module 3: resolving namesstargate.inf.elte.hu/~pepe/corvinus/2277/5943303.pdf · lesson:...

Contents

Overview 1

Multimedia: Introduction to the Name Resolution Process 2

Lesson: Viewing Names on a Client 3

Lesson: Configuring Host Name Resolution 13

Lesson: Configuring NetBIOS Name Resolution 20

Lab: Resolving Names 31

Module 3: Resolving Names

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Module 3: Resolving Names iii

Instructor Notes This module provides students with the knowledge and ability to resolve names.

After completing this module, students will be able to:

! Describe the name resolution process. ! View names on a client. ! Configure host name resolution. ! Configure network basic input/output system (NetBIOS) name resolution. ! Resolve names.

To teach this module, you need the following materials:

! Microsoft® Office PowerPoint® file 2277c_03.ppt ! The multimedia presentation Introduction to the Name Resolution Process

It is recommended that you use PowerPoint 2002 or later to display the slides for this course. If you use PowerPoint Viewer or an earlier version of PowerPoint, some of the features of the slides may be displayed incorrectly.

To prepare for this module:

! Read all of the materials for this module. ! Complete all practices and the lab. ! Practice demonstrating all procedures on the How To pages. ! Review the multimedia presentation Introduction to the Name Resolution

Process. ! Review prerequisite courses and modules.

Presentation: 1 hour 30 minutes Lab: 15 minutes

Required materials

Important

Preparation tasks

iv Module 3: Resolving Names

How to Teach This Module This section contains information that will help you to teach this module.

Practices and Labs Explain to the students how the practices and labs are designed for this course. A module includes two or more lessons. Most lessons include a practice. After completing all of the lessons for a module, students finish the module with a lab.

This module does not include instructor demonstrations, but you should demonstrate many of the administrative tasks as you teach them. After you have covered the contents of the topics, explain that a practice will give students a chance for hands-on learning of all the tasks discussed in the lesson.

At the end of each module, the lab enables the students to practice the tasks that are discussed and applied in the module.

Using a scenario that is relevant to the job role of the students, the lab gives a set of instructions in a two-column format. The left column provides the task (for example, �Create a group�). In the right column are specific instructions that the students will need to perform the task (for example, �From Active Directory Users and Computers, double-click the domain node�).

An answer key for each lab exercise is located on the Student Materials CD, in case the students need step-by-step instructions to complete the lab. They can also refer to the practices and How To pages in the module.

Practices

Labs

Module 3: Resolving Names v

Multimedia: Introduction to the Name Resolution Process This section describes the instructional methods for teaching this presentation.

! The multimedia files are installed on the instructor computer. To open a multimedia presentation, click the animation icon on the slide for that multimedia presentation.

! Explain that this multimedia presentation provides a visual and high-level overview for the name resolution process. The details of name resolution are provided on the topic and How To pages.

! Estimated time required for the multimedia presentation is 5 minutes.

Lesson: Viewing Names on a Client This section describes the instructional methods for teaching this lesson.

! Define name resolution and the name resolution service. ! Describe how names are mapped to Internet Protocol (IP) addresses. Refer

to the slide. ! Discuss the characteristics of name resolution.

! Define name, host name, and fully qualified domain name (FQDN). ! Explain the purpose of host names. ! Explain how host names are used with Domain Name System (DNS)

suffixes to create an FQDN. Refer to the slide. ! Discuss the characteristics of a host name. ! Provide examples of host names, DNS suffixes, and FQDNs. ! Explain that the trailing period (.) at the end of an FQDN represents the root

location in the tree and is neither required nor often used in practice.

! Define NetBIOS names. ! Explain the purpose of NetBIOS names. ! Discuss the characteristics of NetBIOS names. ! Provide examples of NetBIOS names.

! Direct the students to complete the following practice tasks:

• View host name and Primary DNS Suffix by using the ipconfig command and the hostname command.

• View the NetBIOS name of a computer by using the nbtstat command.

• View the NetBIOS name of a remote computer by using its IP address and the nbtstat command.

• View the computer name by using the System properties. ! Reconvene class after all students have completed the practice and discuss

the results of the practice.

How Names Are Mapped to IP Addresses

What Are Host Names?

What Are NetBIOS Names?

Practice: Viewing Names on a Client

vi Module 3: Resolving Names

Lesson: Configuring Host Name Resolution This section describes the instructional methods for teaching this lesson.

! Define host name resolution. ! Describe how host names are resolved to IP addresses. ! Briefly describe the standard methods for resolving host name resolution.

• This lesson provides in-depth topics on each of the standard methods.

Systems administrators may spend a significant portion of their time ensuring that the host name resolution process works correctly. Be sure to emphasize the importance of this process.

! Define client resolver cache and negative cache entries. ! Explain the purpose of the client resolver cache. ! Explain the purpose of the negative cache entries. ! Explain the information sources for the client resolver cache. ! Discuss the characteristics of the client resolver cache, including Time to

Live (TTL). ! Provide examples of the client resolver cache. ! An example is provided in the slide, which illustrates the results of the

ipconfig /displaydns command. ! Demonstrate the use of the ipconfig /displaydns and the ipconfig /flushdns

commands.

! Define the Hosts file. ! Explain the purpose of a Hosts file. ! Discuss the characteristics of a Hosts file. ! Provide examples of Hosts files.

• An example is provided in the slide, which illustrates the contents of the sample Hosts file that can be found in the %Systemroot%\System32\ Drivers\Etc\ folder and is named Hosts.


• Flush the client resolver cache.

• Preload the client resolver cache.

• Verify that the entry that the student added appears in the client resolver cache.

! Reconvene class after all students have completed the practice and discuss the results of the practice.

Host Name Resolution Process

Note

Client Resolver Cache

Hosts File

Practice: Configuring Host Name Resolution

Module 3: Resolving Names vii

Lesson: Configuring NetBIOS Name Resolution This section describes the instructional methods for teaching this lesson.

! Define NetBIOS name cache. ! Explain the purpose of the NetBIOS name cache. ! Discuss the characteristics of the NetBIOS name cache, including the

NetBIOS name type and TTL (or Life). ! Provide examples of the NetBIOS name cache.

• An example is provided in the slide, which illustrates name, type, host address, and Life (in seconds).

! Define NetBIOS name resolution. ! Refer to the slide to describe how NetBIOS names are resolved to IP

addresses.

• The slide illustrates the default order of the resolution methods, in which the client is configured to query a Microsoft Windows® Internet Naming Service (WINS) server and to use an Lmhosts file. The sequence of these resolution methods is configurable based on multiple conditions in each unique environment.

! Briefly describe the methods for resolving NetBIOS names.

• This lesson provides in-depth information on each of the methods.

! Define local broadcasts. ! Explain the purpose of broadcasts. ! Discuss the characteristics of broadcasts. ! Provide examples of broadcasts.

• An example is provided in the slide, which illustrates how a local broadcast is sent and answered, in addition to how a broadcast will not pass through the router to a resource on a remote network.

! Ask the students, �Why are broadcasts not used often today?�

• Answers may include, �There is too much traffic.�

NetBIOS Name Cache

NetBIOS Name Resolution Process

Local Broadcasts

viii Module 3: Resolving Names

! Define Lmhosts file. ! Explain the purpose of an Lmhosts file. ! Discuss the characteristics of an Lmhosts file. ! Describe predefined keywords (such as #PRE, #DOM,

#BEGIN_ALTERNATE, #BEGIN_END, and #INCLUDE). ! Provide examples of Lmhosts files.

• An example is provided in the slide, which illustrates the contents of the sample Lmhosts file that can be found in the %Windir%\System32\ Drivers\Etc\ folder and is named Lmhosts.

! Demonstrate the use of the nbtstat command and discuss how the command can be used for troubleshooting.


• View the NetBIOS name cache.

• Preload a NetBIOS name cache by using an Lmhosts file.

• Release the NetBIOS name cache and reload entries from the Lmhosts file.

! Reconvene class after all students have completed the practice and discuss the results of the practice.

Lab: Resolving Names Remind the students that they can review the module for assistance in completing the lab. Tell students that a detailed answer key for each lab is provided in the Labdocs folder on the Student Materials CD.

Lmhosts File

Practice: Configuring NetBIOS Name Resolution

Module 3: Resolving Names 1

Overview

*****************************ILLEGAL FOR NON-TRAINER USE******************************

Name resolution is the process of translating user-friendly names into numerical Internet Protocol (IP) addresses. Although it is typically easier for end users to use intuitive names for connecting to resources, the underlying Transmission Control Protocol/Internet Protocol (TCP/IP) architecture requires that an IP address be used to establish the actual communication. Name resolution provides a background process for resolving names to IP addresses.

Two types of names can be resolved:

! Host names ! Network basic input/output system (NetBIOS) names

After completing this module, you will be able to:

! Describe the name resolution process. ! View names on a client computer. ! Configure host name resolution. ! Configure NetBIOS name resolution.

Introduction

Objectives

2 Module 3: Resolving Names

Multimedia: Introduction to the Name Resolution Process


To start the Introduction to the Name Resolution Process presentation, open the Web page on the Student Materials CD, click Multimedia, and then click the title of the presentation.

At the end of this presentation, you will be able to:

! Explain what a host name is. ! Explain what a NetBIOS name is. ! Describe how the name resolution process works.

! Name resolution is a critical component of the TCP/IP network

communication process. ! Two types of names are used in a TCP/IP network: host names and

NetBIOS names. ! Host names and NetBIOS names are display names that users employ to

identify and access resources. Computers, however, use IP addresses to connect to each other. Therefore, display names must be resolved to IP addresses to allow users to access resources on the network.

File location

Objectives

Key points


Lesson: Viewing Names on a Client


Two types of names are used on a TCP/IP network: host names and NetBIOS names. As a systems administrator, you will need to know how to view and change both of these types of names to successfully manage your network.

After completing this lesson, you will be able to:

! Describe how names are mapped to IP addresses. ! Explain what host names are. ! Explain what NetBIOS names are. ! View names on a client.

Introduction

Lesson objectives


How Names Are Mapped to IP Addresses


Name resolution is the process of having software automatically translate between alphanumeric names (such as Server1 or Computer44) and numerical IP addresses (such as 192.168.1.200 or 10.0.0.1). IP addresses are more difficult for users to work with than names, but they are necessary for TCP/IP communications.

A name resolution service provides a systematic process for converting (also called resolving) display (or alphanumeric) names to an IP address. Name resolution services also allow TCP/IP hosts to query for specific types of network resources or services, such as a domain controller or a Simple Mail Transfer Protocol (SMTP) messaging server. They also allow TCP/IP hosts to receive the name and IP address of the computers that provide that resource or service. Microsoft® Windows® Internet Name Service (WINS) and Domain Name System (DNS) are name resolution services.

To enable users to access resources, there must be a method to match names to IP addresses. With this matching method, a user can request a resource by using a name like Server1, and the computer can determine that Server1 is associated with the IP address 192.168.1.200. The computer can connect to the resource you call Server1 when it understands that Server1 is IP address 192.168.1.200.

The process for name resolution is similar to finding a telephone number by using a telephone book. If you want to call your friend on the phone, you look for your friend�s name in the telephone book to find the telephone number. The telephone book provides you with the telephone number associated with your friend�s name. You can then use the number to telephone your friend.

Definitions

Process


Important characteristics of name resolution are as follows:

! A host name may map to more than one IP address for a particular name. For example, three separate servers may host a replica of the same Web site and be accessed with the same name. Each server must have a unique IP address, so one name may be mapped to more than one IP address.

! There are multiple methods for resolving host names and multiple methods for resolving NetBIOS names. These methods have evolved over time to meet various needs.

! Applications and services determine which name resolution method should be used.

! The configuration of the operating system determines how the name resolution process resolves the name.

Characteristics of name resolution


What Are Host Names?


A name is the identifier of your computer on the network.

A host name is the DNS name of a device on a network.

A fully qualified domain name (FQDN) is a DNS domain name that has been stated unambiguously to indicate with absolute certainty its location in the domain namespace tree.

Host names are used to locate computers on the network. To enable a computer to contact another computer by using a host name, the host name must either appear in the Hosts file or be known by a DNS server. For most computers running Microsoft Windows Server� 2003 or Microsoft Windows XP, the host name and the NetBIOS name are the same.

Host names provide the capability for name resolution on the Internet. A host name is part of an FQDN, which uses a hierarchical structure. Host names are typically part of the DNS namespace that allows you to access resources in a DNS structure.

Host names are part of the DNS namespace; they allow a client to locate resources worldwide through the global DNS namespace.

A host name can exist as a single-part name, or it can be used with the suffix to create the identifier for a resource on a TCP/IP network. The host name and suffix are known together as the FQDN.

In an FQDN, such as server1.training.contoso.msft, the host name portion of the FQDN is server1. The latter part, training.contoso.msft, is known as the suffix. Together, the host name (server1) and the suffix (training.contoso.msft) reference a single, specific resource on a TCP/IP network. The suffix is essential to the host name because it allows two identical host names to exist on the network without conflict. The FQDN server1.training.contoso.msft can exist on the same network with server1.contoso.msft. The suffix differentiates between the two names.

Definitions

Purpose of host names

Host name and suffix


For more information about DNS, refer to Module 4, �Resolving Host Names by Using Domain Name System (DNS),� in Course 2277, Implementing, Managing, and Maintaining a Microsoft Windows Server 2003 Network Infrastructure: Network Services.

When the administrator installs the operating system, the computer identifier and DNS suffix are combined to create the FQDN. If necessary, the host name and suffix can be modified on most computers

Because so many networking elements rely on the DNS namespace, it is important to plan the host names and suffixes that will be used on your network. An implementation plan will help ensure that a naming scheme can uniquely identify hosts on the network and that there are no naming conflicts.

Host names are used in virtually all TCP/IP environments. The following list describes the characteristics of a host name:

! A host name is an alias that an administrator assigns to a device that is connected to a TCP/IP network.

! Although a Windows Server 2003 and Windows XP host name will by default be set to the same name as the NetBIOS name, the host name can differ from the NetBIOS computer name.

! The host name can be any 255-character string. ! Although a host can map to only one host name, it is also possible to have

several host names map to a single host. Name resolution methods, such as the Hosts file or DNS, can have multiple host names that will map to the IP address of the same host. For example, the host den-srv1.contoso.msft could have entries in DNS for both DEN-Srv1.contoso.msft and www.contoso.msft. Either name will resolve to the IP address of DEN-Srv1.contoso.msft.

! It is possible for one host name to resolve to more than one IP address. For example, three identical Web servers could all be identified in DNS by using the name www.contoso.msft. When a client attempts to connect to www.contoso.msft through a Web browser, three IP addresses would be returned from the DNS query. This procedure can be used as a very basic form of load balancing.

! A host name can be used in place of an IP address when you are using the Ping command or other TCP/IP tools. The name will first be resolved to an IP address, and then a communication attempt will be made by using the IP address.

! To resolve a name, a host name and its corresponding IP address must be configured in a database on a DNS server or in a Hosts file.

! The Hostname command displays the host name that is assigned to your system. By default, the host name is the same as the computer name of your Windows-based computer.

Note

Important

Characteristics of a host name


The following table shows examples of host names, DNS suffixes, and FQDNs.

Fully Qualified Domain Name (FQDN) Host name DNS suffix FQDN server1 training.contoso.msft server1.training.contoso.msft

server1 contoso.msft server1.contoso.msft

www microsoft.com www.microsoft.com

computer44 contoso.msft computer44.contoso.msft

In the illustration on the PowerPoint slide, notice that there is a trailing period (.) at the end of an FQDN. This trailing period represents the root location in the tree and is neither required nor often used in practice.

Examples

Note


What Are NetBIOS Names?


A NetBIOS name is an identifier that is used by NetBIOS services that are running on a computer. It is made up of a 15-character name plus a sixteenth character (byte) denoting the service.

NetBIOS names are used to identify resources in a NetBIOS network. NetBIOS names do not provide the capability for name resolution on the Internet, because NetBIOS names are single-part names and do not have hierarchical structure. The NetBIOS namespace is flat, which means that no suffixes are added to the NetBIOS name and that there is no way to differentiate two computers that have the same NetBIOS name. This means that each NetBIOS name in any one network must be unique. For example, if Server2 is the NetBIOS name of a computer in a NetBIOS network, the system will generate an error if two computers have the same name on the same network. Characteristics of NetBIOS names are as follows:

! NetBIOS names are used to support services that require NetBIOS. Windows Server 2003, Windows 2000, and Windows XP use DNS names for most functions, but a NetBIOS name resolution method must exist on any network that includes computers that are running earlier versions of Windows or applications that still depend on NetBIOS names.

! A NetBIOS name is an alias that is assigned to a computer by an administrator to identify a NetBIOS service running on a TCP/IP host.

! The NetBIOS name can differ from the host name. ! NetBIOS names are 15 or fewer characters in length, compared to 255 or

fewer characters for DNS host names. The host name and the NetBIOS name on a computer running Windows Server 2003 are generated together. If the host name is longer than 15 characters, the NetBIOS name is the first 15 characters of the host name.

! NetBIOS names must be unique on their networks.

Definition

Purpose of NetBIOS names

Characteristics of NetBIOS names


! When you start your computer, various services (such as the server service or the workstation service) register a unique NetBIOS name that is based on the computer name. The registered name is the 15-character NetBIOS name, plus a sixteenth character (byte) that uniquely identifies a service. For example, a server named DEN-SRV1 would register the NetBIOS name DEN-SRV1, with the sixteenth byte <20>, indicating that it is a file server.

Each character is one byte rendered in ASCII text, but the sixteenth character is normally rendered in hexadecimal notation rather than in ASCII text, so it is often referred to as the sixteenth byte rather than the sixteenth character.

! NetBIOS names are also registered for groups of computers that provide network services. For example, if DEN-DC1 is a domain controller, it will register the NetBIOS name DEN-DC1 and will also register names that identify its roles as a domain controller in the Contoso domain at the same time. This allows clients to search for all NetBIOS hosts that provide domain controller services in the Contoso domain, without the client knowing the actual names of the domain controllers.

! A NetBIOS name can be resolved if the name and IP address are stored either in a database on a WINS server or in an Lmhosts file. A broadcast can also resolve a NetBIOS name.

! The Nbtstat command displays the NetBIOS names that NetBIOS services use on your computer.

! The NetBIOS name is created while the operating system is being installed. When the computer name is created, the installation automatically creates both a host name and a NetBIOS name that are based on the computer name.

For example, suppose DEN-SRV2 is the NetBIOS name of the computer in the slide. The computer is running several NetBIOS services, including workstation, server, and messenger. Each of the services is associated with the same NetBIOS name (DEN-SRV2).

With computers running Windows Server 2003 operating systems, you can disable NetBIOS over TCP/IP for each network connection. This feature is intended for computers that use only host name registration and resolution techniques and communicate (by using the Client for Microsoft Networks and the File and Print Sharing for Microsoft Networks components) with other computers on which NetBIOS over TCP/IP is disabled.

Disabling NetBIOS over TCP/IP may cause NetBIOS-based applications to stop functioning as expected and may restrict certain clients from establishing a connection with Windows Sever 2003. Clients running operating systems such as Windows 95 and Microsoft Windows NT® 4.0 require NetBIOS over TCP/IP for accessing shared resources such as files and printers on computers running Windows Server 2003.

Note

Examples

Disabling NetBIOS over TCP/IP


Practice: Viewing Names on a Client


In this practice, you will view host names and NetBIOS names on a computer.

Ensure that the DEN-DC1 and DEN-SRV1 virtual machines are started.

! Prepare for this practice

• Log on to DEN-DC1 as Contoso\Administrator with a password of Pa$$w0rd.

! View host name and NetBIOS names

1. Click Start, point to All Programs, point to Accessories, and then click Command Prompt.

2. At the command prompt, type hostname and then press ENTER. What is the computer�s host name? DEN-DC1 ____________________________________________________________

3. At the command prompt, type ipconfig /all and then press ENTER. What is the Primary DNS Suffix? Contoso.msft ____________________________________________________________

4. At the command prompt, type nbtstat -n and then press ENTER. What is the NetBIOS name of the computer? DEN-DC1 ____________________________________________________________

Objective

Instructions

Practice


5. At the command prompt, type nbtstat -a 10.10.0.10 and then press ENTER. What is the NetBIOS name of the remote computer? DEN-SRV1 ____________________________________________________________

6. Click Start, point to Control Panel, and then click System. 7. Click the Computer Name tab. What is the full computer name?

DEN-DC1.contoso.msft ____________________________________________________________

8. Close all open windows.


Lesson: Configuring Host Name Resolution


Windows Server 2003 depends primarily on host name resolution for resolving the names of computers to IP addresses. Host name resolution can resolve a name by using the client resolver cache, DNS servers, and the Hosts file.

This lesson describes how you can use the client resolver cache and the Hosts file to resolve host names to IP addresses. Module 5, �Resolving Host Names by Using Domain Name System (DNS),� in Course 2277, Implementing, Managing, and Maintaining a Microsoft Windows Server 2003 Network Infrastructure: Network Services, covers how you can use a DNS server to resolve host names to IP addresses.


! Describe the host name resolution process. ! Explain what a client resolver cache is. ! Explain what a Hosts file is. ! Configure host name resolution.

Introduction

Note

Lesson objectives


Host Name Resolution Process


Host name resolution is the process of resolving a host name to an IP address.

The host name resolution process functions as follows:

1. An application or service passes a host name to the DNS client service. 2. The DNS client service searches the client resolver cache for the mapping

for host name to IP address. All entries into the Hosts file are preloaded into the client resolver cache.

3. If the DNS client service does not locate a mapping in the client resolver cache, the DNS client service forwards a host name query to a DNS server.

4. If the configured host name resolution methods fail, the configured NetBIOS name resolution methods are employed to attempt to resolve the name. This occurs only if the Host name is 15 or fewer characters long.

5. When the host name is found, the corresponding IP address is returned to the application.

The Microsoft implementation of TCP/IP uses the methods that are described in the following table when it employs the DNS client service to resolve host names to IP addresses.

Standard methods of resolution

Description

DNS client resolver cache

A cached storage location on the local computer where the DNS client service stores resolved mappings for host name�to�IP address.

DNS server A server that maintains a database of IP address/computer name (host name) mappings.

Hosts file A local text file in the same format as the 4.3 Berkeley Software Distribution (BSD) UNIX\Etc\Hosts file. This file matches host names to IP addresses.

Definition

Host name resolution process

Methods of host name resolution


Client Resolver Cache


The client resolver cache is a location in memory that stores host names that have recently been resolved to IP addresses. Host name�to�IP address mappings located in the Hosts file are automatically loaded into the client resolver cache.

Negative cache entries are host names entered into the cache that were queried but could not be resolved.

The client resolver cache is the first place that the DNS client looks for host name�to�IP address mappings. The client resolver cache resolves IP addresses quicker than the other host name resolution methods, such as the DNS server and the Hosts file methods. In addition, the client resolver cache creates no network traffic.

Negative cache entries are created automatically when a host name query fails to resolve the IP address for a particular name. By default, the failed name is cached for five minutes so that if the same failed name is queried again, the client does not query the DNS server but instead determines that the host name is not resolvable by checking the cache.

The local client resolver cache can include name information that is obtained from two possible sources:

! Hosts file If a Hosts file is configured locally, any host name�to�IP address mappings from that file are preloaded into the cache.

! Any resolved names Resource records obtained in answered responses from previous DNS queries are added to the cache and kept for a period of time based on the Time to Live (TTL). The TTL of a record indicates how long the record should be cached.

Definitions

Purpose of the client resolver cache

Purpose of negative cache entries

Information sources for the client resolver cache


The client resolver cache maintains resolved host name information, including the record name, TTL, and IP address.

Mappings for host names to IP addresses remain in the DNS resolver cache for a limited time. This means that if you need to resolve a host name, you can find the mapping in the client resolver cache. For example, if your applications are constantly resolving the same host names, the client resolver cache could quickly resolve the host name.

However, the mapping for a host name to an IP address is maintained for a period of time known as the Time to Live (TTL). Whether or not the name is accessed before the time period expires, the mapping is removed when the TTL expires. This helps keep the cache from growing too large and from maintaining mappings that may change and become invalid. The TTL will be determined by the DNS server that is authoritative for the resource record.

You can use the Ipconfig command to troubleshoot a problem with host name resolution.

You can use the command ipconfig /displaydns to view the host names that you have recently resolved. You can also use it to display names that have been negatively cached.

You can use the command ipconfig /flushdns to flush the resolver cache. You may want to flush the cache if you notice that it contains incorrect entries. Incorrect entries in the cache may be caused by network configuration changes (when a server�s IP address is changed) or a network error.

For example, if a client loses network connectivity to a DNS server and attempts to connect to DEN-Srv1.contoso.msft, the name resolution request will fail and an entry will be added to the cache indicating that the name cannot be resolved. If connectivity to the DNS server is restored, the client will still be unable to connect to DEN-Srv1.contoso.msft. This results from an entry in the cache indicating that the name does not exist. To correct this problem immediately, you could use the command ipconfig /flushdns to clear the cache immediately. Alternately, you could wait until the TTL of the record expires, at which point the entry will be automatically removed from the cache. Five minutes is the default TTL for entries that have been negatively cached.

Client resolver cache

Troubleshooting host name resolution


Hosts File


The Hosts file is a static local file that contains host name�to�IP address mappings. Address mapping from the Hosts file are automatically added to the client resolver cache.

You can use the Hosts file to preload permanent host name�to�IP address mappings into the client resolver cache. This decreases the response time for queries and reduces network traffic.

Characteristics of a Hosts file include the following:

! A single entry in the Hosts file consists of an IP address corresponding to one or more host names. The host name in the hosts file can be a single-part name such as Server1, or an FQDN such as server1.contoso.msft.

! A Hosts file must reside on each computer. The client resolver cache searches locally for the Hosts file.

! The Hosts file is found in the %Systemroot%\System32\Drivers\Etc\ folder and is named Hosts.

! When you create a host name�to�IP address mapping in the Hosts file and then save the Hosts file, the mapping is loaded into the client resolver cache. The host name mapping entry, from the Host file, does not contain a TTL period. The host name mapping will remain in the client resolver cache until it is removed from the Hosts file.

! The Hosts file is compatible with UNIX Hosts file.

The slide shows you the contents of a Hosts file. This sample Hosts file can be found in the %Systemroot%\System32\Drivers\Etc\ folder and is named Hosts. If you were to make entries to this Hosts file and then save it, those entries would be immediately loaded into your DNS client resolver cache.

Definition

Purpose of a Hosts file

Hosts file

Example


Practice: Configuring Host Name Resolution


In this practice, you will configure host name resolution by using the Hosts file.


! Prepare for this practice

• If necessary, log on to DEN-DC1 as Contoso\Administrator with a password of Pa$$w0rd.

! Configure host name resolution

1. On DEN-DC1, click Start, point to All Programs, point to Accessories, and then click Command Prompt.

2. At the command prompt, type ipconfig /flushdns and then press ENTER. 3. At the command prompt, type ping testserver and then press ENTER. Was

the name successfully resolved to an IP address? The name is not resolved to an IP address. ____________________________________________________________

4. On DEN-DC1, browse to c:\windows\system32\drivers\etc. Right-click the Hosts file and then click Open.

5. When prompted, choose Notepad and then click OK. 6. Add the following entry to the end of the file:

10.10.0.10 Testserver 7. From the file menu in Notepad, click Exit. When prompted, click Yes to

save changes to the file.

Objective

Instructions

Practice


8. At the command prompt, type ipconfig /displaydns and then verify that an entry appears for Testserver.

9. At the command prompt, type ping testserver and then press ENTER. Was the name successfully resolved to an IP address? The computer name resolves to 10.10.0.10. ____________________________________________________________



Lesson: Configuring NetBIOS Name Resolution


You can use the NetBIOS name cache, WINS server, broadcast, or Lmhosts file to resolve NetBIOS names to IP addresses.

This lesson describes how you can use the NetBIOS cache, broadcast, and Lmhosts file to resolve host name�to�IP address mappings. For more information about how to use a WINS server to resolve host name�to�IP address mappings, see Module 7, �Resolving NetBIOS Names by Using Windows Internet Naming Service,� in Course 2277, Implementing, Managing, and Maintaining a Microsoft Windows Server 2003 Network Infrastructure: Network Services.


! Explain what the NetBIOS name cache is. ! Describe the NetBIOS name resolution process. ! Explain what broadcasts are. ! Explain what an Lmhosts file is. ! Configure NetBIOS name resolution.

Introduction

Note

Lesson objectives


NetBIOS Name Cache


A NetBIOS name cache is a location in memory that stores NetBIOS names that have recently been resolved to IP addresses. This name cache includes names resolved through a WINS server, broadcast, or Lmhosts file. The NetBIOS name cache also stores name-to�IP address mappings that are preloaded from the Lmhosts file.

The NetBIOS name cache is the first place that the NetBIOS redirector searches for an IP address to map to a NetBIOS name. NetBIOS name cache resolves IP addresses more quickly than a WINS server, broadcast, or Lmhosts file, and it creates no network traffic.

In addition, you can preload the NetBIOS name cache with frequently used NetBIOS name�to�IP address mappings by using the Lmhosts file.

The NetBIOS name cache contains the NetBIOS names that the local computer has recently resolved and also the name resolution results. Name resolution is performed more quickly because the cached results are accessed for name resolution. However, name resolution data is limited to recently resolved names.

When a user initiates a NetBIOS name query by using an application or service, such as the net use command, the NetBIOS name resolution process begins. The NetBIOS name cache is checked for the NetBIOS name�to�IP address mapping of the destination host. The NetBIOS name cache contains the most recently resolved NetBIOS names. If the NetBIOS name is not found in the cache, the client that is running Windows attempts to determine the IP address of the destination host by using other methods.

Definition

Purpose of a NetBIOS name cache

NetBIOS name cache


For a command such as net use and other commands that call the server message block (SMB) protocol, Windows 2000, Windows XP, and Windows Server 2003 can employ either direct hosting over SMB or the traditional NetBIOS over TCP/IP. If both direct hosting and NetBIOS over TCP/IP are enabled, both methods are tried at the same time, and the first to respond is used. NetBIOS over TCP/IP will attempt to use NetBIOS name resolution. Direct hosting will use host name resolution.

After a NetBIOS name is resolved to an IP address, a mapping entry is made in the NetBIOS name cache and is given a refresh interval (or TTL) of 10 minutes. If the name in the NetBIOS cache is accessed within the TTL, the TTL is reset to 10 minutes. If the TTL is reached without the name being accessed, the mapping is removed from the NetBIOS name cache. When you view the NetBIOS name cache, the TTL appears as Life in seconds.

NetBIOS names can be one of two types: Unique or Group. A Unique NetBIOS name refers to a NetBIOS service hosted on an individual computer. A Group NetBIOS name refers to a NetBIOS service hosted on a group of computers. The following list contains common NetBIOS name registrations.

<computer_name>[00] Unique Workstation Service

<computer_name>[03] Unique Messenger Service

<computer_name>[20] Unique Server Service

<user_name>[03] Unique Messenger Service

<domain_name>[1D] Unique Master Browser

<domain_name>[1B] Unique Domain Master Browser

<domain_name>[00] Group Domain Name

<domain_name>[1C] Group Domain Controllers

[01h][01h]__MSBROWSE__[01h][01h] Group Master Browser

The following table illustrates examples of NetBIOS name�to�IP address mappings stored in a NetBIOS name cache. Notice the following:

! The Name column includes the sixteenth character that identifies the service that is registering the NetBIOS name.

! NetBIOS names are Unique. ! The Life column shows the number of seconds remaining before the

NetBIOS name is removed.

Name Type Host address Life (seconds) Server3 <20> Unique 192.168.1.156 515

Computer9 <20> Unique 192.168.1.101 430

Note

Example


NetBIOS Name Resolution Process


NetBIOS name resolution is the process of mapping a NetBIOS name to an IP address.

Administrators can custom-configure the sequence of steps in the NetBIOS name resolution process, but the default sequence is as follows:

1. When an application needs to resolve a NetBIOS name to an IP address, the application searches in the NetBIOS cache for a mapping.

2. If the NetBIOS cache does not resolve the NetBIOS name to an IP address, the WINS server is queried.

3. If the WINS server does not resolve the NetBIOS name to an IP address, a NetBIOS name query is sent to the local network as a broadcast.

4. If the broadcast does not resolve the NetBIOS name to an IP address, the local Lmhosts file is searched.

5. When the NetBIOS name is found, the corresponding IP address is returned to the application.

The NetBIOS node type is a configurable parameter that allows you to control the order in which NetBIOS names are resolved. The node can be configured to allow name resolution broadcasts to occur before your computer queries a WINS server, to disable name resolution broadcasts, or to disable WINS resolution. For more information on the NetBIOS node type, see Module 7, �Resolving NetBIOS Names by Using Windows Internet Naming Service,� in Course 2277, Implementing, Managing, and Maintaining a Microsoft Windows Server 2003 Network Infrastructure: Network Services.

Definition

NetBIOS name resolution process

Note


The Microsoft implementation of TCP/IP uses the NetBIOS redirector service to resolve host names to IP addresses. The table below lists methods for this process.

Standard methods of resolution

Description

NetBIOS name cache The cache contains the NetBIOS names that the local

computer has recently resolved.

NetBIOS name server A NetBIOS name server can provide centralized resolution of NetBIOS names to IP addresses. WINS is a NetBIOS name server.

Local broadcast The NetBIOS name query is broadcast onto the local network.

Methods of NetBIOS name resolution


Local Broadcasts


Local broadcasts are network messages sent from a single computer that are distributed to all other devices on the sending computer�s segment of the network. NetBIOS names can be resolved by using local broadcasts.

If the NetBIOS name is not resolved by the NetBIOS cache, the NetBIOS redirector can send a NetBIOS broadcast.

A NetBIOS client can issue a local broadcast requesting the IP address of the destination NetBIOS name. The host that owns the NetBIOS name replies with its IP address, and the host that initiated the broadcast can then connect to the host that owns the NetBIOS name.

You can reduce broadcast traffic by using a WINS server rather than local broadcasts to resolve NetBIOS names. In addition, routers are not normally configured to forward NetBIOS broadcasts, which limits NetBIOS name resolution to a single network segment.

The NetBIOS redirector sends out a local broadcast. If the resource is on the local network, the broadcast is answered and an IP address is returned. If the resource is on a remote network, the broadcast will not pass through a router. Therefore, the query will fail and no IP address will be returned.

Definition

Purpose of NetBIOS broadcast

Note

Example


Lmhosts File


An Lmhosts file is a local text file that maps NetBIOS names (commonly used for computer names) to IP addresses.

The Lmhosts file is a static file on the local computer that can aid in the resolution of a NetBIOS name. You can add NetBIOS name�to�IP address mappings to the file to support NetBIOS name resolution. You can also preload mappings into the NetBIOS name cache.

The Lmhosts file can be configured to be read by Microsoft clients as an additional means of resolving NetBIOS names. The Lmhosts file is a static ASCII text file that is used to resolve the NetBIOS names of NetBIOS-based computers. The Lmhosts file has the following characteristics:

! A single entry consists of one NetBIOS name and its corresponding IP address. The entry must match the NetBIOS name of the target computers or the alias will fail.

! An Lmhosts file must reside on each computer. ! The location of the Lmhosts file must be in the %Systemroot%\System32\

Drivers\Etc\ folder. By default, no Lmhosts file exists. A sample file named Lmhosts.sam is in the %Systemroot%\System32\Drivers\Etc\ folder. If you use this file as your Lmhosts file, be sure to remove the .sam file extension when saving your initial changes.

! Entries in the Lmhosts file that include the #PRE keyword will be preloaded into the NetBIOS name cache. The NetBIOS name mappings that have the #PRE keyword will remain in the NetBIOS cache until the mappings that have the #PRE keyword are removed from the Lmhosts file and the NetBIOS name cache is purged and reloaded.

Definition

Purpose of the Lmhosts file

Lmhosts file


An Lmhosts file contains predefined keywords that enable you to manage the mappings in the Lmhosts file. Each is prefixed with a pound sign (#). The following table lists and describes the Lmhosts keywords.

Predefined keyword Description #PRE Causes the system to preload the specified entries into the

name cache. Preloaded entries reduce network traffic because names are resolved from the cache rather than through a broadcast or through querying a WINS server. Entries with a #PRE tag are loaded either automatically at initialization or manually by typing nbtstat -R at a command prompt.

#DOM:[domain_name] Facilitates domain activity, such as logon validation over a router, account synchronization, and browsing.

#BEGIN_ALTERNATE#END_ALTERNATE

Defines a redundant list of alternate locations for Lmhosts files. The recommended way to include remote files is by using a Universal Naming Convention (UNC) path to ensure access to the file. The UNC names, with a proper IP address to NetBIOS name mapping, must exist in the Lmhosts file.

#INCLUDE Loads and searches NetBIOS entries in a separate file from the default Lmhosts file. Typically, an #INCLUDE file is a centrally located and shared Lmhosts file.

The NetBIOS name cache and file are always read sequentially. Add the most frequently accessed computers to the top of the list. Add the entries tagged with #PRE near the bottom because they will not be accessed again after TCP/IP initializes. For more information about the Lmhosts file, read the instructions in the Lmhosts file or see the Windows Server 2003 Help documentation.

The slide shows you the contents of an Lmhosts file. This sample Lmhosts file can be found in the %Systemroot%\System32\Drivers\Etc\ folder and is named Lmhosts.sam.

Predefined keywords

Note

Example


You can use the Nbtstat command to troubleshoot problems with NetBIOS name resolution. The most common Nbtstat command-line options are listed in the following table.

Command syntax Explanation nbtstat -c Displays the names that have recently been resolved by using

NetBIOS name resolution.

nbtstat �n Displays the names that your computer has registered on the network.

Nbtstat -R Purges the NetBIOS name cache and loads the #PRE entries found in the Lmhosts file into the NetBIOS name cache. Use this command to purge the name cache if you suspect that it contains incorrect information.

Nbtstat �RR Forces the computer to reregister its NetBIOS names with a WINS server. Use this command if the computer records in WINS do not exist or are incorrect.

You can also use Nbtstat to display the NetBIOS names registered by remote computers, or to display NetBIOS sessions. For complete information on the Nbtstat command-line options, open a command prompt and type Nbtstat /?.

Troubleshooting NetBIOS name resolution

Note


Practice: Configuring NetBIOS Name Resolution


In this practice, you will configure NetBIOS name resolution by using the Lmhosts file.


! Configure NetBIOS name resolution by using the Lmhosts file

1. If necessary, log on to DEN-DC1 as Contoso\Administrator with a password of Pa$$w0rd.

2. Click Start, point to All Programs, point to Accessories, and then click Command Prompt.

3. At the command prompt, type nbtstat -c and then press ENTER. Record any entries that appear in your cache: Answers will vary ____________________________________________________________

4. On DEN-DC1, browse to c:\windows\system32\drivers\etc. Right-click the Lmhosts.sam file and then click Open. When prompted, choose Notepad and then click OK.

5. At the end of the file, add the following entry: 10.10.0.10 Testserver2 #PRE

6. On the File menu, click Exit. When prompted to save the file, click Yes. 7. Rename Lmhosts.sam to Lmhosts. 8. At the command prompt, type nbtstat -R and then press ENTER.

Objective

Instructions

Practice


9. At the command prompt, type nbtstat -c and then press ENTER. Record any entries that appear in your cache: Answers will vary, but should now include an entry for Testserver2. ____________________________________________________________


! Prepare for the next lab

1. Shut down the DEN-SRV1 virtual machine without saving changes. 2. Start the DEN-CL1 virtual machine.


Lab: Resolving Names


In this lab, you will troubleshoot name resolution.

Ensure that the following virtual machines are running:

! DEN-DC1 ! DEN-CL1

Objectives

Instructions

Estimated time to complete this lab: 15 minutes


Exercise 1 Troubleshooting Name Resolution In this exercise, you will troubleshoot name resolution problems.

Instructions Ensure that the DEN-DC1 and DEN-CL1 virtual machines are started.

Scenario A computer that was used by one of the developers in your company is needed for a new employee. After receiving the computer, the new user reports that logging on to the network takes a very long time. Upon further investigation, you notice that the computer is unable to connect to several servers on the network by using their host name or NetBIOS name. You suspect that the developer may have changed the name resolution configuration on the computer for testing purposes. You need to configure the computer so that it can connect to the servers.

Tasks Specific instructions

1. Run names.bat on DEN-CL1.

a. Log on to DEN-CL1 as Contoso\Administrator, with a password of Pa$$w0rd.

b. Run D:\2277\Labs\Mod03\names.bat.

c. Log off of DEN-CL1.

2. Log on as Contoso\user1 and then attempt to connect to DEN-DC1.

a. Log on to DEN-CL1 as Contoso\User1, with a password of Pa$$w0rd. Note that it will take some time for the logon to complete.

b. Ping DEN-DC1. What is the result? __________________

c. Use the ipconfig command to display your resolver cache. What IP address is listed for DEN-DC1.contoso.msft? __________________

d. Use the net view command to connect to DEN-DC1. What is the result? __________________

e. Use the nbtstat command to view your NetBIOS name cache. What is the IP address listed for DEN-DC1? __________________

f. Why are you unable to connect to DEN-DC1? __________________

g. Log off of DEN-CL1.

3. Solve the host name resolution problem.

a. Log on to DEN-CL1 as Contoso\Administrator, with a password of Pa$$w0rd.

b. Remove all entries for DEN-DC1.contoso.msft from the Hosts file.

c. Ping DEN-DC1. What is the result? __________________

d. Use the ipconfig command to display your resolver cache. What IP address is listed for DEN-DC1.contoso.msft? __________________


(continued)

Tasks Specific instructions

4. Solve the NetBIOS name resolution problem.

a. Remove all entries for DEN-DC1 from the Lmhosts file.

b. Use the nbtstat command to purge the NetBIOS name cache.

c. Use the net view command to connect to DEN-DC1. What is the result? __________________

d. Use the nbtstat command to view your NetBIOS name cache.

e. What is the IP address listed for DEN-DC1? __________________

5. Complete the lab exercise. a. Close all programs and shut down all computers. Do not save changes.

b. To prepare for the next module, start the DEN-DC1 and DEN-SRV2 virtual machines.

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