Managing WINS and NetBIOS Over TCP/IP

By William R. Stanek

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from Chapter 15, Windows NT Administrator's Pocket Consultant.

WINS (Windows Internet Name Service) is a name resolution service that resolves computer names to IP addresses. Using WINS, the computer name OMEGA, for example, could be resolved to an IP address that enables computers on a Microsoft network to find one another and transfer information.

The underlying application programming interface, or API, that enables WINS name resolution and information transfers between computers is NetBIOS (Network Basic Input/Output System). The NetBIOS API contains a set of commands that applications can use to access session-layer services. Commonly used extensions for NetBIOS are NetBEUI (NetBIOS Enhanced User Interface) and NBT (NetBIOS over TCP/IP). This chapter focuses on WINS and NBT.

Understanding WINS and NetBIOS Over TCP/IP

WINS works best in client-server environments where WINS clients send queries to WINS servers for name resolution and WINS servers resolve the query and respond. To transmit WINS queries and other information, computers use NetBIOS. NetBIOS provides an API that allows computers on a network to communicate. When you install TCP/IP networking on a Microsoft client or server, NetBIOS over TCP/IP is also installed. NetBIOS over TCP/IP is a session-layer service that enables NetBIOS applications to run over the TCP/IP protocol stack. NetBIOS applications, such as the command-line NET utilities, rely on WINS or the local LMHOSTS file to resolve computer names to IP addresses.

Using DNS

WINS isn't the only name resolution service available. You can also use DNS (Domain Name Service). DNS is a name resolution service that resolves Internet host names to IP addresses. Using DNS, you can resolve the fully qualified domain name www.centraldrive.com, for example, to an IP address. While WINS is used with NetBIOS applications, DNS is used with Winsock applications that operate over the TCP/IP protocol stack, such as FTP or Telnet. DNS can be configured to work in conjunction with WINS.

Configuring WINS Clients and Servers

To enable WINS name resolution on a network, you need to configure WINS clients and servers. When you configure WINS clients, you tell the clients the IP addresses of WINS servers on the network. Using the IP address, clients can communicate with WINS servers anywhere on the network, even if the servers are on different subnets. WINS clients can also communicate using a broadcast method in which clients broadcast messages to other computers on the local network segment requesting their IP addresses. Because messages are broadcast, the WINS server isn't used. Any non-WINS clients that support this type of message broadcasting can also use this method to resolve computer names to IP addresses.

When clients communicate with WINS servers, they establish sessions that have three key parts:

• Name registration During name registration, the client gives the server its computer name and its IP address and asks to be added to the WINS database. If the specified computer name and IP address aren't already in use on the network, the WINS server accepts the request and registers the client in the WINS database.

• Name renewal Name registration isn't permanent. Instead, the client has use of the name for a specified period, which is known as a lease. The client is also given a time period within which the lease must be renewed, which is known as the renewal interval. The client must reregister with the WINS server during the renewal interval.

• Name release If the client can't renew the lease, the name registration is released, allowing the computer name or IP address, or both, to be used by another system on the network. The names are also released when you shutdown a WINS client.

Note: Configuring a WINS client is described in the section of Chapter 12 titled "Configuring WINS Resolution." Configuring a WINS server is described in this chapter under "Installing WINS Servers."

Name Resolution Methods

Once a client establishes a session with a WINS server, the client can request name resolution services. The method used to resolve computer names to IP addresses depends on how the network is configured. Four name resolution methods are available:

• B-node (Broadcast node) B-node uses broadcast messages to resolve computer names to IP addresses. Computers that need to resolve a name broadcast a message to every host on the local network, requesting the IP address for a computer name.

  B-node has two strengths. First, you don't need to configure a WINS server to use this method. Second, some non-WINS clients support b-node and—in conjunction with at least one WINS client (acting as a proxy)—can resolve computer names using this method. Also, b-node can be used with a local LMHOSTS file, which would enable name resolution on subnets.

  B-node has two weaknesses. The method isn't routable and you can't use it to resolve names across routers. Broadcast messages can generate a lot of traffic on the network, especially as the number of computers on the network grows.

• P-node (Point-to-point node) P-node uses WINS servers to resolve computer names to IP addresses. As explained earlier, client sessions have three parts: name registration, name renewal, and name release. When a client needs to resolve a computer name to an IP address, the client sends a query message to the server and the server responds with an answer.

  The main strength of p-node is that it's point-to-point and doesn't use a lot of network bandwidth. P-node is also routable, which enables clients to query servers across routers. However, any time the server is down or otherwise unavailable, name resolution fails.

• M-node (Modified node) M-node is a modified mode that combines b-node and p-node. With it, a WINS client first tries to use b-node for name resolution. If the attempt fails, the client then tries to use p-node. Because b-node is used first, this method has the same problems with network bandwidth usage as b-node.

• H-node (Hybrid node) H-node also combines b-node and p-node. With it, a WINS client first tries to use p-node for point-to-point name resolution. If the attempt fails, the client then tries to use broadcast messages with b-node. Because point-to-point is the primary method, h-node offers the best performance on most networks. H-node is also the default method for WINS name resolution.

  If WINS servers are available on the network, Microsoft Windows NT clients use the p-node method for name resolution. If no WINS servers are available on the network, Windows NT clients use the b-node method for name resolution. Windows NT computers can also use DNS and the local files LMHOSTS and HOSTS to resolve network names. Working with DNS is covered in the next chapter.

Tip: When you use DHCP to dynamically assign IP addresses, you should set the name resolution method for DHCP clients. To do this, you need to set DHCP scope options for the 046 WINS/NBT Node Type as specified in the section of Chapter 14 titled "Setting Default WINS Servers for DHCP Clients." The best method to use is h-node. You'll get the best performance and have reduced traffic on the network.

from Windows NT Administrator's Pocket Consultant by William R. Stanek. Copyright © 1999 Microsoft Corporation.

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