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NetBIOS name resolution

Updated: January 21, 2005

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

NetBIOS name resolution

NetBIOS name resolution means successfully mapping a NetBIOS name to an IP address. A NetBIOS name is a 16-byte address that is used to identify a NetBIOS resource on the network. A NetBIOS name is either a unique (exclusive) or group (nonexclusive) name. When a NetBIOS process is communicating with a specific process on a specific computer, a unique name is used. When a NetBIOS process is communicating with multiple processes on multiple computers, a group name is used.

An example of a process that uses a NetBIOS name is the File and Printer Sharing for Microsoft Networks service on a computer running Windows XP Professional. When your computer starts up, this service registers a unique NetBIOS name based on the name of your computer. The exact name used by the service is the 15-character computer name plus a 16th character of 0x20. If the computer name is not 15 characters long, it is padded with spaces up to 15 characters.

When you attempt to make a file-sharing connection to a computer by using its computer name, the File and Printer Sharing for Microsoft Networks service on the file server you specify corresponds to a specific NetBIOS name. For example, when you attempt to connect to a computer called CORPSERVER, the NetBIOS name corresponding to the File and Printer Sharing for Microsoft Networks service on that computer is:

CORPSERVER     [20]

Note the use of spaces to pad the computer name. Before you can establish a file and print sharing connection, a TCP connection must be created. In order for a TCP connection to be established, the NetBIOS name "CORPSERVER     [20]" must be resolved to an IP address.

The exact mechanism by which NetBIOS names are resolved to IP addresses depends on the NetBIOS node type that is configured for the node. RFC 1001, "protocol Standard for a NetBIOS Service on a TCP/UDP Transport: Concepts and Methods," defines the NetBIOS node types, as listed in the following table.

 

Node type Description

B-node(broadcast)

B-node uses broadcast NetBIOS name queries for name registration and resolution. B-node has two major problems: (1) Broadcasts disturb every node on the network, and (2) Routers typically do not forward broadcasts, so only NetBIOS names on the local network can be resolved.

P-node (peer-peer)

P-node uses a NetBIOS name server (NBNS), such as a WINS server, to resolve NetBIOS names. P-node does not use broadcasts; instead, it queries the name server directly.

M-node (mixed)

M-node is a combination of B-node and P-node. By default, an M-node functions as a B-node. If an M-node is unable to resolve a name by broadcast, it queries a NBNS using P-node.

H-node(hybrid)

H-node is a combination of P-node and B-node. By default, an H-node functions as a P-node. If an H-node is unable to resolve a name through the NBNS, it uses a broadcast to resolve the name.

Computers running Windows Server 2003 operating systems are B-node by default and become H-node when they are configured with a WINS server. Those computers can also use a local database file called Lmhosts to resolve remote NetBIOS names. The Lmhosts file is stored in the systemroot\System32\Drivers\Etc folder. For more information, see TCP/IP database files.

It is highly recommended that you configure Windows-based computers with the IP address of your WINS server in order for remote NetBIOS names to be resolved. You must configure Active Directory-based computers, such as Windows XP Professionaland Windows Server 2003 operating systems, with the IP address of a WINS server if they are to communicate with computers running Windows NT, Windows 95, Windows 98, Windows 2000, or Windows Millennium Edition that are not Active Directory-based.

For more information about WINS, see WINS defined.

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