Now that you've learned about DNS naming conventions, let's look at five basic concepts related to DNS. Each will be explored in more detail later in this chapter, but this introduction will give you an initial understanding of DNS concepts and terminology.There are five areas that we'll discuss: DNS servers, DNS resolvers, resource records, zones, and zone files.
The DNS system relies on a distributed database for efficient name resolution. These databases reside on DNS servers that manage the database. Computers that act as DNS servers run a program that manages the database structure and the information in it.This information is used to provide responses to client requests for name resolution. A DNS server can either respond to the request directly or provide a pointer to another DNS server that can help resolve the query. It can also respond that it does not know or that the information does not exist. A Windows Server 2003-based computer can be configured to run DNS as a server service.
Each DNS server is assigned a portion of the namespace over which it presides. The DNS server responsible for a contiguous portion of the namespace is said to be authoritative for that contiguous portion. Authority for a zone can be delegated to another server. Administrators often delegate authority for subdomains to other DNS servers.
DNS resolvers are programs that use DNS queries to request information from DNS servers. A resolver usually is built into a utility program or can be made accessible via library functions and can communicate with a remote DNS server or the DNS server running locally. A resolver can be run on any computer, including on a computer acting in the role of DNS server.
Resource records are sets of information used to resolve name resolution queries. A DNS server contains the resource records it needs to respond to name resolution queries for the namespace for which it is authoritative.
A zone is a contiguous portion of the domain name space for which a DNS server is authoritative. A zone is not a domain. A domain is a branch of the namespace; a zone is a portion of a namespace that can contain multiple domains.
Zone files are files that contain resource records for the zone for which the DNS server is authoritative. Typically, zone files are text files. In Windows Server 2003, they can also be stored in the Active Directory database. This implementation is discussed later in this chapter.
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