Domain Names and Numbers

in Internet nodes can have names as well as numbers

• increase ease of use:

  Which is easier to remember?

  123.456.78.90 or www.mysite.com

• examples:

  www.cs.cf.ac.uk
  online.sunsolve.sun.co.uk
  matups.matups.fr
  nic.switch.ch
  faui80.informatik.uni-erlangen.de
  export.lcs.mit.edu
  gatekeepr.dec.com

Figure: Internet Addresses

However we need to map between names and numbers

• Domain Name Service (DNS)
• distributed database of names and numbers
• hosts run DNS program or know where to find one
• local mapping done by local DNS host
• remote hosts associated with remote DNS

Domain Names Explained

Now we'll examine the name itself.

• Domain names have at least two parts, separated by a dot or period.
• The rightmost part after the dot is called the Top Level Domain (TLD).

  The Top Level Domain serves to broadly categorize the name as to its type or purpose.

• Common TLDs include:

  .com

  -- Commercial organisation worldwide (mainly US),

  .org

  -- Organizations worldwide (mainly US) ,

  .edu

  -- US educational institutions,

  .net

  -- US networks, Public service, state-run offices in general

  .gov

  -- U.S. government

  .mil

  -- U.S. military.

  .int

  -- International organisations.

  For example netscape.com, mit.edu, nasa.gov.

• There are also hundreds of country TLDs, such as:

  .uk

  -- UK,

  .us

  -- USA,

  .fr

  -- France,

  .de

  -- Germany, etc.

• Additional generic TLDs (gTLDs) have been proposed. Domain names ending in .firm, .store, .web, .arts, .rec, .info, .nom and possibly many others will become widespread on the Net.

• The part of the domain name before the dot is the Second Level Domain (SLD).
• In the UK you can categorise institutions via the last but one rightmost field (.uk) will be the rightmost:

  .ac.uk

  -- Academic institutions.

  .co.uk

  -- Commercial organisations.

• Further left SLDs identify locations and institutions and maybe host machines. For example:

  cs.cf.ac.uk

  -- the Computer Science (cs) dept and Cardiff ( cf) University (ac) in the U.K. (uk).

  bbc.co.uk

  -- BBC bbc, a company (co) in the U.K. (uk).

  albia.museo.csic.es

  -- Host machine (albia) at Natural History Museum museo, Spain(es).

  spacelink.msfc.nasa.gov

  -- Host machine called spacelink at Marshall Space Flight Center (msfc, which part of NASA (nasa) which is part of the U.S. federal government gov.

• Databases of domain records are maintained by InterNIC, the primary name registry on the Internet in the US, and by a variety of similar agencies throughout the world. Accessed through a utility program called WHOIS, these databases are easily accessed from throughout the Net.

There's a list below of sites that provide a WHOIS "gateway" for queries of domain name databases from your Web browser.