domain name system. domain name system hostname resolution dns name lookup with dns domain name...
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DOMAIN NAME SYSTEM
Domain Name System
• Hostname Resolution
• DNS
• Name Lookup with DNS
• Domain Name Servers
• DNS Database
• Reverse Lookups
Hostname Resolution
• TCP/IP uses 32 bit address (dotted decimal)
• Hard for us - we use “ordinary” (canonical) names
• Host Name Resolution - application must find IP address corresponding to name
• Lookup routines provided by resolver library (gethostbyname & gethostbyaddr)
• Solutions:– Local file (/etc/hosts)
• maintenance problem
– Network Information System (NIS)• stores host file info in master database
• OK for small nets (maint & distribution)
– Network Information Center (NIC) HOSTS.TXT• pre-1984
• central site - maint & distribution problems
Domain Name System• Hierarchy of domains
– edu (Mostly US) educational institutions like universities, etc.
– com Commercial organizations, companies.
– org Non-commercial organizations.
– net Gateways and other administrative host on a network
– mil US military institutions
– gov US government institutions.
– Outside USA:• fr - france
• de - Germany
• au - Australia
Name Lookup with DNS
• Giant distributed database
• Name Servers provide info on a domain or set of domains
• Two (or more) name servers per zone (see whois)
Sample Lookup
• Your host needs address of slotnick.psycho.havid.edu• host queries names server at root domain• root name server (rns) - not in my domain - in .edu domain• rns contacts edu zone name server (zns) - list provided to rns• rns queries one of the edu zns • edu zns knows havid.edu runs a root of their own & points rns
to it • rns presents query for slotnik to havid.edu rns & IP address is
returned• info (Ipfor slotnick, havid.edu & .edu) cached for a TTL period
(just in case)
Domain Name Servers
• Authoritative (Master name servers)
• Primary/secondary
DNS Database
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