NetBIOS Frames protocol

From Wikipedia, the free encyclopedia

NetBIOS Frames or NBF protocol is a non-routable network- and transport-level data protocol most commonly used as one of the layers of Microsoft Windows networking. NBF protocol or NetBIOS over IEEE 802.2 LLC is used by a number of network operating systems released in the 1990s, such as LAN Manager, LAN Server, Windows for Workgroups, Windows 95 and Windows NT. Other protocols, such as NBT (NetBIOS over TCP/IP), and NetBIOS-over-IPX/SPX also implement the NetBIOS/NetBEUI services over other protocol suites.

NBF protocol is commonly confused with NetBEUI (NetBIOS Extended User Interface; an extension to the NetBIOS API that was originally developed in conjunction with NBF protocol; the two of them developed to allow NetBIOS programs to run over IBM's new token ring network)^[1]. Microsoft promulgated this confusion by labelling its NBF protocol implementation NetBEUI. NBF is a protocol and NetBEUI an API extension.

NBF protocol uses 802.2 type 1 mode to provide the NetBIOS/NetBEUI name service and datagram service, and 802.2 type 2 mode to provide the NetBIOS/NetBEUI session service (virtual circuit). NBF protocol makes wide use of broadcast messages, which accounts for its reputation as a chatty interface.

Sytek developed NetBIOS for IBM for the PC-Network program and was used by Microsoft for MS-NET in 1985. In 1987, Microsoft and Novell utilized it for their network operating systems LAN Manager and NetWare.

Because NBF protocol is unroutable it can only be used to communicate with devices in the same broadcast domain, but being bridgeable it can also be used to communicate with network segments connected each other via bridges. This means that it is only well-suited for small to medium-sized networks; the NetBIOS/NetBEUI services must be implemented atop other protocols, such as IPX and TCP/IP (see above) in order to be of use in a wide area network.^[2]

1 Services
2 Availability
3 External links
4 References

[edit] Services

NetBIOS/NetBEUI provides three distinct services:

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

NBF protocol implements all of these services.

[edit] Name service

In order to start sessions or distribute datagrams, an application must register its NetBIOS/NetBEUI name using the name service. To do so, an "Add Name Query" or "Add Group Name Query" packet is broadcast on the network. If the NetBIOS/NetBEUI name is already in use, the name service, running on the host that owns the name, broadcasts a "Node Conflict" message on the network.

In addition, to start a session or to send a datagram to a particular host rather than to broadcast the datagram, NBF protocol has to determine the MAC address of the host with a given NetBIOS/NetBEUI name; this is done by sending a "Name Query" packet, the response to which will have the MAC address of the host sending the response, i.e. the host with that name.

[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.

Sessions are established by exchanging packets. The computer establishing the session sends a "Name Query" request, specifying that a session should be initialized. The computer with which the session is to be established will respond with a "Name Recognized" response indicating either that no session can be established (either because that computer is not listening for sessions being established to that name or because no resources are available to establish a session to that name) or that a session can be established (in which case the response will include a local session number to be used in subsequent packets). The computer that is starting the session will then send a "Session Initialize" request which will prompt a "Session Confirm" response.

Data is transmitted during an established session by data packets. IEEE 802.2 handles flow control and retransmission of data packets. Because NetBIOS/NetBEUI allows packets to be sent that are larger than the largest packet that could be transmitted on a particular MAC layer, a NetBIOS/NetBEUI packet might have to be transmitted as a sequence of "Data First Middle" packets and a "Data Only Last" packet; packets that do not need to be segmented in that fashion will be sent as a single "Data Only Last" packet. An acknowledgment will be sent for all "Data Only Last" packets that are successfully received; this will also acknowledge all preceding "Data First Middle" packets.

Sessions are closed by sending a "Session End" request.

[edit] Datagram distribution service

Datagram mode is "connectionless". A datagram is sent with a "Datagram" packet if it is being sent to a particular NetBIOS/NetBEUI name, or a "Datagram Broadcast" packet if it is being sent to all NetBIOS/NetBEUI names on the network.

[edit] Availability

NBF protocol - apart from DOS and Unix implementations - is officially supported by Microsoft on almost every version of Windows until Windows 2000^[3], but its use has decreased quickly since the development of NBT.

Microsoft officially dropped its support starting from Windows XP^[4], although it still provided the user with an unsupported way to manually install it from the original CD-ROM^[5] to both encourage and ease the necessary transition to the NBT.

Because of this, officially nothing is known about whether or not NBF protocol can be unsupportedly but effectively installed on Windows Vista, and even unofficial reports seem to be unavailable on the Internet. Besides this, an additional reason of concern may be that, since the TCP/IP network stack changed significantly in Windows Vista^[6], the client ([Client for Microsoft Networks]) and server ([File and Printer Sharing for Microsoft Networks]) components - which the network protocols are bound to - could have changed too due to the rewriting process, and could have lost their previous ability to bind to the NBF protocol written for Windows XP. Despite this, it seems that installing NBF protocol on Windows Vista using NBF protocol's files taken from Windows XP original CD-ROM works effectively, with no apparent problems, and supporting all the authentication schemes (LM, NTLM, NTLMv2).