18-03-2011, 06:39 PM
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| M.Arsalan Qureshi | | Join Date: Oct 2008 Location: Garden Town, Multan Cantt
Posts: 616
Program / Discipline: BSTS Class Roll Number: 09-31 | |
Domain Name System Domain Name System * Domain Name System (DNS) is a client-server application that identifies each host on the Internet with a unique user-friendly name. * DNS organizes the name space in a hierarchical structure to decentralize the responsibilities involved in naming. * DNS can be pictured as an inverted hierarchial tree structure with one root node at the top and a maximum of 128 levels. * Each node in the tree has a domain name. * A domain is defined as any subtree of te domain name space. * The name space information is distributed among DNS servers. Each server has jurisdiction over its zone. * A root server's zone is the entire DNS tree. * A primary server creates, maintains, and updates information about its zone. * A secondary server gets its information from a primary server. * The domain name space in the Internet is divided into three sections: generic domains, country domains, and inverse domains. * There are seven traditional generic labels, each specifying an organization type. Recently some new labels have been added. * Each country domain specifies a country. * The inverse domain finds a domain name for a given IP address. This is called address-to-name resolution. * Name servers, computers that run the DNS server program, are organized in a hierarchy. * The DNS client, called a resolver, maps a name to an address or an address to a name. * In recursive resolution, the client may send its request to multiple servers before getting an answer. * In iterative resolution, the client may send its request to multiple servers before getting an answer. * A fully qualified doman name (FQDN) is a domain name consisting of labels beginning with the host and going back through each level to the root node. * A partially qualified domain name (PQDN) is a domain name that does not include all the levels between the host and the root node. * There are two types of DNS messages: queries and responses. * There are two types of DNS records: question records and resource records. * Dynamic DNS (DDNS) automatically updates the DNS master file. * DNS uses the services of UDP for messages of less than 512 bytes; otherwise, TCP is used.
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