Subdomener

Subdomener are subdivisions of a domain name used to organize resources, host services, or delegate administration within the Domain Name System (DNS). Each subdomener forms a hostname that is part of the parent domain, for example, api.example.com or blog.example.net. Subdomener can be managed in two general ways: by adding records to the parent domain’s zone file to define the subdomain, or by delegating the subdomain to a separate DNS zone controlled by a different administrator via NS records.

DNS records for a subdomener can include A or AAAA records that map to an IP address, CNAME records that alias to another host, MX records for mail, or TXT records for verification and policies. A subdomener may have its own set of records and can be served by a different hosting provider or DNS service than the parent domain.

Common use cases include hosting separate services (blog, API, store) under distinct subdomener, geographic or language variants (eu.example.com, en.example.org), and multi-tenant architectures. Subdomener also enable granular DNS delegation and easier migration of individual services without affecting the entire domain. However, having many subdomener increases management overhead, complicates SSL/TLS coverage, and can impact cookies and performance.

Security considerations include protecting DNS control, monitoring changes, and implementing DNSSEC to reduce spoofing risk. A potential risk is subdomain takeovers if a subdomener points to a service that is later decommissioned.

See also: Domain name system, DNS records, NS records, DNSSEC, wildcard subdomains.