictly an

API An application programming interface (API) is a way for two or more computer programs to communicate with each other. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how ...

, NetBIOS is not a

networking protocol A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules, syntax, semantics and synchroniza ...

. Older

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...

s ran NetBIOS over

IEEE 802.2 IEEE 802.2 is the original name of the ISO/IEC 8802-2 standard which defines logical link control (LLC) as the upper portion of the data link layer of the OSI Model. The original standard developed by the Institute of Electrical and Electronics Engi ...

and

IPX/SPX IPX/SPX stands for Internetwork Packet Exchange/Sequenced Packet Exchange. IPX and SPX are networking protocols used initially on networks using the (since discontinued) Novell NetWare operating systems. They also became widely used on netwo ...

using the

NetBIOS Frames NetBIOS Frames (NBF) is a non- routable network- and transport-level data protocol most commonly used as one of the layers of Microsoft Windows networking in the 1990s. NBF or NetBIOS over IEEE 802.2 LLC is used by a number of network operating s ...

(NBF) and

NetBIOS over IPX/SPX NetBIOS () is an acronym for Network Basic Input/Output System. It provides services related to the session layer of the OSI model allowing applications on separate computers to communicate over a local area network. As strictly an API, NetB ...

(NBX) protocols, respectively. In modern networks, NetBIOS normally runs over

TCP/IP The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...

via the

NetBIOS over TCP/IP NetBIOS over TCP/IP (NBT, or sometimes NetBT) is a networking protocol that allows legacy computer applications relying on the NetBIOS API to be used on modern TCP/IP networks. NetBIOS was developed in the early 1980s, targeting very small network ...

(NBT) protocol. This results in each computer in the network having both an

IP address An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...

and a NetBIOS name corresponding to a (possibly different) host name. NetBIOS is also used for identifying system names in TCP/IP (Windows). Simply saying, it is a protocol that allows communication of files and printers through the Session Layer of the OSI Model in a LAN.

History and terminology

NetBIOS is a non-routable OSI Session Layer 5 Protocol and a service that allows applications on computers to communicate with one another over a

(LAN). NetBIOS was developed in 1983 by Sytek Inc. as an

for software communication over

IBM PC Network The IBM PC Network was IBM PC's first LAN system. It consisted of network cards, cables, and a small device driver known as NetBIOS (Network Basic Input/Output System). It used a data rate of 2 Mbit/s and carrier-sense multiple access with colli ...

LAN technology. On

, as an API alone, NetBIOS relied on proprietary Sytek networking protocols for communication over the wire. Despite supporting a maximum of 80 PCs in a LAN, NetBIOS became an industry standard. In 1985, IBM went forward with the

Token Ring Token Ring network IBM hermaphroditic connector with locking clip. Screen contacts are prominently visible, gold-plated signal contacts less so. Token Ring is a computer networking technology used to build local area networks. It was introduc ...

network scheme and a NetBIOS

emulator In computing, an emulator is hardware or software that enables one computer system (called the ''host'') to behave like another computer system (called the ''guest''). An emulator typically enables the host system to run software or use pe ...

was produced to allow NetBIOS-aware applications from the PC-Network era to work over this new design. This emulator, named NetBIOS Extended User Interface (NetBEUI), expanded the base NetBIOS API with, among other things, the ability to deal with the greater node capacity of Token Ring. A new networking protocol, NBF, was simultaneously produced to allow NetBEUI (NetBIOS) to provide its services over Token Ring – specifically, at the

Logical Link Control In the IEEE 802 reference model of computer networking, the logical link control (LLC) data communication protocol layer is the upper sublayer of the data link layer (layer 2) of the seven-layer OSI model. The LLC sublayer acts as an interface ...

layer. In 1985,

Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washing ...

created a NetBIOS implementation for its

MS-Net MS-Net, sometimes stylized as MS-NET, was an early network operating system sold by Microsoft during the earliest days of local area networking (LANs). Overview MS-Net was not a complete networking system of its own; Microsoft licensed it to vend ...

networking technology. As in the case of IBM's Token Ring, the services of Microsoft's NetBIOS implementation were provided over the IEEE 802.2 Logical Link Control layer by the NBF protocol. Until Microsoft adopted

Domain Name System The Domain Name System (DNS) is a hierarchical and distributed naming system for computers, services, and other resources in the Internet or other Internet Protocol (IP) networks. It associates various information with domain names assigned to ...

(DNS) resolution of

hostname In computer networking, a hostname (archaically nodename) is a label that is assigned to a device connected to a computer network and that is used to identify the device in various forms of electronic communication, such as the World Wide Web. Hos ...

s, Microsoft operating systems used NetBIOS to resolve names in Windows client-server networks. In 1986,

Novell Novell, Inc. was an American software and services company headquartered in Provo, Utah, that existed from 1980 until 2014. Its most significant product was the multi-platform network operating system known as Novell NetWare. Under the lead ...

released Advanced

Novell NetWare NetWare is a discontinued computer network operating system developed by Novell, Inc. It initially used cooperative multitasking to run various services on a personal computer, using the IPX network protocol. The original NetWare product in ...

2.0 featuring the company's own NetBIOS emulator. Its services were encapsulated within NetWare's

protocol using the

(NBX) protocol. In 1987, a method of encapsulating NetBIOS in TCP and UDP packets,

(NBT), was published. It was 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"). The NBT protocol was developed in order to "allow an implementation f NetBIOS applicationsto be built on virtually any type of system where the TCP/IP protocol suite is available," and to "allow NetBIOS interoperation in the Internet." After the PS/2 computer hit the market in 1987, IBM released the PC LAN Support Program, which included a driver for NetBIOS. There is some confusion between the names NetBIOS and NetBEUI. NetBEUI originated strictly as the

moniker A nickname is a substitute for the proper name of a familiar person, place or thing. Commonly used to express affection, a form of endearment, and sometimes amusement, it can also be used to express defamation of character. As a concept, it is ...

for IBM's enhanced 1985 NetBIOS emulator for Token Ring. The name NetBEUI should have died there, considering that at the time, the NetBIOS implementations by other companies were known simply as NetBIOS regardless of whether they incorporated the API extensions found in that emulator. For MS-Net, however, Microsoft elected to name its implementation of the NBF protocol "NetBEUI" – naming its implementation of the transport protocol after IBM's second version of the API. Consequently Microsoft file and printer sharing over

Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...

continues to be called NetBEUI, with the name NetBIOS commonly used only in for file and printer sharing over

. More accurately, the former is

(NBF), and the latter is

(NBT). Since its original publishing in a technical reference book from IBM, the NetBIOS API specification has become a ''de facto'' standard.

Services

NetBIOS provides three distinct services: *Name service (NetBIOS-NS) for name registration and

resolution Resolution(s) may refer to: Common meanings * Resolution (debate), the statement which is debated in policy debate * Resolution (law), a written motion adopted by a deliberative body * New Year's resolution, a commitment that an individual mak ...

. *

Datagram A datagram is a basic transfer unit associated with a packet-switched network. Datagrams are typically structured in header and payload sections. Datagrams provide a connectionless communication service across a packet-switched network. The del ...

distribution service (NetBIOS-DGM) for connectionless communication. * Session service (NetBIOS-SSN) for

connection-oriented communication Connection-oriented communication is a network communication mode in telecommunications and computer networking, where a communication session or a semi-permanent connection is established before any useful data can be transferred. The establish ...

. (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 length field to each SMB message; this is necessary because TCP only provides a byte-stream service with no notion of message boundaries.)

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 octets in length and vary based on the particular implementation. Frequently, the 16th octet, called the NetBIOS Suffix, designates the type of resource, and can be used to tell other applications what type of services the system offers. In NBT, the name service operates on UDP port 137 (TCP port 137 can also be used, but rarely is). 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. NetBIOS name resolution is not supported by Microsoft for Internet Protocol Version 6 (IPv6).

Datagram distribution service

Datagram mode is

connectionless Connectionless communication, often referred to as CL-mode communication,Information Processing Systems - Open Systems Interconnection, "Transport Service Definition - Addendum 1: Connectionless-mode Transmission", International Organization for ...

; the application is 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.

Session service

Session mode lets two computers establish a connection, allows messages to span multiple packets, 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 initiating computer sends an Open request which is answered 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. During an established session, each transmitted packet is answered by either a positive-acknowledgment (ACK) or negative-acknowledgment (NAK) response. A NAK will prompt retransmission of the data. 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.

NetBIOS name vs Internet host name

When NetBIOS is run in conjunction with

Internet protocol The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. IP h ...

s (e.g., NBT), each computer may have multiple names: one or more NetBIOS name service names and one or more Internet host names.

NetBIOS name

The NetBIOS name is 16 ASCII characters, however Microsoft limits the host name to 15 characters and reserves the 16th character as a NetBIOS Suffix. This suffix describes the service or name record type such as host record, master browser record, or domain controller record or other services. The host name (or short host name) is specified when Windows networking is installed/configured, the suffixes registered are determined by the individual services supplied by the host. In order to connect to a computer running TCP/IP via its NetBIOS name, the name must be resolved to a

network address A network address is an identifier for a node or host on a telecommunications network. Network addresses are designed to be unique identifiers across the network, although some networks allow for local, private addresses, or locally administere ...

. Today this is usually an

(the NetBIOS name to 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 are a sequence of alphanumeric characters. The following characters are explicitly not permitted: \/:*?"<>, . Since Windows 2000, NetBIOS names also had to comply with restrictions on DNS names: they cannot consist entirely of digits, and the hyphen ("-") or full-stop (".") characters may not appear as the first or last character. Since Windows 2000, Microsoft has advised against including any full-stop (".") characters in NetBIOS names, such that applications can use the presence of a full-stop to distinguish domain names from NetBIOS names. The Windows LMHOSTS file provides a NetBIOS name resolution method that can be used for small networks that do not use a WINS server.

Internet host name

A Windows machine's NetBIOS name is not to be confused with the computer's Internet host name (assuming that the computer is also an Internet host in addition to being a NetBIOS node, which need not necessarily be the case). Generally a computer running Internet protocols (whether it is a Windows machine or not) usually has a host name (also sometimes called a machine name). Originally these names were stored in and provided by a

hosts file The computer file hosts is an operating system file that maps hostnames to IP addresses. It is a plain text file. Originally a file named HOSTS.TXT was manually maintained and made available via file sharing by Stanford Research Institute for the ...

but today most such names are part of the hierarchical

(DNS). 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 Properties dialog box. 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 Application may refer to: Mathematics and computing * Application software, computer software designed to help the user to perform specific tasks ** Application layer, an abstraction layer that specifies protocols and interface methods used in a c ...

such as

telnet Telnet is an application protocol used on the Internet or local area network to provide a bidirectional interactive text-oriented communication facility using a virtual terminal connection. User data is interspersed in-band with Telnet control i ...

ftp The File Transfer Protocol (FTP) is a standard communication protocol used for the transfer of computer files from a server to a client on a computer network. FTP is built on a client–server model architecture using separate control and data ...

web browser A web browser is application software for accessing websites. When a user requests a web page from a particular website, the browser retrieves its files from a web server and then displays the page on the user's screen. Browsers are used on ...

s, etc. To connect to a computer running the TCP/IP protocol using its name, the host name must be resolved into an

, typically by a DNS server. (It is also possible to operate many TCP/IP-based applications, including the three listed above, using only IP addresses, but this is not the norm.)

Node types

Under Windows, the node type of a networked

computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as C ...

relates to the way it resolves NetBIOS names to

es. This assumes that there are any IP addresses for the NetBIOS nodes, which is assured only when NetBIOS operates over NBT; thus, node types are not a property of NetBIOS per se but of interaction between NetBIOS and TCP/IP in the Windows OS environment. 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 A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...

and typing ''ipconfig /all''. A

Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...

computer registry may also be configured in such a way as to display "unknown" for the node type.

NetBIOS Suffixes

The NetBIOS Suffix, alternately called the NetBIOS End Character (endchar), is the 16th character of a NetBIOS name and indicates service type for the registered name. The number of record types is limited to 255; some commonly used values are: For unique names: *00: Workstation Service (workstation name) *03:

Windows Messenger service Messenger service is a network-based system notification Windows service by Microsoft that was included in some earlier versions of Microsoft Windows. This retired technology, although it has a similar name, is not related in any way to the l ...

*06:

Remote Access Service A remote access service (RAS) is any combination of hardware and software to enable the remote access tools or information that typically reside on a network of IT devices. A remote access service connects a client to a host computer, known as a ...

*20: File Service (also called Host Record) *21:

client *1B:

Domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a partial function **Domain of holomorphy of a function * Do ...

Master Browser – Primary Domain Controller for a domain *1D: Master Browser For group names: *00: Workstation Service (workgroup/domain name) *1C:

Domain Controllers On Microsoft Servers, a domain controller (DC) is a server computer that responds to security authentication requests (logging in, etc.) within a Windows domain. A ''domain'' is a concept introduced in Windows NT whereby a user may be granted access ...

for a domain (group record with up to 25 IP addresses) *1E: Browser Service Elections

References

External links

* /publib.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/BK8P7001/CCONTENTS LAN Technical Reference: 802.2 and NetBIOS APIs
Implementing CIFS
(from the

Samba Samba (), also known as samba urbano carioca (''urban Carioca samba'') or simply samba carioca (''Carioca samba''), is a Brazilian music genre that originated in the Afro-Brazilian communities of Rio de Janeiro in the early 20th century. Havin ...

team, published under the

Open Publication License The Open Publication License (OPL) was published by the Open Content Project in 1999 as a public copyright license for documents. It superseded the Open Content License, which was published by the Open Content Project in 1998. Starting around 2 ...

)
NetBIOS, NetBEUI, NBF, SMB, CIFS Networking

LMHOSTS File

NETBIOS End Characters / Suffixes
– Microsoft Knowledge Base article describing list of NetBIOS Suffixes.

– Visual Basic 2010 NetBIOS API source code. * {{DEFAULTSORT:Netbios Network protocols