Understanding WINS and NetBIOS Over TCPIP

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, NBT is also installed. NBT is a session-layer service that enables NetBIOS applications to run over the TCP/IP protocol stack.

NetBIOS applications rely on WINS or the local LMHOSTS file to resolve computer names to IP addresses. On pre “Windows 2000 networks, WINS is the primary name resolution service available. On Windows Server 2003 networks, Domain Name System (DNS) is the primary name resolution service and WINS has a different role. This new role is to allow pre “Windows 2000 systems to browse lists of resources on the network and to allow Windows 2000, Windows XP, and Windows Server 2003 systems to locate NetBIOS resources.

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 another system on the network to use the computer name or IP address, or both. The names are also released when you shut down a WINS client.

Note

Configuring a WINS client is described in the section entitled "Configuring WINS Resolution" in Chapter 16 , "Managing TCP/IP Networking." Configuring a WINS server is described in the section of this chapter entitled "Configuring WINS Servers."

Name Resolution Methods

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

• B-node (broadcast)

  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. On a large network with hundreds or thousands of computers, these broadcast messages can use up valuable network bandwidth.

• P-node (peer-to-peer)

  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. In this mode, 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.

• M-node (mixed)

  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)

  Also combines b-node and p-node. With it, a WINS client first tries to use p-node for peer-to-peer name resolution. If the attempt fails, the client then tries to use broadcast messages with b-node. Because peer-to-peer 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, Windows clients use the p-node method for name resolution. If no WINS servers are available on the network, Windows clients use the b-node method for name resolution. Windows 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, "Optimizing DNS."

Tip

When you use Dynamic Host Configuration Protocol (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 entitled "Setting Scope Options" in Chapter 18 , "Running DHCP Clients and Servers." The best method to use is h-node. You'll get the best performance and have reduced traffic on the network.