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Domain Name System (DNS namespace (Hierarchical, starts with the root…
Domain Name System
DNS namespace
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TLDs then have sub-domains, such as qa, google
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Hostnames are added to a domain name to create Fully Qualified Domain Names (FQDNs) i.e. ns0.zen.co.uk
Domain names consist of individual labels separated by dots, for example: mydomain.microsoft.com.
Fully Qualified Domain Name (FQDN) uniquely identifies the hosts position within the DNS hierarchical tree by specifying a list of names separated by dots in the path from the referenced host to the root.
Query Order
1/ Is server authoritative? If yes, send answer
2/ Is the answer in the cache, if so send answer
3/. Check if it has a forwarder configured. If yes - send query to forwarder, cache answer, and response to client
4/ Send Iterative query to root Servers - work through referrals until it reaches the authoriative server. Cache answer and send to client
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Components
Server
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Responds to client requests, and provides mapping information
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Resource Records
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Name, record type, Record data, TTL
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CNAME canonical name, alias
PTR - reverse lookup, IP to Name
Query types
Recursive
the DNS server, who received your query will do all the job of fetching the answer, and giving it back to you
Iterative
iterative query, the name server, will not go and fetch the complete answer for your query, but will give back a referral to other DNS server's, which might have the answer
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Berkeley Internet Name Domain (BIND) - one of the first implementation, and still remains popular DNS server