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The domain name system (DNS)
Skills: none
IT concepts: domain, domain name, host, IP
address, domain registrar
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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?
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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?
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•
•
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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:
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.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:
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•
•
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.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
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•
•
•
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
155.135.1.163
ctl.csudh.edu
155.135.1.166
email.csudh.edu
155.135.1.180
ns1.csudh.edu
155.135.55.2
vaquero.csudh.edu
155.135.55.6
toro3.csudh.edu
155.135.55.8
music1.csudh.edu
155.135.55.11
home.muphiepsilon.org
155.135.55.13
library.csudh.edu
155.135.55.17
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
155.135.1.163
ctl.csudh.edu
155.135.1.166
email.csudh.edu
155.135.1.180
ns1.csudh.edu
155.135.55.2
vaquero.csudh.edu
155.135.55.6
toro3.csudh.edu
155.135.55.8
music1.csudh.edu
155.135.55.11
home.muphiepsilon.org
155.135.55.13
library.csudh.edu
155.135.55.17
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?