What is a hostname?

A hostname is the unique identifier of a server service available on a network. On the internet it is combined with a domain name to create a useful hierarchy which can be split and used in various ways. The full name of a service location can also be used as part of a URL.

In general a unit of computer hardware (with a network connection to an IP network) can have many hostnames. These can be aliases or unique names mapped to IP addresses or different services on the hardware. On the web we speak of hostnames as part of the URL, the universal resource locator.

If you take a closer look at the structure of a URL, the hostname is the part between the protocol, e.g. https://, and the first /, which appears directly after the top-level domain. The hostname is thus made up of the following elements:

  • Subdomain: “www.”
  • Domain or domain name: “youtube.com”
  • Top-level domain: “.com”, or a country code like “.de”
Hostname Image 1 SISTRIX

The hostname in the above URL is shown in the second (3) bracket.

Hostnames need to be read from right to left in order for the hierarchy to be properly understood. Individual elements are separated by dots:

com > youtube > www

A hostname can consist of many sub-domains. For example, www.motorace.blogspot.google.com. In theory, a hostname could include 126 levels of subdomain.

In terms of the internet domain name system a hostname is only the leftmost part of the structure and this can lead to some confusion between those that work on IP architecture, and those that work in the web sector.

In local networks or on standalone computers, a hostname can be the locally configured name of a computer. For example, configured in the /etc/hostname of a Linux, Unix or similar computer.

Distribution of strength, and problems

The right-most label is the top-level domain, .com, and each label to the left specifies a subdivision, or subdomain, of the domain to the right. Generally, this is the direction in which Google distributes strength and possible problems.

If you have a strong domain, you can also transmit the trust value to all subdomains. Obviously the top-level domain, .com in this case, is not taken into consideration.

In the case of possible penalties, the whole thing works in the same way, with transmission based on the hierarchy line. It is interesting to note that penalties are not passed on from subdomain hostnames to the main domain. This means that there is the potential to ‘catch something’ on spam.example.org without having to worry about the main domain, as long as there are no manual penalties.

However, the same applies to the trust signals that a certain hostname of a domain accrues. Without a corresponding distribution via internal links to the domain, trust will also not be passed from the subdomains to the main domains.

Steve Paine