【正文】 into play: If a DNS server does not know which server is configured with the address, it can request the server that is responsible for maintaining addresses of servers at each level in the hierarchy until it locates the authoritative server. For example, if the DNS server does not know which server is responsible for the server named , the DNS server can ask the server that is responsible for supplying the names of DNS servers in the . domain to provide the address of the server that is responsible for providing the addresses of DNS servers in the domain. The original DNS server can then query that server for the address of the puter named . DNS requires little ongoing maintenance for small businesses, which typically have one to four DNS servers. (Mediumsize anizations usually have 4 to 14 DNS servers.) DNS problems, however, can affect server availability for your entire work. Most DNS problems occur because DNS settings are configured incorrectly or obsolete records remain on the DNS servers. By following the procedures in this guide, you can avoid such problems when you deploy DNS in a simple work that is based on the Windows Server174。 2020 operating system. This guide explains how to install and configure a basic DNS implementation in a work that consists of a single, new Active Directory174。 Domain Services (AD DS) domain. The guide then addresses some advanced issues that mediumsize anizations may have to consider. Finally, it includes some basic DNS troubleshooting steps that you can take if you suspect that your environment has problems with DNS. In this guide 6 ?? Planning DNS ?? Installing and Configuring AD DS and DNS ?? Configuring Client Settings ?? Advanced DNS Configuration ?? Troubleshooting DNS Planning DNS Domain Name System (DNS) is the primary method for name resolution in Windows Server174。 2020 and for other versions of Microsoft174。 Windows174。 operating systems, such as Windows 2020, Windows XP, Windows Server 2020, and Windows Vista. DNS is a requirement for deploying the Active Directory Domain Services (AD DS) server role. Integrating DNS with AD DS makes it possible for DNS servers to take advantage of the security, performance, and faulttolerance capabilities of AD DS. Typically, you anize your DNS namespace (that is, the association of domains, subdomains, and hosts) in a way that supports your plan for using AD DS to anize the puters on your work. Understanding the DNS namespace The following illustration shows how the DNS namespace is anized. 7 A DNS name consists of two or more parts separated by periods, or dots (.). The last (rightmost) part of the name is called the toplevel domain (TLD). Other parts of the name are subdomains of the TLD or another subdomain. The names of the TLDs are either functional or geographical. Subdomains usually refer to the anization that owns the domain name. Functional TLDs suggest the purpose of the anization that has registered a subdomain in the TLD. The following table shows some of the most mon functional TLD names. Functional TLD Typically used by … . Commercial entities, such as corporations, to register DNS domain names .edu Educational institutions, such as colleges, and public and private schools .gov Government entities, such as federal, state, and local governments . Organizations that provide Inter services, such as Inter service providers (ISPs) 8 Functional TLD Typically used by … . Private, nonprofit anizations Geographical TLDs indicate the country or region where the anization that registered the domain is located. For example, an anization that wants to show that it is located in Canada registers its Inter domain name in the .ca TLD, and an anization that wants to show that it is located in Brazil registers its Inter domain name in the .br TLD. Most anizations that want to have an Inter presence for a Web site or that want to send and receive messages, for example, register an Inter domain name that is a subdomain of a TLD. Usually, they choose a subdomain name based on their anization39。s name, such as or . Most small anizations work with their Inter service provider (ISP) to register their domain name, although you can also register your domain name directly with a registrar that is listed at InterNIC ( Registering an Inter domain name reserves the name for the exclusive use of the anization and configures DNS servers on the Inter to provide the appropriate IP address when those servers are queried for that name. That is, it creates the equivalent of a telephone directory entry for the Inter domain name. But instead of providing a telephone number for the name, it provides the IP address that a puter requires to access the puters in the registered domain. The DNS namespace is not limited to only the publicly registered Inter domain names. Organizations that have works with their own DNS servers can create domains for their internal use. As the next section explains, these internal DNS namespaces can be—but are not required to be—subdomains of a public Inter domain name. Designing a DNS namespace You can design an external namespace that is visible to Inter users and puters. You can also design an internal namespace that is visible only to users and puters that are in your internal work. Organizations that require an Inter presence and an internal namespace must deploy both an internal and an external DNS namespace and manage each namespace separately. In this case, we remend that you make your internal domain a subdomain of your external domain. For example, an anization that has an external domain name of might use the internal domain name . Using an internal domain that is a subdomain of an external domain has the following advantages: ?? Requires you to register only one name with an Inter