The domain name system (DNS) Skills: none IT concepts: domain, domain name, host, IP address, domain registrar This work is licensed under a Creative Commons Attribution-NoncommercialShare Alike 3.0 License. The domain name system (DNS) in context • Internet concepts – Applications – Technology (TCP/IP) – Implications for • Individuals • Organizations • Society • Internet skills – Application development – Content creation • Text • Images • Audio • Video Domain names We refer to computers on the Internet (Internet hosts), by names like: bpastudio.csudh.edu These are called domain names or, if you want to be really geeky, “fully qualified domain names.” The key point is that the name identifies a particular computer – no two hosts have the same domain name. The parts of a domain name bpastudio.csudh.edu The particular host is called bpastudio The organization that controls it is called csudh This host is at an educational organization A domain is a group of related hosts. How are these hosts related? • • • • bpastudio.csudh.edu www.ucla.edu sws.csudh.edu chemistry.stanford.edu They all belong to educational institutions. They are members of the edu top-level domain (TLD). How are these hosts related? • • • • bpastudio.csudh.edu www.csudh.edu sws.csudh.edu chemistry.csudh.edu They all belong to the same organization, CSUDH. They are members of the csudh.edu second-level domain. A unique host bpastudio.csudh.edu This is the domain name of a unique host. It is a member of the csudh.edu domain, but it is the only one with the name bpastudio. It is like a family – all the brothers and sisters have the same last name, but it would be confusing if two of them also had the same first name. There are a limited number of top-level domains (TLDs), including: • • • • • .edu, educational .com, commercial .gov, government .org, non profit .net, networking organizations These are called “generic” TLDs. There are also country code top-level domain names for every nation, like: • • • • • .us, United States .mx, Mexico .cl, Chile .uk, United Kingdom .tv, Tuvalu These are called “country code” top-level domains (ccTLDs). The organization or host do not necessarily have to be in the country to register the name. For example, .tv is popular everywhere. 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/ Registrars sell domain names • For most generic TLDs there are many registrars and a competitive registration market place: – http://www.icann.org/en/registrars/accreditedlist.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/# Regstering a domain – check for availability Larrypress.com was taken, but these are available and for sale Getting a name and IP address at CSUDH • A computer center staff person assigns them. • No two IP addresses or domain names can be the same. • The staff person updates the table of domain names and IP addresses stored on the CSUDH domain name server. Some hosts in the csudh.edu domain Domain name IP address sws.csudh.edu 188.8.131.52 ctl.csudh.edu 184.108.40.206 email.csudh.edu 220.127.116.11 ns1.csudh.edu 18.104.22.168 vaquero.csudh.edu 22.214.171.124 toro3.csudh.edu 126.96.36.199 music1.csudh.edu 188.8.131.52 home.muphiepsilon.org 184.108.40.206 library.csudh.edu 220.127.116.11 We are letting muphiepsilon.org use a computer on our campus. Some hosts in the csudh.edu domain Domain name IP address sws.csudh.edu 18.104.22.168 ctl.csudh.edu 22.214.171.124 email.csudh.edu 126.96.36.199 ns1.csudh.edu 188.8.131.52 vaquero.csudh.edu 184.108.40.206 toro3.csudh.edu 220.127.116.11 music1.csudh.edu 18.104.22.168 home.muphiepsilon.org 22.214.171.124 library.csudh.edu 126.96.36.199 Every domain has a domain name server (DNS). Our DNS is ns1.csudh.edu. It does the IP address lookups for TCP.. DNS search • If your DNS knows the IP address it returns it. • Otherwise it will contact another DNS to get the result. • Etc. until it is found or determined that it does not exist, in which case an error message is returned. Food for thought • Is the <your name>.com domain name available? • When you try to go to http://www.google.xom, you get an error message, but http://www.gooogle.com takes you to Google. Why? • http://wwww.google.com also returns an error message. Why?
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