Chapter Overview

1. Chapter Overview • Understanding DNS • Creating Zones • Managing Resource Records • Troubleshooting DNS

2. 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.

3. 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.

4. 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.

5. The Hierarchical Structure of the DNS Namespace

6. 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.

7. 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

8. 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.

9. 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.

10. 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.

11. 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

12. Domain Namespace Divided Into Zones

13. 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.

14. 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.

15. 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

16. 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.

17. 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.

18. 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.

19. Resolving a Forward Lookup Query

20. 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.

21. 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.

22. 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.

23. The Windows Components Page in the Windows Component Wizard

24. 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

25. 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.

26. 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.

27. 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.

28. 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.

29. Creating a Zone (Cont.) • When you create a zone, you must select a zone type.

30. The Master DNS Servers Page in the New Zone Wizard

31. The Reverse Lookup Zone Page in the New Zone Wizard

32. 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.

33. 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

34. Delegating a New Subdomain to a New Zone

35. 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.

36. The Name Servers Page in the New Delegation Wizard

37. The New Resource Record Dialog Box

38. 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.

39. 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.

40. 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.

41. Managing Resource Records • The information in a DNS zone database file is stored in units called resource records. • Resource recordsassociate DNS domain names to related data, such as an IP address, for a particular resource.

42. Understanding Resource Record Types • There are many different types of resource records:

43. Understanding Resource Record Types (Cont.)

44. 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.

45. The Properties Dialog Box for a Host (A) Record

46. The Properties Dialog Box for a Start of Authority (SOA) Record

47. 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 Domain • New Delegation • Other New Records • New Host • New Alias • New Mail Exchanger

48. The Resource Record Type Dialog Box

49. The New Resource Record Dialog Box for a Host (A) Record

50. 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.