1. Skills: none Concepts: domain, domain name, host, IP address, domain registrar This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License. The domain name system

2. Where does this topic fit? Internet concepts – Applications – Technology (communication) – Implications Internet skills – Application development – Content creation – User skills

3. Internet hosts 155.135.55.165 www.csudh.edu

4. IP addresses and domain names 65.55.12.249 www.microsoft.com 65.55.12.249 = www.microsoft.com

5. Domain name servers do the conversion www.microsoft.com 65.55.12.249 DNS server 65.55.12.249 www.microsoft.com DNS server

6. http://www.zoneedit.com/lookup.html www.microsoft.com 65.55.12.249 DNS server 65.55.12.249 www.microsoft.com DNS server

7. The parts of a domain name The particular host is called som The organization that owns the name it is csudh This host is at an educational organization som.csudh.edu

8. How are these hosts related? bpastudio.csudh.edu www.ucla.edu sws.csudh.edu chemistry.stanford.edu

9. How are these hosts related? som.csudh.edu www.csudh.edu sws.csudh.edu chemistry.csudh.edu

10. A unique host som.csudh.edu

11. Some generic top-level domains.edu, educational.com, commercial.gov, government.org, non profit.net, networking organizations

12. Some country code top level domains.us, United States.mx, Mexico.cl, Chile.uk, United Kingdom.tv, Tuvalu

13. Some TLDs use a four-level hierarchy http://www.google.co.uk/ http://www.unam.edu.mx/ http://www.ox.ac.uk/ http://www.google.com.mx/

14. rootcomorgneteduUCLAUSCCSUDHsommathwwwswslibrary…CSULB…tvus… The system is hierarchical

15. CSUDH name server Edu name server Root name server Name servers are decentralized ? ?

16. Summary We’ve seen that domains are groups of related computers. Domains have names. Individual hosts have unique, fully qualified domain names. The top level domains seldom change, but people are constantly registering new second-level domains. Domain name servers keep track of the correspondence between IP addresses and the corresponding domain names. Responsibility for maintain ing the lists of names and addresses is decentralized.

17. Self-study questions Are there more hosts in the.edu domain or the csudh.edu domain? Can two hosts have the same domain name? Can two hosts be in the same top level domain? Can two hosts be in the same second level domain? Is the.com domain name available for purchase? If so, how much would it cost? Why do you get an error message when you try to go to http://www.google.xom? http://wwww.google.com also returns an error message. Why?

18. Resources A DNS lookup web site (forward and backward): http://www.zoneedit.com/lookup.html For most generic TLDs there are many registrars and a competitive registration market place: http://www.icann.org/en/registrars/accredited-list.html The registrar for.edu is a professional society called Educause: http://net.educause.edu/edudomain/ List of organizations responsible for registrars in the country code domains: http://www.iana.org/domains/root/db/#