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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 networks (about a dozen computers). Some applications still use NetBIOS, and do not scale well in today's networks of hundreds of computers when NetBIOS is run over NBF. When properly configured, NBT allows those applications to be run on large TCP/IP networks (including the whole Internet, although that is likely to be subject to security problems) without change. NBT is defined by the RFC 1001 and RFC 1002 standard documents. == Services == NetBIOS provides four distinct services: * Name service for name registration and resolution (port: 137/udp) * Name service for name registration and resolution (port: 137/tcp) * Datagram distribution service for connectionless communication (port: 138/udp) * Session service for connection-oriented communication (port: 139/tcp) NBT implements all of those services. ===Name service=== In NetBIOS, each participant must register on the network using a unique name of at most 15 characters. In legacy networks, when a new application wanted to register a name, it had to broadcast a message saying "Is anyone currently using that name?" and wait for an answer. If no answer came back, it was safe to assume that the name was not in use. However, the wait timeout was a few seconds, making the name registration a very lengthy process, as the only way of knowing that a name was not registered was to not receive any answer. NBT can implement a central repository, or ''Name Service'', that records all name registrations. An application wanting to register a name would therefore contact the name server (which has a known network address) and ask whether the name is already registered, using a "Name Query" packet. This is much faster, as the name server returns a negative response immediately if the name is not already in the database, meaning it is available. The Name Service, according to RFCs 1001 and 1002, is called'' NetBIOS Naming Service'' or NBNS. Microsoft WINS is an implementation of NBNS. It is worth saying that due to constant development of the way in which the Name Service handles conflict or merges, "group names" varies from vendor to vendor and can even be different by version e.g. with the introduction of a service pack. The packet formats of the Name Service are identical to DNS. The key differences are the addition of NetBIOS "Node Status" query, dynamic registration and conflict marking packets. They are encapsulated in UDP. Later implementation includes an optional ''Scope'' part of the name, making NetBIOS name hierarchical like DNS, but this is seldom used. In addition, to start a session or to send a datagram to a particular host rather than to broadcast the datagram, NBT will have to determine the IP address of the host with a given NetBIOS name; this is done by broadcasting a "Name Query" packet, and/or sending it to the NetBIOS name server. The response will have the IP address of the host with that name. It is interesting to note that NBNS is one of the first proper dynamic peer-to-peer distributed name registration services. The NBNS protocol was brought into disrepute by Microsoft: it earned a bad name for being 'chatty', swamping networks with dynamic registration traffic on multiple protocols (IPX/SPX, NBF and TCP/IP) as people badly misconfigured their machines and their networks. The principles implemented in NBNS have been reimplemented many times, including in such systems as ZeroConf and MobileIP. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「NetBIOS over TCP/IP」の詳細全文を読む スポンサード リンク
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