oYour registrar puts your DNS information into the global DNS database.IT 26314
IT 263 & TDC 405 ‐ Autumn 201831 Oct 2018Dr. Oteafy © 20188The hierarchy in DNS•Root DNS servers•13 of them in the world (each with 10’s of replicas)Root•Top Level Domain servers•Handling country specific (.ca) or organizational (.org. .com etc)TLD•Authoritative DNS servers•Usually at organization level, or leased from a service providerAuthoritativeApplication Layer2-15DNS Servers•Root DNS Serversstore address of each DomainServer for a particular top‐level domain (i.e. “.edu”)•Domain DNS Serversstore names and IP addressesfor–Hosts/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.
IT 263 & TDC 405 ‐ Autumn 201831 Oct 2018Dr. Oteafy © 20189Zones and Backups•One 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 server•Additional 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
IT 263 & TDC 405 ‐ Autumn 201831 Oct 2018Dr. Oteafy © 201810Domain Name System•Some Record Types kept in DNS databases:–Address record (A) – stores IPv4 address corresponding to ahost name–Quad‐A record (AAAA) – stores IPv6 address corresponding toa host name–Name Server record (NS) – stores the IP address for a DNSname server that handles a particular subdomain–Mail Exchange record (MX) – stores IP address for the e‐mailserver that handles mail for a particular domain.Carried out in 2 general waysDNS resolution
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 example•host at cis.poly.eduwants IP address foroteafy.cs.depaul.eduiteratedquery:contacted server replies with name of server to contact“I don’t know this name, but ask this server”Application 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
IT 263 & TDC 405 ‐ Autumn 201831 Oct 2018Dr. Oteafy © 201812Can we afford to do this every timefor every hostname?
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