Sousdomaine

Sousdomaine, known in English as subdomain, is a hostname that exists within a larger domain in the Domain Name System (DNS). For example, blog.example.com is a subdomain of example.com. In French contexts the term is sous-domaine; in English texts the equivalent is subdomain. Subdomains help organize services and hosts under a common second-level domain.

In the DNS hierarchy, a subdomain is created by adding a label to the left of the parent domain. The DNS records for the subdomain can live in the same zone as the parent, or the subdomain can be delegated to its own DNS zone with separate NS records. Delegation enables independent administration and different hosting or certificate configurations while remaining part of the same domain name.

Common uses include hosting distinct services under the same domain (for example, blog or shop), creating staging environments, or organizing content for multi-tenant services. Subdomains are distinct from subdirectories: the former is a separate hostname, while the latter is a path under the same hostname. This distinction influences branding, analytics, and SEO strategies.

Management considerations include DNS records (A, AAAA, CNAME, TXT, and MX where appropriate) and TLS certificates. Wildcard certificates can cover all subdomains of a domain, but granular certificates are often preferred for security and maintenance. DNSSEC may be used to protect zone data from tampering.

Related topics include DNS, DNS records, wildcard subdomains, and TLS certificates.