chapter overview - wordpress.com · 2017-07-10 · 6 root domain the root domain is at the top of...
TRANSCRIPT
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Chapter Overview
� Understanding DNS
� Creating Zones
� Managing Resource Records
� Troubleshooting DNS
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Understanding DNS
� Domain Name System (DNS) is a name resolution mechanism that Transmission Control Protocol/Internet Protocol (TCP/IP) computers use to resolve host names and domain names into Internet Protocol (IP) addresses.
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Introduction to DNS
� DNS name resolution is different from Windows Internet Name Service (WINS).� WINS resolves Network Basic Input/Output
System (NetBIOS) names used on Microsoft Windows networks into IP addresses.
� DNS resolves host names used on all types of TCP/IP networks into IP addresses.
� Host names are user friendly, remain more constant than IP addresses, and let users connect to local servers by using the same naming convention that is used on the Internet.
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Domain Namespace
� The domain namespace is the naming scheme that provides the hierarchical structure for the DNS database.
� The domain is the basic unit of the DNS namespace.
� A domain's name identifies its position in the DNS hierarchy.
� As you add domains to the hierarchy, the name of the parent domain is appended to its child domain (called a subdomain).
� The domain namespace consists of a root domain, top-level domains, second-level domains, and host names.
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The Hierarchical Structure of the DNS Namespace
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Root Domain
� The root domain is at the top of the DNS hierarchy.
� It is represented as a period (.).
� Although it is rarely written as such, every fully qualified domain name (FQDN) should end with a period, representing the root domain.
� For example: sales.microsoft.com.
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Top-Level Domains
� The seven original top-level domains and the resources they represent are� com Commercial organizations
� edu Educational institutions in North America
� gov United States government institutions
� int Organizations established by international treaty
� mil United States military organizations
� net Networking organizations
� org Noncommercial organizations
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Second-Level Domains
� Second-level domain names must be registered with an Internet registrar, such as Network Solutions, Inc.
� There are millions of second-level domains in use by individuals and organizations.
� A second-level domain can contain both hosts and subdomains.
� Once you register a second-level domain name, you can create as many subdomains and hosts as you want in that domain.
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Host Names
� A host is a specific computer or other TCP/IP device on the Internet or a private network.
� A host name is the leftmost portion of an FQDN, which describes the exact position of a host within the domain hierarchy.
� For example, Computer1.sales.microsoft.com. is an FQDN, and Computer1 is the host name.
� DNS resolves an FQDN to its associated IP address.
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Domain Naming Guidelines
� When you create subdomains and hosts within your own second-level domain, consider these guidelines:
� Limit the number of domain levels.
� Use unique names.
� Use simple names.
� Avoid lengthy domain names.
� Use standard DNS characters.
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Zones
� Represent discrete portions of the namespace
� Provide a way to partition the domain namespace into manageable sections
� Must encompass a contiguous area of the domain namespace
� Typically include a domain and one or more of its subdomains
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Domain Namespace Divided Into Zones
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Name-to-IP-Address Mappings
� The name-to-IP-address mappings for a zone are stored in the zone database file.
� Each zone� Is anchored to a specific domain
� Contains all of the name-to-IP-address mappings for that domain, and for all subdomains in that zone
� If a new zone is created for a subdomain, all name-to-IP-address mappings for the subdomain are contained in the new zone, not in the zone that contains the parent domain.
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Name Servers
� A DNS name server stores the zone database file.
� A name server can store data for one zone or multiple zones.
� There must be at least one name server for a zone, although a zone can have multiple servers.� One of these servers contains the master zone
database file, also called the primary zone database file.
� Any other servers associated with the zone contain a secondary zone database file.
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Advantages of Multiple Name Servers
� There are several advantages of using multiple name servers for a zone:
� Performing zone transfers
� Providing redundancy and fault tolerance
� Improving access speed for remote locations
� Reducing the load on the server containing the primary zone database file
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Overview of the Name Resolution Process
� Name resolution converts host names or domain names to IP addresses.
� When you try to connect to a Web site, your Web browser contacts a DNS server to resolve the name of the Web site you entered to its associated IP address.
� The mapping of names to IP addresses is stored in the DNS distributed database.� The database is said to be distributed because its
information is stored in zones located on DNS name servers all over the Internet.
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Overview of the Name Resolution Process (Cont.)
� DNS name servers resolve forward and reverse lookup queries.� A forward lookup query resolves a name to an IP
address.
� A reverse lookup query resolves an IP address to a name.
� A name server can resolve a query only for names in a zone for which it has authority.
� If a name server cannot resolve a query, it passes the query to other name servers that can resolve the query.
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Forward Lookup Query
� The DNS service uses a client/server model for name resolution.
� To resolve a forward lookup query, a DNS client passes a query to a local name server.
� The local name server either resolves the query itself or transmits its own query to another name server for resolution.
� The local name server sends the IP address to the client, completing the process.
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Resolving a Forward Lookup Query
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Name Server Caching
� As a name server receives queries, it caches the query results.
� The query results are cached for the time specified in the Time to Live (TTL), which is specified by the zone that provided the query results.
� When the TTL expires, the name server deletes the query results from its cache.
� By caching query results, the name server can quickly resolve other queries to the same portion of the domain namespace.
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In-addr.arpa Domain
� Follows the same hierarchical naming scheme as the rest of the domain namespace.
� Based on IP addresses, not domain names.
� Subdomains are named after the numbers in the dotted-decimal representation of IP addresses.
� Order of the IP address octets is reversed.
� Companies administer subdomains of the in-addr.arpa domain based on their assigned IP addresses and subnet mask.
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An in-addr.arpa Domain ExampleIP Address 169.254.16.200
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Reverse Lookup Query
� A reverse lookup query maps an IP address to a name.
� Because the DNS distributed database is indexed by name and not by IP address, a special domain called in-addr.arpa was created.
� The in-addr.arpa domain follows the same naming scheme as the rest of the domain namespace, except that it is based on IP addresses, not domain names.
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Installing the DNS Service
� There are three ways to install the DNS Server service on a computer running Microsoft Windows 2000 Server:� Select it during operating system installation.
� Use Add/Remove Programs.
� Allow the Active Directory Installation Wizard to install and configure it.
� You should manually configure a DNS server with a static IP address, not one assigned by a Dynamic Host Configuration Protocol (DHCP) server.
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The Windows Components Page in the Windows Component Wizard
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The DNS Server Service Installation Process
� After installing the DNS Server service, you should configure the DNS server to use itself as its DNS server.
� The DNS Server service installation process does the following:� Installs the DNS console, which you can use to
manage DNS servers on your network
� Adds the following key to the registry: HKEY_LOCAL_MACHINE\System \CurrentControlSet\Services\DNS
� Creates the \systemroot\System32\DNS folder, which contains the DNS database files
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Lesson Summary
� DNS name resolution is the process of resolving host and domain names to IP addresses.
� The DNS namespace consists of multiple levels of domains, each of which can contain subdomains and hosts.
� A DNS name server contains one or more zones, each of which is a segment of the DNS namespace consisting of one or more domains.
� DNS servers perform two types of name resolutions: forward lookup queries and reverse lookup queries.
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Creating Zones
� DNS servers let you divide the DNS namespace into zones that store name information about one or more DNS domains.
� The zone becomes the authoritative source for information about each DNS domain included in it.
� You create and configure zones by using the DNS.
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Zone Planning
� When you install a DNS server for servicing a domain, you must create at least one zone.
� You can do either of the following:� Create one zone that contains the entire area of
the DNS namespace for which you are the authority
� Divide your domain into subdomains and place them in different zones
� Reasons for dividing into zones include administrative delegation, performance enhancement, fault tolerance, and namespace expansion.
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Creating a Zone
� Use the DNS console to create zones and manage the DNS servers on your network.
� The DNS console is installed during DNS installation.
� To access the console, click Start, point to Programs, point to Administrative Tools, and then click DNS.
� To run the DNS console on a computer running Windows 2000 computer that is not running the DNS Server service, you can install the Adminpak package.
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Creating a Zone (Cont.)
� When you create a zone, you must select a zone type.
Zone Type Description
Active Directory–integrated
The master copy of a new zone
The zone uses the Active Directory database to store and replicate the zone files.
Standard primary The master copy of a new zone stored in a standard text file
You administer and maintain this zone on the computer where it was created.
Standard secondary A replica of an existing zone
It is read-only and is stored in a standard text file.
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The Master DNS Servers Page in the New Zone Wizard
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The Reverse Lookup Zone Page in the New Zone Wizard
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Creating Active Directory–Integrated Zones
� Strongly recommended for networks deploying DNS to support the Active Directory service
� Provide these benefits:� Multiple-master update and enhanced security are
based on the capabilities of Active Directory.
� Zones are replicated and synchronized to new domain controllers automatically whenever a new zone is added.
� Planning and administration are simplified for both DNS and Active Directory.
� Directory replication is faster and more efficient than standard DNS replication.
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Delegating Zones
� A zone starts as the storage database for a single DNS domain name.
� If you add a subdomain below the domain you used to create the zone, you can configure it to be
� Managed and included in the original zone
� Delegated to another zone created to support the subdomain
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Delegating a New Subdomain to a New Zone
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Delegating a Zone
� When you delegate a zone, you are creating a Name Server (NS) resource record in the DNS database that points to the authoritative DNS server for the delegated zone.
� This record transfers authority and provides correct referrals to other DNS servers and clients.
� Use the DNS console to create a zone delegation.
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The Name Servers Page in the New Delegation Wizard
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The New Resource Record Dialog Box
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Configuring Dynamic DNS
� The DNS Server service includes a dynamic update feature called Dynamic DNS (DDNS).
� With DDNS, name servers and clients on a network automatically update the zone database files.
� You can configure a list of authorized servers to initiate dynamic updates, including secondary name servers, domain controllers, DHCP servers, WINS servers, and so on.
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Configuring Dynamic DNS (Cont.)
� DDNS interacts with the DHCP Server service to maintain synchronized name-to-IP-address mappings for network hosts.
� DHCP clients add their own Host (A) resource records to the zone.
� The DHCP Server service adds the Pointer (PTR) resource records to the zone.
� You use the DNS console to configure a zone for DDNS.
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Lesson Summary
� DNS servers let you divide the DNS namespace into zones that store name information about one or more DNS domains.
� DNS servers can have forward lookup and reverse lookup zones.
� You can create three types of zones: Active Directory–integrated zones, standard primary zones, and standard secondary zones.
� When a new subdomain is added, it can be delegated to a new zone created to support the subdomain.
� DDNS enables computers on the network to automatically update their resource records.
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Managing Resource Records
� The information in a DNS zone database file is stored in units called resource records.
� Resource records associate DNS domain names to related data, such as an IP address, for a particular resource.
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Understanding Resource Record Types
� There are many different types of resource records:
Type Function
Start of Authority (SOA) Identifies which name server is the authoritative source for data within the domain
Name Server (NS) Lists the name servers assigned to a particular domain
Host (A) Lists the host name-to-IP address mappings for a forward lookup zone
Alias (CNAME) Creates an alias, or alternate name, for the specified host name
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Understanding Resource Record Types (Cont.)
Type Function
Host Information (HINFO)
Identifies the CPU and operating system used by the host
Mail Exchanger (MX) Identifies which mail server to contact for a specified domain
Pointer (PTR) Points to another part of the domain namespace
In a reverse lookup zone, a PTR record contains IP-address-to-name mappings.
Service (SRV) Identifies which servers host a particular service
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Viewing Resource Records
� To view the information in a resource record:
1. Open the DNS console. 2. In the console tree, click the zone that contains
the resource record you want to view.3. In the details pane, right-click the record you
want to view, and then click Properties. 4. View the properties of the resource record, and
then click OK.
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The Properties Dialog Box for a Host (A) Record
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The Properties Dialog Box for a Start of Authority (SOA) Record
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Creating Resource Records
� To use the DNS console to create a new resource record:
1. Right-click the zone where you want the record to be located, and then select the appropriate command from the menu:
2. Enter information in the New Resource Record dialog box, and then click OK.
� New Host
� New Alias
� New Mail Exchanger
� New Domain
� New Delegation
� Other New Records
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The Resource Record Type Dialog Box
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The New Resource Record Dialog Box for a Host (A) Record
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Lesson Summary
� A DNS zone database file can contain many different types of resource records.
� A Start of Authority (SOA) record identifies the authoritative name server for the domain.
� An Alias (CNAME) record creates an alternate name for a host.
� Host (A) records contain basic name-to-IP-address mappings.
� Pointer (PTR) records contain IP-address-to-name mappings.
� Use the DNS console to view existing resource records and create new resource records.
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Troubleshooting DNS
� System administrators should understand
� The monitoring options available for DNS servers
� The problems that might occur in using DNS with Active Directory service and some possible solutions to these problems
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Monitoring DNS Servers
� Windows 2000 Server includes three options for monitoring DNS servers:
� Submitting queries to the server
� Default logging of DNS server event messages to the DNS server log
� Optional debug options for trace logging to a text file on the DNS server computer
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Querying the DNS Server
� To use the DNS console to monitor the DNS Server service:1. Select the name server, click the Action menu,
and then select Properties. 2. In the Properties dialog box, click the Monitoring
tab.
� You can test the server by performing two types of queries:� Simple query: a local test that uses the DNS client
on this computer to query the name server
� Recursive query: a more complex test that tests the name server by forwarding a query to another name server
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DNS Server Event Logging
� You can use Event Viewer to view the DNS server log.
� The DNS server log contains basic events logged by the DNS Server service, such as when the service starts and stops.
� You can also use Event Viewer to view and monitor client-related DNS events.
� The DNS client service generates these events, which appear in the System log on computers running Microsoft Windows 2000.
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Debug Options
� You can use the DNS console to set additional logging options to create a temporary trace log as a text-based file of DNS server activity for debugging purposes.
� To configure debug logging options:1. Right-click a DNS server in the DNS console, and
then select Properties.
2. Click the Logging tab, and then select the check boxes next to the options you want.
� By default, all debug logging options are disabled.
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The Logging Tab in a DNS Server’s Properties Dialog Box
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DNS Troubleshooting Scenarios
� Problem: A zone transfer may fail to occur.
� Possible causes:� The DNS Server service is stopped or the zone is
paused.
� The DNS servers used during a transfer may have network connectivity or interoperability problems.
� The SOA serial number may be the same at both the source and destination servers.
� The zone may have resource records or other data that the DNS server cannot interpret.
� The authoritative zone data might be incorrect.
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DNS Troubleshooting Scenarios (Cont.)
� Problem: A zone delegation does not function properly.
� Solution: The most likely cause of the problem is an incorrectly configured zone delegation.
� Review how zone delegations are used and revise zone configurations as needed.
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DNS Troubleshooting Scenarios (Cont.)� Problem: A client is not performing dynamic
updates.
� Possible causes:� The client, or its DHCP server, may not support DDNS.
� The client may not have been able to register and update with the DNS server due to incomplete DNS configuration.
� The client may have attempted to update its information with the DNS server but failed because of a problem with the server.
� The DNS server may not support dynamic updates.
� The DNS server may support dynamic updates, but may not be configured to accept them.
� The zone database may not be available.
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Lesson Summary� The Monitoring tab in a DNS server's Properties
dialog box lets you send simple and recursive queries to the server.
� Event Viewer contains a DNS server log on computers running Windows 2000 Server and the DNS Server.
� The Logging tab in a DNS server's Properties dialog box enables you to select specific server activities to monitor in a log file.
� Zone transfers can fail for many reasons, including network failures and unsupported data stored in the zone database.
� Dynamic updates often fail because not all of the computers involved support DNS.