Domain Name System - DNS

Domain Naming and Registration with DNS

Though IP addresses allow computers and routers to identify each other efficiently, humans prefer to work with names rather than numbers. The Domain Name System - DNS - supports the best of both worlds... (see below)

More of this Feature • IP Address Notation • IP Address Classes, Broadcast and Multicast • IP Loopback and Private Addresses, IPv6 Anycast • DNS - Domain Name System • IP Network Numbering • IP Subnetting • CIDR - Classless Internet Domain Routing Related Resources • IP Practice Test • TCP/IP Resources • Network Protocol Resources Elsewhere on the Web • ICANN ... . DNS allows nodes on the public Internet to be assigned both an IP address and a corresponding name, called a domain name. For DNS to work as designed, these names must be unique worldwide. Hence an entire "cottage industry" has emerged around the purchasing of domain names in the Internet name space. DNS Name Space DNS is a hierarchical system. DNS organizes all registered names in a tree structure. At the base or root of the tree are a group of top-level domains including familiar names like com, org, and edu and numerous country-level domains like fi (Finland), ca (Canada), and my (Malaysia). One generally cannot purchase names at this level. However, in a well-publicized and controversial event in 2000, the island nation of Tuvalu agreed to receive a large payment in return for rights to the root domain tv. Below this level are the second-level registered domains such as about.com. These are domains that organizations can purchase from any of numerous accredited registrars. For nodes in the com, org, and edu domains, the Internet Corporation for Assigned Names and Numbers (ICANN) oversees registrations. Below that, local domains like compnetworking.about.com are defined and administered by the overall domain owner. DNS supports additional tree levels as well. The period ('.') always separates each level of the hierarchy in DNS. DNS Root Level and Other Servers DNS is also a distributed system. The DNS database contains a list of registered domain names. It further contains a mapping or conversion between each name and one or more IP addresses. However, DNS requires a coordinated effort among many computers (servers); no one computer holds the entire DNS database. Each DNS server maintain just one piece of the overall hierarchy - one level of the tree and then only a subset or zone within that level. The top level of the DNS hierarchy, also called the root level, is maintained by a set of 13 servers called root name servers. These servers have gained some notoriety for their unique role on the Internet. Maintained by various independent agencies, the servers are uniquely named A, B, C and so on up to M. Ten of these servers reside in the United States, one in Japan, one in London, and one in Stockholm, Sweden. DNS Resolvers DNS works in a client/server fashion. DNS servers respond to requests from DNS clients called resolvers. ISPs and other organizations set up local DNS resolvers as well as servers. Most DNS servers also act as resolvers, routing requests up the tree to higher-level DNS servers, and also delegating requests to other servers. DNS servers eventually return the requested mapping (either address-to-name or name-to-address) to the resolver. DNS and DHCP DNS was not designed to work with dynamic addressing such as that supported by DHCP. DNS requires that fixed (static) addresses be maintained in the database. Web servers in particular require fixed IP addresses for this reason.