Configuring NetBIOS Name Resolution

Configuring NetBIOS Name Resolution

Some clients require NetBIOS names to communicate with other hosts on a network. A NetBIOS name is a 16-character name where the first 15 characters identify a unique host and the 16th character identifies a service or application running on the host, such as the Workstation or Server service.

As with domain names, NetBIOS names must be resolved to an IP address before two hosts can communicate. There are a number of methods available for name resolution and the method employed will depend on the environment.

The three standard ways of resolving NetBIOS names to IP addresses are through a local broadcast, using the local cache, or by using a NetBIOS name server (such as a WINS server). With a local broadcast, a broadcast is sent out on the network requesting the IP address of a specific host. One of the disadvantages of this method is the increase in traffic. All hosts maintain a local cache that can be used for name resolution. Each time a host resolves a NetBIOS name to an IP address, the record is added to the local cache and remains valid for 10 minutes. By default, all clients check their local cache before using any of the other resolution methods available. The third option is to use a NetBIOS name server to resolve names to IP addresses.

In a Microsoft environment, several other methods for resolving names are also available, such as DNS servers, HOSTS files, and LMHOSTS files.

Depending on the requirements of an environment, clients can be configured to use a single method for name resolution or they can use a combination of methods. The exact method a client uses to resolve NetBIOS names is determined by its node type. For example, if a client is configured as an M-Node, it attempts to resolve a NetBIOS name by first performing a local broadcast. If this is unsuccessful , it then tries to resolve the name using a NetBIOS name server. You can check the node type a client is configured for by typing ipconfig /all at the command prompt (see Figure 6.9). The node type can be changed via the local Registry. Table 6.2 summarizes the four node types.

Figure 6.9. Checking the node type using the ipconfig command from the command prompt.

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Remember that before performing a broadcast or contacting a WINS server, the host attempts to resolve a NetBIOS name using its local cache.


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Be prepared to encounter exam questions pertaining to the NetBIOS node types. Make sure you are familiar with which methods of resolution are used for each type and in what order.


Table 6.2. Node Type s

Node Type

Description

B-node

A broadcast is used for NetBIOS name registration and resolution.

P-node

A NetBIOS name server is used for name registration and resolution.

M-node

A broadcast is attempted first for name resolution. If this method fails, a NetBIOS name server is contacted.

H-node

A NetBIOS name server is attempted first for name resolution. If this fails, a broadcast is used.

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A Windows 2000 client that is configured as a DHCP client automatically uses H-node for NetBIOS name resolution. This means the client will attempt to resolve NetBIOS names using a WINS server first before using a local broadcast (after checking the local cache). The client resolves names in the following order: local cache, WINS, broadcast, LMHOSTS, HOSTS, and DNS. A useful mnemonic for remembering this order is: Can We Buy Large Hard Drives?


LMHOSTS Files

As already mentioned, one of the ways that NetBIOS names can be resolved is through the use of a text file known as an LMHOSTS file . One of the benefits of using an LMHOSTS file is that entries from the file can be preloaded into the local cache to facilitate name resolution (because this is the method a client will use to resolve a NetBIOS name). So if a client cannot resolve a NetBIOS name using any of the previous methods, clients can parse the LMHOSTS file to determine whether a record exists.

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For clients to resolve names using an LMHOSTS file, they must be configured to do so (refer to the "Configuring WINS Clients" section for more information).


The LMHOSTS file can be found in the %SYSTEMROOT%\system32\drivers\etc directory. By default, the file is named LMHOSTS.SAM and must be renamed LMHOSTS before it will work. Figure 6.10 provides an example of the contents of an LMHOSTS file. When configuring records within the file, there are several directives that can be used, as outlined in Table 6.3.

Figure 6.10. A sample LMHOSTS file.

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Table 6.3. Predefined LMHOSTS Directive s

Predefined Keyword

Description

#Pre

Defines which entries within the file should be loaded into the local cache.

#DOM:domain_name

Indicates the record of a domain controller.

#Begin_Alternate #End_Alternate

Specifies a list of other locations for an LMHOSTS file.

#include

Loads entries from a separate LMHOSTS file separate from the default file on the local computer. This option is most often used to specify a centrally located LMHOSTS file.

#MH

Adds multiple entries for a multihomed computer.

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Be sure you are familiar with the different directives that can be used within an LMHOSTS file and their purposes.




Windows 2000 Network Infrastructure Exam Cram 2 (Exam 70-216)
MCSE Windows 2000 Network Infrastructure Exam Cram 2 (Exam Cram 70-216)
ISBN: 078972863X
EAN: 2147483647
Year: 2005
Pages: 167

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