The host name is unique



Illustration: Hostname - Author: Seobility - License: CC BY-SA 4.0

In computer networks, the host name is the term used to uniquely identify devices such as computers or servers in a network. Host names are used in both local area networks (LANs) and wide area networks (WANs) such as the Internet. The assignment of unique host names helps users to identify different devices in a network. The host name consists of a simple sequence of alphanumeric characters and, if applicable, a hyphen.

In the context of websites, the domain name is appended to the actual host name in order to guarantee a clear assignment. The domain is separated from the host-specific name by a point. For the url would be the domain name and www the hostname. www is commonly used as the host name for web servers. Another possible host name would be, for example m as a name for servers that display websites for mobile devices. The designation mail however, it is often used as a name for mail servers.

If the domain name, including the top level domain (.com), is fully specified as above, it is referred to as a fully qualified domain name, abbreviated to FQDN for "Fully Qualified Host Name".

FQDNs that contain a DNS domain are stored together with the IP addresses of the host they represent in the Domain Name System, the DNS, so that the domain can be assigned an IP address or vice versa.

How hostnames work

Since the dawn of network technology, it has been considered user-friendly to assign a host name to a computer or server while the computer retains its internal host address, i.e. the host portion of an IP address, or network address. The real "name" a computer needs to communicate on a network is actually just a series of numbers, the IP address. The first computers on the Internet used small integers as the host address. One of the earliest Internet RFCs, "Standardization of host mnemonics", lists the table of associated host numbers and host names for the first Internet computers in a file called HOST.TXT stored on every computer that wanted to communicate with other computers on the web.

While the original file wasn't very long, with only 20 entries, it quickly became apparent that this solution wasn't scalable or flexible enough to handle the rapidly growing number of hosts connected to the Internet. In addition, such a file would have to be created and maintained individually on each computer. To counteract these problems, the DNS was developed.

The Domain Name System is comparable to a telephone book. In the DNS, every IP address required for communication between network computers is linked to a name that can be read and remembered by humans. For TCP / IP, the family of protocols on which the Internet is based, every computer has a network IP address that follows a specific syntax to ensure its uniqueness and validity. An IP address alone says nothing about the function of a computer within a network. To make it easier for users to assign them, each computer is given a host name.

Guidelines for assigning hostnames

Local network hostnames do not have a standard format and can be assigned relatively freely from conventions. Exceptions are spaces and special characters such as commas, periods and apostrophes, these must not be included.

The rules for public hostnames were first standardized in the original hostname specification "DoD Internet Host Table Specification". The standard said that the name should be a text string consisting of the letters A through Z (upper or lower case), the digits 0 through 9, the minus sign (-), and the period (.). To date, no spaces are allowed as part of a name. The first character had to be a letter and the last character could not be a minus sign or a period. It was also recommended not to exceed 24 characters.

This protocol, known as RFC 953, was replaced in 1989 by the newer standard RFC 1123. Since then, the first character can be either a letter or a number, the name of the domain cannot end with a hyphen and the length can be up to 255 characters.

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