Introduction to DNS

Basic DNS Concepts

This section provides brief definitions of additional DNS concepts, which are described in more detail in the following sections of this chapter.

DNS servers. Computers that run DNS server programs containing DNS database information about the DNS domain tree structure. DNS servers also attempt to resolve client queries. When queried, DNS servers can provide the requested information, provide a pointer to another server that can help resolve the query, or respond that it does not have the information or that the information does not exist.

DNS resolvers. Programs that use DNS queries to query for information from servers. Resolvers can communicate with either remote DNS servers or the DNS server program running on the local computer. Resolvers are usually built into utility programs or are accessible through library functions. A resolver can run on any computer, including a DNS server.

Resource records. Sets of information in the DNS database that can be used to process client queries. Each DNS server contains the resource records it needs to answer queries for the portion of the DNS namespace for which it is authoritative. (A DNS server is authoritative for a contiguous portion of the DNS namespace if it contains information about that portion of the namespace.)

Zones. Contiguous portions of the DNS namespace for which the server is authoritative. A server can be authoritative for one or more zones.

Zone files. Files that contain resource records for the zones for which the server is authoritative. In most DNS implementations, zones are implemented as text files.