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DREXEL ECES 490 - topic21

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PowerPoint PresentationThe Domain Name System (DNS)Slide 3Slide 4Slide 5The Domain Name SystemSlide 7Slide 8Slide 9DNS QueriesSlide 11Slide 12Slide 13DNS Resource RecordsCopyright 2002, S.D. Personick. All Rights Reserved. 1Telecommunications Networking II Topic 21The Domain Name System (DNS)Ref: Tanenbaum 622-630Dr. Stewart D. PersonickDrexel UniversityCopyright 2002, S.D. Personick. All Rights Reserved. 2The Domain Name System (DNS)•The principal purpose of the Domain Dame System (DNS) is to allow Internet hosts, and other entities that have IP addresses, to refer to each other by “names” that are easier to remember than 32-bit IP addresses•The concept is very similar to telephone numbers like 1-888-ProfStuCopyright 2002, S.D. Personick. All Rights Reserved. 3The Domain Name System (DNS)•The Domain Name System is based on a hierarchical naming schemeRootgov mil edu com org netus (etc.)Copyright 2002, S.D. Personick. All Rights Reserved. 4The Domain Name System (DNS)Examples:[email protected]@[email protected]@[email protected]@[email protected] 2002, S.D. Personick. All Rights Reserved. 5The Domain Name System (DNS)Domain names are [email protected] = [email protected]….some Web page names, e.g., WWW.Drexel.edu/… have case-sensitive fields after the “/” that follows the Top-Level domain name (e.g., .edu, .com, .org, .gov, ...)Copyright 2002, S.D. Personick. All Rights Reserved. 6The Domain Name System•Top-Level domains are either “generic” : .com, .edu, .gov, .mil, .net, .orgor “geographic”: .us, .jp, .it, ….•The original domain naming structure is being modified in order to introduce competition into the process of assigning domain namesCopyright 2002, S.D. Personick. All Rights Reserved. 7•Domains are managed by assigned entities (Registries + Registrars)•.org is managed by Network Solutions® (a subsidiary of Verisign®): historically, under a contract from the U.S. Government. If you want to establish a new .org domain name (example: stampcollectors.org), you ask Network Solutions to assign this name to you (if available). The Domain Name SystemCopyright 2002, S.D. Personick. All Rights Reserved. 8•.gov and .mil are managed by an entities under contract with the U.S. Government•.jp is managed by an an entity appointed by the Japanese government•The .com “Registry” is currently managed by Network Solutions Inc, but there are now multiple “Registrars”•New generic Top-Level Domains have been established by ICANN (e.g., .biz, .info, .pro, .aero, .name, .coop, .museum)The Domain Name SystemCopyright 2002, S.D. Personick. All Rights Reserved. 9The Domain Name System•The US Postal Service has suggested that it assign “.us” Internet names to everyone in the U.S., and that it administer the .us domain•Note: Assignment of names is a very contentious and litigious processCopyright 2002, S.D. Personick. All Rights Reserved. 10 DNS Queries•The naming hierarchy allows for distributed administration of the assignment of domain names…and the tables that link domain names to IP addressses:-Network Solutions administers .edu-Drexel Univ administers drexel.edu-The Drexel ECE Department can administer ece.drexel.eduCopyright 2002, S.D. Personick. All Rights Reserved. 11•Each entity that administers a part of the domain name space must maintain a server at a known address (or more than one server) which can be queried to translate domain names into IP addresses. •Translations can be cached, but are typically not cached for long (at least not at the lower levels of the hierarchy) DNS QueriesCopyright 2002, S.D. Personick. All Rights Reserved. 12•If you need to translate a domain name into an IP address, you ask your (“local”) domain name server. If it doesn’t have the translation (authoritative or cached), it will send a DNS query to a higher level server and/or another server at its own level in the hierarchy DNS QueriesCopyright 2002, S.D. Personick. All Rights Reserved. 13DrexelDNSDARPA DNS.milDNSRootDNS.eduDNS123IP address of:[email protected] DNS QueriesCopyright 2002, S.D. Personick. All Rights Reserved. 14DNS Resource RecordsDomain_name Time_to_live Class Type Value See Tanenbuam p 625: Time_to_live = integer (seconds, e.g., 86400) Class= IN (Internet information) Example Type: A (IP address of a host) Value: 32-bit


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