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Fully Qualified Domain Name

Fully Qualified Domain Name

Fully Qualified Domain Name is the information which is used to convert a web address into a physical address. In this article, we will learn more about it.
Techspirited Staff
What is FQDN?

Fully Qualified Domain Name (FQDN) is a domain name which specifies its exact location in the tree hierarchy in Domain Name System (DNS). It is also known as 'absolute domain name'. It is a complete domain name for a specific computer on the Internet. It is made up of two parts, the host name and the domain name. Technically speaking, if there is a top-level domain 'A', it contains a sub-domain 'B' which in turn contains a sub-domain with the name 'C'. The full domain name in this case will be 'C.B.A'. This will become the FQDN for the node. The term 'qualified' stands for 'specified'. In other words, the domain name 'C.B.A' is fully qualified, as it gives the full location of the specific domain which bears its name with the entire DNS name space.

We can take an example to understand this. A hypothetical mail server can be myspace.someorganization.com. The host is myspace and this host is located within the domain someorganization.com. This domain name is fully qualified, hence the host is uniquely identified, although there may be numerous resources in the world named myspace, there is only one myspace.someorganization.com. To make it more clear, FQDN specifies all the domain levels, inclusive of the top-level domain, that is relative to the root domain.

When you are connecting to a host, you will need to specify the FQDN. The DNS server then resolves the host name down to its IP address by looking at the DNS table. The host is then contacted and you get the page you are looking for. In case you are only going to use the host name to connect to a web server, the application that you are using may not be able to resolve the host name. This happens due to either one of the two conditions. The first reason is that the DNS suffix search order in the computer's TCP/IP properties is not correct. The other reason is that the DNS table is corrupted. In such cases, when the host's FQDN is entered, it will enable the DNS to locate the server. When you are trying to connect to a remote host, which is not local to your Internet service provider (ISP), you will have to use the FQDN.

How to Find FQDN?

When you want to find the FQDN of a system, go to the Windows command prompt. In the command prompt enter:

IPCONFIG/ALL

When you want to create one, concatenate the values of and as follows:

.

The IP configuration, for example will be:

Host Name . . . . . . : MYSERVER
Primary DNS Suffix . . . : mydomain.Great-Works.com
This in turn can be equated to the Fully Qualified Domain Name:
MYSERVER.mydomain.Great-Works.com

Errors

If you are restarting your Apache server, do you get an error which reads, Could not determine the server's fully qualified domain name, using .... for ServerName?

In this case, you will have to log into your Redhat server with the SSH account which was given by the staff. When you are logging in, make sure you are logged in as root. In case you have forgotten your password, you will have to get in touch with the support team. Once you have the password, follow the steps mentioned below. Type echo HOST.DOMAIN.com > /etc/hostname.

The HOST will be your host name and the DOMAIN will be your domain name. The next command to be executed will be /bin/hostname -F /etc/hostname

Once you have the host name and the domain name in place, restart the server with /etc/init.d/httpd restart command, you will not see the error any more. I hope this information proves to be useful to you.