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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  Name Systems and TCP/IP Name Registration and Name Resolution            9  TCP/IP Name Systems: Host Tables and Domain Name System (DNS)                 9  TCP/IP Domain Name System (DNS)                      9  DNS Overview, Functions and Characteristics

DNS Design Goals, Objectives and Assumptions 1 2 DNS Name Space, Architecture and Terminology

Name Resolution

DNS uses a powerful, distributed, client/server name resolution mechanism. This is probably the area where the most attention had to be put into the design of DNS, to ensure that it could scale to handle millions and eventually billions of name resolution requests each day.

The name resolution process is implemented using two basic software elements that play the role of client and server: name servers and name resolvers.

DNS name servers are special programs running on hardware servers that are the heart of DNS. Servers are maintained by organizations that have administrative control over part of the DNS name space, and contain resource records that describe names, addresses and other characteristics of those portions of the name space. As such, the servers themselves are arranged into a hierarchy analogous to that of the name space, though not identical in structure.

The main job of name servers is to receive requests for name resolution and either respond with the data requested from the database, or with the name of another name server that will lead to the requested information. Name servers are also responsible for data caching and other administrative tasks to ensure efficient operation of the system as a whole.

Name resolvers are the usual clients in the name resolution process. When a user makes reference to a name in a networking application, the name is passed to the resolver, which issues a request to a name server. Depending on the configuration, more than one request may be needed, and several different resolution processes may be combined to find the needed information. Resolvers too may employ caching or implement other features.

If this seems a lot like the “classic” description of a name system that I gave in the name system concepts section, that's not a coincidence; DNS is considered the name system against which most others are usually compared. If you understand these high-level descriptions, then you already know the basics of how DNS works. The next three sections delve into each of these three functional areas in more detail, and will help you really learn how DNS does its thing.

DNS Design Goals, Objectives and Assumptions 1 2 DNS Name Space, Architecture and Terminology