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Chapter Overview

Understanding Windows Name Resolution

Using WINS

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Understanding Windows Name Resolution

Internet Protocol (IP) addresses are easily handled by computers but are difficult for people to remember.

Naming systems create user-friendly identifiers for computers and other network elements.

The naming system used by Microsoft Windows is based on Network Basic Input/Output System (NetBIOS).

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Understanding Windows Name Resolution (Cont.) A NetBIOS name is 16 characters long with 15

usable characters. You assign a NetBIOS name when you install

the operating system. After adopting Transmission Control

Protocol/Internet Protocol (TCP/IP) as the default networking protocol, Microsoft implemented standards that define the use of NetBIOS Over TCP/IP (NetBT).

These standards call for a mechanism that can resolve NetBIOS names into IP addresses.

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Understanding Windows Name Resolution (Cont.)

Windows has introduced the following NetBIOS name resolution mechanisms over the years, and all are available in Microsoft Windows 2000: NetBIOS name cache Network broadcasts LMHOSTS files Windows Internet Name Service (WINS) Active Directory service

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Understanding Windows Name Resolution (Cont.) Early versions of Microsoft Windows NT relied

on network broadcasts and LMHOSTS files for name resolution.

Windows NT 4 used WINS for NetBIOS name resolution.

Windows 2000 uses Active Directory for name resolution, which relies on the Domain Name System (DNS) to handle name registration and resolution tasks.

Microsoft Windows 2000 Server includes a WINS server to support computers on the network that run earlier versions of Windows.

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Understanding the NetBIOS Name Cache All Windows computers maintain a cache of

NetBIOS names they have recently resolved, and their equivalent IP addresses.

The computer checks the NetBIOS name cache before using another name resolution mechanism.

The cache is stored in memory. The cache is emptied each time the computer is

restarted. To view the NetBIOS name cache, you type

nbtstat -c at a command prompt, and then press Enter.

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Understanding Broadcast Name Resolution

When WINS servers are not available, computers running pre–Windows 2000 operating systems use broadcast messages to resolve NetBIOS names into IP addresses.

There are two main problems with the broadcast name resolution method: Broadcasts are limited to the local network. This method generates an excessive number of

broadcast transmissions on the network.

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Using LMHOSTS Files A HOSTS file is a text file containing a list of

host names and their equivalent IP addresses. A computer running TCP/IP uses a HOSTS file to

discover the IP address associated with a host name.

An LMHOSTS file uses the same concept for NetBIOS names.

The LMHOSTS files method is superior to the broadcast method because it is fast, it does not generate any network traffic, and it can resolve the NetBIOS name of a computer anywhere on a network.

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Using LMHOSTS Files (Cont.) LMHOSTS files have two shortcomings:

Someone must manually update the LMHOSTS file when the network changes.

Each computer must have its own copy of the file.

An LMHOSTS file consists of entries containing NetBIOS names and their corresponding IP addresses, such as 192.168.94.97 rhino 192.168.94.123 popular 192.168.94.117 localserv

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LMHOSTS Keywords

You can create different types of entries in an LMHOSTS file with the following keywords that perform special functions: \0xnn: provides support for nonprinting

characters in NetBIOS names #BEGIN_ALTERNATE: used to group multiple

#INCLUDE statements #END_ALTERNATE: used to mark the end of

an #INCLUDE statement grouping

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LMHOSTS Keywords (Cont.) #DOM:<domain>: part of the computer

name-to-IP-address mapping entry that indicates that the IP address belongs to a domain controller in the domain specified by <domain>

#INCLUDE <filename>: forces the system to seek the specified <filename> and parse it as if it were local

#MH: part of the computer name-to-IP-address mapping entry that defines the entry as a unique name that can have more than one address

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LMHOSTS Keywords (Cont.)

#PRE: part of the computer name-to-IP-address mapping entry that causes the entry to be preloaded into the name cache

#SG: part of the computer name-to-IP-address mapping entry that associates that entry with a user-defined special (Internet) group specified by <name>

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Introducing WINS

WINS is a NetBIOS name server that runs as a service on computers running Microsoft Windows NT Server and Windows 2000 Server.

WINS enables client computers to resolve NetBIOS names into IP addresses by sending a single unicast message to the WINS server, rather than broadcast messages to the entire network.

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Registering Names Name registration is the process of

establishing NetBIOS names on the network and associating them with specific IP addresses.

For an LMHOSTS file, name registration occurs when the administrator manually creates the entries in the file.

For the network broadcast and WINS methods, name registration occurs when each computer on the network starts.

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Windows Node Types The NetBIOS name registration and resolution

mechanisms used by a computer running a pre–Windows 2000 operating system are determined by the system's node type. B node: uses only broadcasts for name registration

and resolution. P node: uses only NetBIOS name servers for name

registration and resolution. M node: uses only broadcasts for name registration.

For name resolution, uses broadcasts first and switches to NetBIOS name server if the broadcasts fail to resolve the name.

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Microsoft Node Types Microsoft has developed its own node

types. Modified B node: uses only broadcasts for

name registration. For name resolution, uses broadcasts first and

switches to an LMHOSTS file if broadcasts fail Default node type for a non–WINS client computer

H node: uses only NetBIOS name server (WINS) for name registration.

For name resolution, uses NetBIOS name servers first, and if that fails, switches to broadcasts

Default node type for a WINS client computer

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Microsoft Node Types (Cont.)

Microsoft enhanced H node: a variation of the H node that adds LMHOSTS files, DNS queries, and HOSTS files as fallbacks to the NetBIOS name servers (WINS) and broadcasts defined in the H node type

Computers running Windows NT and Windows 2000 can use all of these name resolution methods.

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Lesson Summary Computers running Windows use NetBIOS names

to identify themselves on the network. To use NetBIOS names on a TCP/IP network,

there must be a mechanism to resolve NetBIOS names into IP addresses.

There are several NetBIOS name resolution mechanisms, including a NetBIOS name cache, network broadcasts, LMHOSTS files, WINS, and, for computers running Windows 2000, Active Directory.

Windows 2000 Server includes a WINS server to support pre–Windows 2000 clients.

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Using WINS

System administrators should know The purpose and function of WINS and

name registration How to install a WINS server How to configure a WINS client How to provide support for non–WINS clients

by using static mappings and by configuring a WINS proxy agent

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Introduction to WINS A Windows 2000 network requires a way to resolve

NetBIOS names to IP addresses for client computers running Microsoft Windows 98 or Microsoft Windows NT 4.

WINS is an enhanced NetBIOS name server that registers NetBIOS computer names and resolves them into the IP addresses needed for TCP/IP communication.

WINS also provides a dynamic database that maintains mappings of computer names to IP addresses.

All WINS messages are sent as unicasts. This reduces network traffic and enables the client to communicate with a WINS server anywhere on the network.

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The WINS Name Resolution Process

1. The WINS client checks its NetBIOS name cache to see if there is an entry for the desired name.

2. If there is not, the client transmits a NAME QUERY REQUEST unicast message to its primary WINS server.

3. The WINS server searches its database, and then returns the IP address to the WINS client in a POSITIVE NAME QUERY RESPONSE message.

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The WINS Name Resolution Process (Cont.)

4. If the requested name is not in the WINS server's database, the WINS server sends a NEGATIVE NAME QUERY RESPONSE message to the client.

5. If the client receives no response from the WINS server, it switches to the secondary WINS server.

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The WINS Name Registration Process When a WINS client computer is started, it

registers its NetBIOS name and IP address by sending a NAME REGISTRATION REQUEST message directly to its primary WINS server.

If the WINS server is available and another WINS client has not registered the name already, the WINS server returns a POSITIVE NAME REGISTRATION RESPONSE message to the client.

The WINS server also stores the client's NetBIOS name-to-IP-address mapping in its database.

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WINS Name Renewal

WINS servers register all NetBIOS names for a specified interval, the Time to Live (TTL). By default, the TTL is six days.

WINS clients must renew their NetBIOS names or their leases will expire.

Each time a WINS client computer restarts and registers its name with the WINS server, the TTL interval is reset.

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WINS Name Renewal (Cont.) If a client remains logged on continuously

for half of the TTL, it begins transmitting NAME REFRESH REQUEST messages to the WINS server.

The WINS server replies with one of the following messages: POSITIVE NAME REFRESH RESPONSE: resets

the TTL timer NEGATIVE NAME REFRESH RESPONSE: cancels

the name registration and forces the client to register a different NetBIOS name

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WINS Name Release When a WINS client computer shuts down,

the computer transmits a NAME RELEASE REQUEST message to the WINS server.

The WINS server responds with one of the following messages: POSITIVE NAME RELEASE RESPONSE: indicates

that the server has successfully released the name

NEGATIVE NAME RELEASE RESPONSE: occurs only when the server's record shows a different IP address than that of the requesting client

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Installing a WINS Server WINS is not installed by default. You can install WINS when you install

Windows 2000 Server, or you can install it later by using Add/Remove Programs in Control Panel.

A WINS server should be configured with a static IP address, subnet mask, and default gateway; it should not use a Dynamic Host Configuration Protocol (DHCP) server to obtain these TCP/IP settings.

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The Windows Components Page in the Windows Components Wizard

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Selecting WINS in the Networking Services Dialog Box

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The WINS Server After you install the WINS service on a

Windows 2000 Server computer, you should configure the server as a WINS client, with itself as the WINS server.

When you install WINS, the WINS snap-in is added to the Administrative Tools program group.

You can use this snap-in to view, configure, and manage the WINS servers on your network.

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The WINS Snap-In

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Configuring a Windows 2000 WINS Client Although Windows 2000 does not need WINS

to access resources on other computers running Windows 2000, it does need WINS to access resources on computers running earlier versions of Windows.

You must also configure the WINS server to be a client of itself.

You use the Network And Dial-Up Connections application in Control Panel to configure a computer running Windows 2000 to function as a WINS client.

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The Internet Protocol (TCP/IP) Properties Dialog Box

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The WINS Tab in the Advanced TCP/IP Settings Dialog Box

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Supporting Non–WINS Clients

In a WINS environment, you can provide support for non–WINS clients in two ways: By using static mappings By configuring a WINS proxy agent

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Using Static Mappings On a network that includes non–WINS

clients, you can configure a static NetBIOS name-to-IP-address mapping for each non–WINS client.

This ensures that WINS clients can resolve the NetBIOS names of non–WINS client computers.

You use the WINS console on the WINS server to configure a static mapping for non–WINS clients.

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The New Static Mapping Dialog Box

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Configuring a WINS Proxy Agent

A WINS proxy agent is a specially configured WINS client computer that listens for broadcast name registration and resolution messages from non–WINS clients, and then forwards these messages to a WINS server.

To configure a WINS proxy agent, on a WINS client computer, change the EnableProxy registry entry value to 1, and then restart the computer.

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Lesson Summary WINS is a NetBIOS name server that registers

NetBIOS computer names and resolves them into IP addresses.

WINS uses unicast transmissions, which reduce network traffic.

WINS is included with Windows 2000 to support clients running earlier versions of Windows.

Static mappings enable WINS clients to resolve NetBIOS names of non–WINS computers.

A WINS proxy agent relays broadcast name registration and resolution messages to a WINS server.