o Your registrar puts your DNS information into the global DNS database IT 263

O your registrar puts your dns information into the

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oYour registrar puts your DNS information into the global DNS database.IT 26314
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IT 263 & TDC 405 ‐ Autumn 201831 Oct 2018Dr. Oteafy © 20188The hierarchy in DNSRoot DNS servers13 of them in the world (each with 10’s of replicas)RootTop Level Domain serversHandling country specific (.ca) or organizational (.org. .com etc)TLDAuthoritative DNS serversUsually at organization level, or leased from a service providerAuthoritativeApplication Layer2-15DNS ServersRoot DNS Serversstore address of each DomainServer for a particular top‐level domain (i.e. “.edu”)Domain DNS Serversstore names and IP addressesforHosts/Devices in that Domain (depaul.edu)Other SubDomain Servers below them (cdm.depaul.edu)The range of names that each server storesinformation for is called itszone.
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IT 263 & TDC 405 ‐ Autumn 201831 Oct 2018Dr. Oteafy © 20189Zones and BackupsOne DNS server holds the authoritative DNS databaseof information for each zone.This server is the primary server for that zone.All changes to the DNS domain zone database must be madeat the primary serverAdditional secondary servers keep read‐only copies ofthe DNS zone database for backup and performancepurposes.Figure 16-6 Zone and domainsFigure 16-5 Hierarchy of name servers
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IT 263 & TDC 405 ‐ Autumn 201831 Oct 2018Dr. Oteafy © 201810Domain Name SystemSome Record Types kept in DNS databases:Address record (A) – stores IPv4 address corresponding to ahost nameQuad‐A record (AAAA) – stores IPv6 address corresponding toa host nameName Server record (NS) – stores the IP address for a DNSname server that handles a particular subdomainMail Exchange record (MX) – stores IP address for the e‐mailserver that handles mail for a particular domain.Carried out in 2 general waysDNS resolution
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IT 263 & TDC 405 ‐ Autumn 201831 Oct 2018Dr. Oteafy © 201811Application Layer2-21requesting hostcis.depaul.eduoteafy.cs.depaul.eduroot DNS serverlocal DNS serverdns.depaul.edu123456authoritative DNS serverdns.cs.depaul.edu78TLD DNS serverDNS nameresolution examplehost at cis.poly.eduwants IP address foroteafy.cs.depaul.eduiteratedquery:contacted server replies with name of server to contactI dont know this name, but ask this serverApplication Layer2-224563recursive query:puts burden of name resolution on contacted name serverheavy load at upper levels of hierarchy?requesting hostcis.poly.eduoteafy.cs.depaul.eduroot DNS serverlocal DNS serverdns.poly.edu127authoritative DNS serverdns.cs.depaul.edu8DNS name resolution exampleTLD DNS server
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IT 263 & TDC 405 ‐ Autumn 201831 Oct 2018Dr. Oteafy © 201812Can we afford to do this every timefor every hostname?
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