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DNS ("Domain Name System" (Hierarchical decentralized naming…
DNS
"Domain Name System"
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For computers, services, or other resources
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Defines a detailed specification of the data structures and data communication exchanges used in the DNS
Name space
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A DNS zone may consist of only one domain, or may consist of many domains and sub-domains
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Name syntax
Consists of one or more parts, technically called labels, that are conventionally concatenated, and delimited by dots
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History
The Stanford Research Institute maintained a text file named HOSTS.TXT that mapped host names to the numerical addresses of computers on the ARPANET
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To request a hostname and an address and add a computer to the master file, users contacted the SRI's Network Information Center
By the early 1980s, maintaining a single, centralized host table had become slow
In 1984, four UC Berkeley students, wrote the first Unix name server implementation for the Berkeley Internet Name Domain
It was widely distributed, especially on Unix systems
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Operation
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DNS resolvers
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Responsible for initiating and sequencing the queries that ultimately lead to a full resolution of the resource sought
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Record caching
Standard practice in implementing name resolution in applications is to reduce the load on the Domain Name System servers by caching results locally
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Function
DNS can be quickly updated, allowing a service's location on the network to change without affecting the end users
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Protocol transport
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DNS queries consist of a single UDP request from the client followed by a single UDP reply from the server
When the length of the answer exceeds 512 bytes and both client and server support EDNS, larger UDP packets are used. Otherwise, the query is sent again using the Transmission Control Protocol