FQDN — Fully Qualified Domain Name
Qué es FQDN?
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An FQDN (Fully Qualified Domain Name) is a complete, unambiguous domain name that identifies one exact host on the internet — like `smtp.example.com` — by naming every label up to the root of the DNS tree. Communication platforms use FQDNs wherever configuration must point at one specific endpoint: the mail server in an MX or SPF record, the SIP server a trunk registers with, and the TLS certificate a connection verifies are all looked up by their fully qualified names.
More detail
An FQDN names every label from the host up to the DNS root — host, subdomain, domain, and top-level domain — so `sip.devotel.io` fully identifies one host, while a partial name like `sip` could match many domains. When DNS is configured with an FQDN, resolution is deterministic: the lookup returns the same host for every client, which is why MX records, SPF include mechanisms, and SRV records all reference FQDNs rather than relative names.
In voice and email setup the FQDN does double duty. A SIP trunk registers to a provider's FQDN and authenticates the TLS certificate against that exact name. Email authentication (SPF, DKIM, DMARC) and MX routing all bind sender identity to FQDNs, and reverse DNS checks that the sending IP's PTR maps back to one. Because a certificate, record, or registration pinned to an FQDN fails on any other name, keep the name stable even when the IP behind it moves.
Preguntas frecuentes
- FQDN vs. a regular domain name — what's the difference?
- A regular (partial) domain name may omit labels and depend on a DNS search domain to resolve, so it can be ambiguous. An FQDN carries the full label path from host to root, so it always resolves to the same specific host.
- Where do I see FQDNs when setting up SIP trunks or email?
- SIP trunks register to the provider's FQDN and validate the TLS certificate presented for that name; email setup references FQDNs in MX, SPF, and DKIM records, and reverse DNS maps the sending IP back to an FQDN for sender-authentication checks.
See also
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