Transcript Pres 6 Domain Name System

DOMAIN NAME SYSTEM
Domain Name System
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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
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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
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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