DNS: (Domain Name Server)
The DNS (Domain Name System, Domain Name Server, Domain Name Space) is a distributed database that use to map between IP addresses and hostnames.
No single site on the internet cotains all the information. Instead it is distributed amoung a number of sites. Each site maintains its own database and provides a server program that allows other systems (clients) on the internet to query.
Access to the DNS by an application is via a resolver. The resolver contacts one or more name servers to provide mapping.
The DNS name space is hierarchical, with an unnamed root branching to a number of standard top level domains. These top level domains can be further divided into secondlevel domains.
| identification | flags |
| number of questions | number of answers RRs |
| number of authority RRs | number of additional RRs |
| questions | |
| answers (variable number of resource records) |
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| authority (variable number of resource records) |
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| additional information (variable number of resource records) |
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