Hi Rajesh Shanmugasundaram
A fully qualified domain name (FQDN) is the complete domain name for a specific computer, or host, on the Internet. The FQDN consists of two parts: the hostname and the domain name. For example, an FQDN for a hypothetical mail server might be mymail.somecollege.edu. The hostname is mymail, and the host is located within the domain somecollege.edu.
In this example, .edu is the top-level domain (TLD). This is similar to the root directory on a typical workstation, where all other directories (or folders) originate. (Within the .edu TLD, Indiana University Bloomington has been assigned the indiana.edu domain, and has authority to create subdomains within it.)
The same applies to web addresses. For example, www.indiana.edu is the FQDN on the web for IU. In this case, www is the name of the host in the indiana.edu domain.
When connecting to a host (using an SSH client, for example), you must specify the FQDN. The DNS server then resolves the hostname to its IP address by looking at its DNS table. The host is contacted and you receive a login prompt.
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. Also, if you are trying to connect to a remote host that is not local to your Internet service provider (ISP), you will probably have to use the FQDN. For example, it's unlikely that a DNS server at IU would have a listing for remote hosts at another university or an unrelated ISP.
A fully qualified domain name consists of a host and domain name, including top-level domain. For example, www.webopedia.com is a fully qualified domain name. www is the host, webopedia is the second-level domain, and.com is the top level domain.
A FQDN always starts with a host name and continues all the way up to the top-level domain name, so www.parc.xerox.com is also a FQDN.
A fully qualified domain name (or FQDN) is an unambiguous domain name that specifies the node's position in the DNS tree hierarchy absolutely. To distinguish an FQDN from a regular domain name, a trailing period is added. ex: somehost.example.com. An FQDN differs from a regular domain name by its absoluteness; a suffix will not be added.
For example, given a device with a hostname of "myhost" and a domain name of "example.com", the fully qualified domain name is "myhost.example.com.". It therefore uniquely defines the device — whilst there might be many hosts in the world called "myhost", there can only be one "myhost.example.com.".
Notice that there is a dot at the very end of the domain name, i.e. it ends ".com." and not ".com" — this indicates that the name is an FQDN. For example "myhost.bar.com" could be ambiguous, because it could be the prefix of a longer domain name such as "myhost.bar.com.au", whereas "myhost.bar.com." is a fully qualified domain name. Technically, the dot comes before the empty label indicating the root of the Domain Name System hierarchy, and so an FQDN is sometimes called a rooted domain name. In practice, the dot is almost always omitted in everyday applications, making such domain references technically ambiguous.
The maximum permitted length of an FQDN is 255 bytes, with an additional restriction to 63 bytes for each label within the domain name. The syntax of domain names is discussed in various RFCs — RFC 1035, RFC 1123 and RFC 2181. Any binary string can be used as the label of any resource record; a common misconception is that names are limited to a subset of ASCII characters.
Internationalized domain names expand the character repertoire of domain names to include non-ASCII characters, by encoding Unicode characters into byte strings within the normal FQDN character set. As a result, the character length limits of internationalized domain names are content-dependent.
A FQDN is not the same as a Uniform Resource Locator (URL) as it lacks the protocol name to be used in communication with the host. A URL always starts with "<scheme>:", and so includes the communication protocol (like "http:", or "ftp:"), and includes information specific to the scheme, such as a directory path, a filename and a TCP port number.
Sometimes FQDNs are specified by the user instead of the full URLs. An example would be typing www.ebay.com into the URL bar of a browser. In this case, the protocol is assumed to be HTTP on TCP port 80; nearly all web browsers use this as the default if not otherwise specified.
cheers!
gyanaraj
****Pls reward points if u find this helpful
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