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Most of the websites and servers that you can connect to on the
Internet are known to you by a hostname, such as
www.umd.edu. However, the Internet does not really use
these hostnames to access such sites.
The set of rules for communicating on the Internet, Internet
Protocol, or IP, call for the machines hosting these
sites to
be identified to by a specific IP addresses, which is 4
sets of numbers separated by periods, For example:
128.8.76.2. So if you request a web page with a hostname,
that hostname somehow must be
translated into its numeric IP form. Until that occurs,
your "real" request cannot be completed.
Finding this address is the responsibility of the machines in the world-wide
Domain Name System hierarchy, or
DNS.
A domain is a name representing the institution,
organization, person, or company that
paid to register that name with a domain registrar. Examples include:
- whitehouse.gov - The White House
- umd.edu - The University of Maryland
- washingtonpost.com - The Washington Post
Whoever provides Internet service for a domain provides it with one or more IP
addresses. The University of Maryland, for example, has many IP addresses in blocks within
two numeric ranges that start with 128.8. and 129.2. and several others.
It is a policy of the University to have a hostname associated with each IP address
that is in use. This is not an Internet requirement, however, and many domains do not do
so. A good example of this would be an Internet Service Provider (ISP)
that provides
internet service in which each customer gets temporarily assigned an IP address from a pool
of addresses maintained by the ISP. If the ISP is rapidly expanding and is constantly adding new
blocks of addresses, it may choose not to take the trouble of giving each address an
actual hostname.
The Domain Name System is a hierarchical naming
system for computers, services, or any resource participating in the
Internet. It associates various information with domain names assigned to
such participants. Most importantly, it translates domain names meaningful
to humans into the numerical (binary) identifiers associated with networking
equipment for the purpose of locating and addressing these devices
world-wide.
An often used analogy to explain the Domain Name System is that it
serves as the "phone book" for the Internet by translating IP addresses
into human-friendly computer hostname, e.g., 128.8.237.77 to www.umd.edu.
For more detailed information on DNS and domains, see Wikipedia's entry.
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