Lesson 5: Domain Name System

DNS is a distributed database used in TCP/IP networks to translate computer names (hostnames) to IP addresses. This lesson introduces you to DNS and name resolution. It alsodiscusses the skills necessary and provides information to install and configure the DNSservice.
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Lesson 5: Domain Name System fLesson 5: Domain Name SystemDNS is a distributed database used in TCP/IP networks to translate computer names (hostnames) to IP addresses. This lesson introduces you to DNS and name resolution. It alsodiscusses the skills necessary and provides information to install and configure the DNSservice.Introduction to DNSDNS is most commonly associated with the Internet. However, private networks useDNS extensively to resolve computer host names and to locate computers within theirlocal networks and the Internet. DNS name resolution is different than the nameresolution provided by WINS. WINS resolves NetBIOS names to IP addresses, whileDNS resolves IP host names to IP addresses. IP host names resolved using DNS or othermeans, provide the following benefits: IP host names are user-friendly, which means they are easier to remember than IP • addresses. IP host names remain more constant than IP addresses. An IP address for a server • can change, but the server name remains the same. IP host names allow users to connect to local servers by using the same naming • convention as the Internet.Domain NamespaceDomain namespace is the naming scheme that provides the hierarchical structure for theDNS database. Each node represents a partition of the DNS database. These nodes arereferred to as domains.The DNS database is indexed by name; therefore, each domain must have a name. Asyou add domains to the hierarchy, the name of the parent domain is appended to its childdomain (called a subdomain). Consequently, a domains name identifies its position in thehierarchy. For example, in Figure 9.10 the domain name sales.microsoft.com identifiesthe sales domain as a subdomain of the microsoft domain and microsoft as a subdomainof the com domain.Figure 9.10 Hierarchical structure of a domain namespaceAs Figure 9.10 illustrates, the hierarchical structure of the domain namespace consists ofa root domain, top-level domains, second-level domains, and host names.Root DomainThe root domain is at the top of the hierarchy and is represented as a period (.). TheInternet root domain is managed by several organizations, including Network Solutions,Inc.Top-Level DomainsTop-level domains are two-character or three-character name codes. Top-level domainsare categorized by organization type or geographic location. Thefollowing table providessome examples of top-level domain names. Top-level domain Descriptiongov Government organizationscom Commercial organizationsedu Educational institutionsorg Noncommercial organizationsau Country code of AustraliaTop-level domains can contain second-level domains and host names.Second-Level DomainsOrganizations such as Network Solutions, Inc. assign and register second-level domainsto individuals and organizations for the Internet. A second-level domain can contain bothhosts and subdomains. For example, microsoft.com can contain computers such asftp.microsoft.com and subdomains such as dev.microsoft.com. The subdomaindev.microsoft.com can contain hosts such as printerserver1.dev.microsoft.com.Host NamesHost names refer to specific computers on the Internet or a private network. For example,in Figure 9.10, Computer1 is a host name. A host name is the leftmost portion of a fullyqualified domain name (FQDN), which describes the exact position of a host within thedomain hierarchy. In Figure 9.10, Computer1.sales.microsoft.com. (including the endperiod, which represents the root domain) is an FQDN.DNS uses a hosts FQDN to resolve a name to an IP address.Domain Naming GuidelinesWhen you create a domain namespace, consider the following domain guidelines andstandard naming conventions: Limit the number of domain levels. Typically, DNS host entries should be three • or four levels down the DNS hierarchy and no more than five levels down the hierarchy. As the number of levels increases, so do the administrative tasks. Use unique names. Each subdomain must have a unique name within its parent • domain to ensure that the name is unique throughout the DNS namespace. Use simple names. Simple and precise domain names are easier for users to • remember and enable users to search intuitively and locate Web sites or other computers on the Internet or an intranet. Avoid lengthy domain names. Domain names can be up to 63 characters, • including the periods. The total length of an FQDN cannot exceed 255 characters. Case-sensitive naming is not supported. Use standard DNS ...