Fully Qualified Domain Name
May 10, 2008 1 Comment
A Fully Qualified Domain Name (FQDN) is the complete and unique name of a specific computer. It consists of two parts: computer’s host name and domain name. An example would be myserver.example.com. where myserver is the unique name of the computer and example.com is the domain name. There can be many computers called myserver but there can only be one computer called myserver.example.com.
Note that myserver.example.com. has a period at the end of com. So it is .com. and not .com only. The last period differentiates between an FQDN and a regular domain name. If your domain name is longer, say firstnetwork.example.com, then myserver.firstnetwork.example.com. would be your FQDN.
In Linux, you may edit your /etc/hosts file and put your FQDN in it this way:
127.0.0.1 localhost.localdomain localhost
127.0.0.1 myserver.example.com. myserver
The above example shows that both localhost.localdomain and myserver.example.com. are FQDNs for the same server. Adding localhost and myserver at the end of these lines means we have an alias for the FQDN. This alias has to be the same as your computer’s hostname.
To really comprehend the difference between an unqualified and a qualified domain name, there is a simple test. Using the /etc/hosts as above, you could do the following:
ping -c 3 localhost
ping -c 3 localhost.localdomain
ping -c 3 myserver
ping -c 3 myserver.example.com.
All of the above examples will show the destination IP to be 127.0.0.1 and it tells you that the configuration is correct
ping -c 3 myserver.example.com
Now if you do not have myserver.example.com in the Internet DNS, doing the above will not ping any computer. (Note the absence of a period at the of domain name).