The domain name system 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.
Where does this topic fit? • Internet concepts • Applications • Technology (communication) • Implications • Internet skills • Application development • Content creation • User skills
Internet hosts 188.8.131.52 www.csudh.edu
IP addresses and domain names 184.108.40.206 = www.microsoft.com 220.127.116.11 www.microsoft.com
Domain name servers do the conversion www.microsoft.com 18.104.22.168 DNS server 22.214.171.124 www.microsoft.com DNS server
www.microsoft.com 126.96.36.199 DNS server 188.8.131.52 www.microsoft.com DNS server http://www.zoneedit.com/lookup.html
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
How are these hosts related? • bpastudio.csudh.edu • www.ucla.edu • sws.csudh.edu • chemistry.stanford.edu
How are these hosts related? • som.csudh.edu • www.csudh.edu • sws.csudh.edu • chemistry.csudh.edu
A unique host som.csudh.edu
Some generic top-level domains • .edu, educational • .com, commercial • .gov, government • .org, non profit • .net, networking organizations
Some country code top level domains • .us, United States • .mx, Mexico • .cl, Chile • .uk, United Kingdom • .tv, Tuvalu
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/
Name servers are decentralized ? Root name server ? Edu name server CSUDH name server
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.
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 <your name>.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?
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/#