Vorlesung Kommunikationsnetze Domain Name System

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1 Picture Vorlesung Kommunikationsnetze Domain Name System Prof. Dr. H. P. Großmann mit B. Wiegel sowie A. Schmeiser und M. Rabel Sommersemester 2009 Institut für Organisation und Management von Informationssystemen

2 Page 2 Domain Name System (DNS) A distributed database used by TCP/IP applications translates between symbolic names and IP addresses provides mail routing information jedi.e-technik.uni-ulm.de student.uni-ulm.de smtp.uni-ulm.de pike.cs.ucla.edu

3 Page 3 Top Level Domains (TLD) root. com edu gov int mil generic (or organizational) domains net org... de us... country (or geographical) domains

4 Page 4 Generic Domains Domain Description aero arpa biz cat com coop edu gov info int jobs mil mobi services museum name net org pro travel air transport industry infrastructure domain business Catalan linguistic and cultural community commercial organizations cooperative associations educational institutions U.S. government information international treaty organizations human resource managers U.S. military consumers and providers of mobile products and museums individuals major network support centers other organizations credentialed professionals entities with primary area of activity is in the travel

5 Page 5 Generic Domains.AERO.ARPA.ASIA.BIZ.CAT.COM.COOP.EDU.GOV.INFO.INT.JOBS.MIL.MOBI.MUSEUMS.NAME.NET.ORG.PRO.TEL.TRAVEL air transport industry infrastructure domain restricted to the Pan-Asia and Asia Pacific community business Catalan linguistic and cultural community commercial organizations cooperative associations educational institutions U.S. government information international treaty organizations human resource managers U.S. military consumers and providers of mobile products and services museums individuals major network support centers other organizations credentialed professionals for businesses and individuals to publish their contact data entities with primary area of activity is in the travel industry Source:

6 Page 6 Country Code Domains Domain Country ar be cn cm de eg fr in mx tn us.. Argentina Belgium China Cameroon Germany Egypt France India Mexico Tunisia USA

7 Page 7 Domain Names Organizations apply for names within a top-level domain: uni-ulm.de unesco.org hp.com Organizations determine their DNS structure Flat namespace uni-ulm.de, gmd.de, mwk.de, siemens.de,... Convenient and short Hierarchical namespace u-tokyo.ac.jp, e-technik.uni-ulm.de, cs.ncsu.edu, siemens.co.uk,... Delegating authorities Each organization runs its DNS and maintains its information database

8 Page 8 Example of DNS Hierarchy top level domain de second level domains uni-ulm third level domains e-technik kiz medizin

9 Page 9 Name to Address Resolution A host wants the IP address of jedi.e-technik.uni-ulm.de: request to resolve jedi.e-technik.uni-ulm.de name server X host answer is

10 Page 10 What does a name server X do when it does not contain the requested information? name server X contacts other name servers Each name server knows about the higher level name servers The lowest level server knows the answer of the request (e.g. IP address)

11 Page 11 Hierarchy of Name Servers root name servers (currently are 13) a.root-servers.net... m.root-servers.net the authoritative name servers for root domain know names and IP addresses of each authoritative name server for all the top level domains authoritative name servers for a top level domain (e.g. de - 6 at the moment) know names and IP addresses of each authoritative name server for the second level domains authoritative name servers for a second level domain (e.g. uni-ulm.de - 4 at the moment)...

12 Page 12 Domain Name Resolution 1 2 request to resolve jedi.e-technik.uni-ulm.de request to resolve jedi.e-technik.uni-ulm.de name server X host answer: all IP addresses and names of NSs authoritative for the Top Level Domain de (e.g. a.nic.de) 3 answer: root name server (e.g. a.root-servers.net) request to resolve jedi.e-technik.uni-ulm.de name server 5 6 name server X caches all answers 7 answer: all IP addresses and names of NSs authoritative for the domain uni-ulm.de (e.g. dns1.uni-ulm.de) (e.g. a.nic.de) request to resolve jedi.e-technik.uni-ulm.de answer: and all IP addresses and names of NSs authoritative for the domain e-technik.uni-ulm.de (e.g. dns1.uni-ulm.de) name server (e.g. dns1.uni-ulm.de

13 Page 13 Resource Records Examples of types of entries in the DNS database Type Meaning A NS PTR MX SOA host address name server pointer record mail exchanger start of authority Description IP address for a given name NSs of a domain name for a given IP address receiver of a mail address the server supplies the zone s data

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