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URLs & domains

Domain

A domain name is a text label such as example.com that identifies a host on the internet and maps, through the Domain Name System (DNS), to an IP address. In SEO, the domain is the base of every URL of a site.

How is a domain name built?

A domain name consists of labels separated by dots and is read from right to left. The rightmost label is the top-level domain (TLD), such as com. The label to its left is the second-level domain, which is the part a site owner registers. Everything further left is a subdomain, for example blog in blog.example.com. The owner of a domain can create subdomains without further registration.

RFC 1035 limits each label to 63 octets and a complete name to 255 octets in the format used on the wire. In the dotted text form this equals at most 253 characters, because the length octets and the terminating root label count toward the 255.

Anatomy of a URLThe example URL https://shop.example.de/shoes/sneakers/?color=red&page=2#reviews broken into parts: scheme https, host shop.example.de with subdomain shop, domain example.de and top-level domain de, path /shoes/sneakers/ with a trailing slash, query string with two parameters color=red and page=2, fragment reviews. The fragment is not sent to the server.Trailing slashhttps://shop.example.de/shoes/sneakers/?color=red&page=2#reviewsSchemeHostPathQuery stringFragmentSubdomainDomainParameterParameterTLDcountry code: ccTLDstays in the browser, is notsent to the serverSchematic. Scheme, host, path, query and fragment are components defined in RFC 3986.Subdomain, domain and TLD split the host by DNS level. Without a port, https uses port 443.
A URL broken into its parts. RFC 3986 defines scheme, host, path, query and fragment. Only the browser evaluates the fragment after #, it is not sent to the server. Sources: RFC 3986: Uniform Resource Identifier (URI), Generic Syntax; MDN: What is a URL?; MDN Glossary: TLD.

Registration

Domain names are registered through a registrar, usually for a fixed term that can be renewed. During registration the registrant names the authoritative name servers that answer DNS queries for the domain. The registration itself says nothing about hosting: the domain only points to wherever the name servers send visitors.

Domain, URL and website

A domain is one component of a URL. In https://www.example.com/shoes/, the domain is example.com, www is a subdomain, and /shoes/ is the path. A website is the content served under a domain, so one domain can serve several websites on different subdomains, and one website can be reachable under several domains.

Example

Text
https://shop.example.co.uk/boots/
        └──┬──┘ └────┬────┘└┬┘
      subdomain  registered  TLD
                  domain

Common mistakes

Google’s site move documentation names mistakes that are avoidable when a domain changes.

  • Redirect chains. According to Google, Googlebot follows up to 10 hops in a chain. Google recommends redirecting straight to the final destination, or keeping the chain to no more than 3 and fewer than 5 redirects.
  • Redirecting all old URLs to the home page. Redirecting many old URLs to one irrelevant destination can confuse users and might be treated as a soft 404.
  • Leaving preparation blocks on the new site. noindex rules or robots.txt blocks that only served the preparation must be removed after the move. The rel="canonical" annotations on the new site must name the new URLs.
  • Reporting only one variant of the old domain. For a domain move, Google asks for a Change of Address for all verified variants of the old domain, including subdomains and the www and non-www versions.
  • Removing the redirects too early. Google advises keeping them for as long as possible, generally at least 1 year.

Common questions

What is a subdomain? A label added in front of a registered domain, such as shop.example.com. Search engines can treat it as part of the same site or as a separate one depending on how it is set up.

Is a domain the same as a website? No. The domain is the name; the website is the content delivered under it.

Sources

  1. RFC 1035: Domain Names, Implementation and Specificationrfc-editor.org
  2. Domain name – Wikipediaen.wikipedia.org
  3. Domain name basics – Google Workspace Admin Helpknowledge.workspace.google.com
  4. Site move with URL changes – Google Search Centraldevelopers.google.com

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