Configuring NetBIOS Name Resolution

Microsoft TCP/IP uses NetBIOS over TCP/IP (NetBT) as specified in RFCs 1001 and 1002 to support the NetBIOS client and server programs in the LAN and WAN environments. Before we discuss the specifics of NetBIOS name resolution, let's briefly review how computers communicate on the network. This should help in understanding how the various NetBIOS modes work and why some are preferable to others.

Computers can communicate on a network in two ways:

• Through broadcast messages, which every computer receives.

• Through directed messages, which are sent to a specific computer.

Whenever possible, it was preferable to communicate through directed messages. This cut down on the amount of network traffic and ensured that only the affected hosts received the message. This also ensured that the messages propagated across routers. Because of this, Microsoft needed to ensure that WINS communicated primarily with directed messages. The company accomplished this by allowing several types of NetBIOS naming methods. These naming methods are commonly called node types. A node is simply a device on a network. Every computer running a Microsoft OS is configured to use one of four node types. The node type determines whether the computer will register and resolve names through broadcast messages, directed messages, or some combination of broadcast and directed messages.

Exam Alert: Microsoft Does Test on Backward Compatibility

Don't be fooled. Just because WINS is a legacy technology doesn't mean you won't be tested on it on the exam. Microsoft recognizes the importance of backward compatibility, and as a result, you can expect to see questions about WINS on this exam. If you have not worked with it in a legacy environment, take the necessary steps to make sure you understand how WINS works.

Before you can work with WINS, you need to know what the node types are and when they are used:

• b-node (broadcast node) Relies exclusively on broadcast messages and is the oldest NetBIOS name registration and resolution mode. A host needing to resolve a name request sends a message to every host within earshot, requesting the address associated with a host name. b-node has two shortcomings: broadcast traffic is undesirable and becomes a significant user of network bandwidths, and TCP/IP routers don't forward broadcast messages, which restricts b-node operation to a single network segment.

• p-node (point-to-point node) Relies on WINS servers for NetBIOS name registration and resolution. Client computers register themselves with a WINS server when they come on the network. They then contact the WINS server with NetBIOS name resolution requests. WINS servers communicate using directed messages, which can cross routers, so p-node can operate on large networks. Unfortunately, if the WINS server is unavailable or if a node isn't configured to contact a WINS server, p-node name resolution fails.

• m-node (modified node) A hybrid mode that first attempts to register and resolve NetBIOS names using the b-node mechanism. If that fails, an attempt is made to use p-node name resolution. m-node was the first hybrid mode put into operation, but it has the disadvantage of favoring b-node operation, which is associated with high levels of broadcast traffic.

• h-node (hybrid node) A hybrid mode that favors the use of WINS for NetBIOS name registration and resolution. When a computer needs to resolve a NetBIOS name, it first attempts to use p-node resolution to resolve a name via WINS. Only if WINS resolution fails does the host resort to b-node to resolve the name via broadcasts. Because it typically results in the best network utilization, h-node is the default mode of operation for Microsoft TCP/IP client computers configured to use WINS for name resolution. Microsoft recommends leaving TCP/IP client computers in the default h-node configuration.

Exam Alert: Configuring the Node Type

If you're using DHCP to provide TCP/IP configuration information to your clients, you can use DHCP Option 46 "WINS/NBT Node Type" to configure the node type in use. Additionally, DHCP Option 44 is used to configure WINS servers to be used by your clients.

The Method WINS Uses to Resolve a Name

The time might come when you need to understand exactly how WINS registers and resolves a name. (Because h-node is not only the default but also the recommended configuration, we will restrict our discussion to the h-node name resolution.) When a WINS client computer configured for h-node needs to resolve a host name, it goes through the following steps:

1.	It checks its NetBIOS name cache. If the name is found, it returns it.
2.	It queries the WINS server. If the name is found, it returns it.
3.	It issues a broadcast to find the host on the local network. If the name is found, it returns it.
4.	It looks for the lmhosts file to check for an entry. If the name is found, it returns it.
5.	It looks for the hosts file to check for an entry. If the name is found, it returns it.
6.	It queries the DNS server for the entry. If the name is found, it returns it.
7.	If all these methods fail, the WINS client computer issues an error message saying that it can't communicate with the host.

Although networks can be organized using a mixture of node types, Microsoft recommends against it. b-node client computers do not receive p-node directed messages, and p-node client computers ignore b-node broadcasts. Therefore, it is conceivable that two client computers could be established with the same NetBIOS name.

If WINS is enabled on a Windows XP or Windows 2000 computer, the system uses h-node by default. Without WINS, the system uses b-node by default. Non-WINS client computers can access WINS through a WINS proxy, which is a WINS-enabled computer that listens to name query broadcasts and then queries the WINS server on behalf of the requesting client computer.

Exam Alert: Registering with WINS

When your Windows client computer enters the network, it registers with WINS so that other Microsoft client computers can resolve its name to an address. For the exam, you should be aware that although a WINS proxy server can be used to resolve names for hosts that have registered with WINS, it can't be used to register with WINS. You need access to the WINS server to successfully register.

To see which node type is configured on a Windows XP computer, follow the steps outlined in Step by Step 4.4.

Step By Step

4.4. Identifying the NetBIOS Node Type

1.	Open a command prompt by selecting Start, Programs, Accessories, Command Prompt.
2.	At the command prompt, type ipconfig/all. You will get a result similar to the one shown in Figure 4.16. The node type is indicated to the right of the heading Node Type. In this example, the machine is running in h-node, the default for Windows XP and Windows 2000.

Next, let's look at the best way to manage and monitor WINS and manage your new WINS server.