Unable to understand the connections between FQDN and DNS

domain-name-systemfqdn

I am unsure what the following sentence in bold means

If you are using only the hostname
(without the domain information) to
connect to a server, the application
you're using may not be able to
resolve the hostname. This can happen
if either the DNS suffix search order
in your computer's TCP/IP properties
is incorrect, or the DNS table is
corrupted. In these cases, entering
the host's FQDN will allow DNS to
locate the server. —

I know that FQDN means the following in www.mySite.com

  1. www is the 1st domain
  2. mySite is the 2nd level domain
  3. com is the 3rd level domain

I know that DNS stands for Domain Name server. It seems that DNS is the collection of FQDN.

What does the sentence in bold mean exactly?

Best Answer

You're not quite right about FQDN.

  1. It stands for Fully Qualified Domain Name, i.e. the entire domain name, not a prefix.
  2. Your parsing of your domain name is backwards. com is the top-level domain, mySite is the second-level domain, and www is almost certainly not a domain at all, but a hostname within the domain mySite.com.

What the sentence means is that if the settings that allow a 'partial' domain to be completed (i.e. you enter www, it figures out you mean www.mySite.com) are screwed up, you can work around this by entering the full domain.

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