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[[Category: OPS335]][[Category:rchan]]
= What is DNS (Domain Name System)? =
* a hierarchical, distributed database
* for mapping Internet host names to IP addresses and vice versa
* provides mail routing information
= What are the components in the DNS? =
* DNS Clients
* resolver library
* DNS server
DNS clients (e.g. Web browser is one of those) look up information in the DNS by calling a resolver library, which sends queries to one or more name servers and interprets the response.
* Domains and Domain Names
* Zones
= DNS Servers =
== Authoritative Name Servers ==
A name server which contains the complete data for a zone.
* The primary master DNS server: maintains the master copy of the zone data
* Slave DNS servers: (aka secondary servers) load the zone contents from another server using a replication process known as zone transfer.
== Non-authoritative Name Servers ==
* Caching Name Server, or recursive name server
A name server which performs recursive lookups for local clients. Recursive name servers normally cache the results of the lookups they perform to improve performance.
* Forwarder
Some a caching name server may not perform the recursive lookup all by itself. It can forward some or all of the queries to another caching name server, commonly referred to as a forwarder.
= Root Zone and Root Name Server =
* ftp://ftp.rs.internic.net/domain/