Hostname

The host name (also called the site name ) is the unique designation of a computer in a network . It is mainly used for electronic data exchange (e.g. e-mail , Usenet , FTP ) to specify the communication partner in a format that can be read and remembered by humans. The conversion of the host name into a machine-readable address takes place on the Internet today mainly via the Domain Name System (DNS) , historically via the hostsfile. In local networks the implementation takes place partly via DNS , partly still with NIS and other proprietary protocols. Which names are technically permissible is regulated by the name resolution protocol used in each case - i.e. the Domain Name System on the Internet .

Host name as the name of a physical system

The host name of a physical system ( computer , host ) is the name by which the system knows itself and with which the system reports. This host name can become visible when a computer sends a system mail, for example in the sender of status messages or bounce messages or when a user logs on to a server . The host name can be set and read out on UNIX-like systems with the hostname command.

For computers that are directly on the Internet , i. d. Usually a fully qualified domain name (FQDN) is used as the host name, e.g. B. mail.wikipedia.org. For computers that can only be reached from a LAN , the domain part (here:) is sometimes wikipedia.orgomitted and only the local part is used (here:) mail, since the domain part is not necessary in this case for clear differentiation.

The local part of the host name of physical systems can basically be chosen freely. It is often used to identify the purpose of the computer (e.g. ns, mail, ftp, serv1, serv2, serv3 etc.), but it is not uncommon for it to be arbitrary based on characters from literature and film, on mythical creatures or gods forgive.

Host name as the name of a network node

In the Domain Name System are AAAA resource records (IPv6), and A resource records entered, the one name one IP address assigned. This name can, but does not have to be, the host name that the host has with this IP address. This enables a host to be reached under different names.

Example:

A web server runs on a host and looks after several customers. The website of one can be reached via example1.de, the other via example2.de. Both names are entered in the Domain Name System with the same IP address .

The full name of a network node is usually composed of a part that describes a service (e.g. www, mail, ftp, etc.) and a domain part (e.g. wikipedia.org). However, this practice has grown over time and only makes sense if these services are provided by different hosts. Since there is no difference between domains and subdomains for the domain name system, A and AAAA resource records can also be entered directly on the domain part , e.g. B .:

user$ host wikipedia.org
wikipedia.org has address 91.198.174.192
wikipedia.org has IPv6 address 2620:0:862:ed1a::1

A distinction with reference to the host name called is usually only possible with HTTP.

Guidelines

Like all domain names , hostnames consist of several “labels” that are separated from one another by a period. Each label must be 1–63 characters long, the domain name can have a maximum of 255 characters.

In contrast to domain names, host names may only consist of the ASCII characters a- zor A- Z(no distinction is made between uppercase and lowercase letters), digits 0- 9and the hyphen minus - . The individual labels must not begin or end with a hyphen. Special characters other than the hyphen (and the period between the labels) are not permitted, although they are occasionally used anyway. Underscores are often used on Windows systems, although RFC 952 does not allow them. Some systems, such as DomainKeys and the SRV Resource Record , use the underscore on purpose to ensure that their specific domains are not confused with hostnames. Since only certain systems check the validity of hostnames, the use of invalid characters such as the underscore has led to various problems in systems connected around the world.

The host name de.wikipedia.orgtherefore consists of the DNS labels de, wikipediaand org. Labels like 2600and 3commay be used in host names, -hi-and *hi*on the other hand are invalid.

history

20th September 1971

RFC 226 - Standardization of host mnemonics

6 characters to describe a host name, in the example only capital letters and numbers are used

22nd September 1971

RFC 229 - Standard host names

8 characters to describe a host name, in the example only capital letters, numbers and hyphens are used

5th October 1971

RFC 237 - NIC view of standard host names

At least 8 characters with reference to the use of up to 12 characters for the NIC

17th November 1971

RFC 280 - A Draft of Host Names

A first draft overview of hosts with host names in the network

Up to 11 characters are used

December 21, 1971

RFC 289 - What we hope is an official list of host names

A first official overview of hosts with host names in the network

Up to 11 characters are used

December 12, 1973

RFC 597 - Host Status

An overview of hosts with host names in the network

Up to 12 characters are used

January 10, 1974

RFC 608 - Host names on-line

48 characters to describe a host name, consisting of capital letters, numbers and the hyphen

March 1, 1982

RFC 810 - DoD Internet host table specification

24 characters to describe a host name, consisting of capital letters, numbers, the hyphen and a period

October 1985

RFC 952 - DoD Internet host table specification

The point may only be used to separate domain names from one another

October 1989

RFC 1123 - Requirements for Internet Hosts - Application and Support

Hostname resolution software must support up to 63 characters and should support up to 255 characters

Individual evidence

↑ All you need to know: what is a hostname? Retrieved August 25, 2020