DNS

DNS (Domain Name System) translates human-readable names — a website or server address — into the numeric IP address a device actually needs to connect. Without DNS, every service would need to be remembered as a string of numbers instead of a name. That translation is handled by a DNS server, either supplied automatically via DHCP or configured manually on the device.

In practice, a device looking up a name first asks its configured DNS server, which either already knows the answer — for instance from an internal company directory — or looks it up from a higher-level DNS server on the internet. Many businesses run their own internal DNS server so internal systems, such as a file server or camera software, can be reached by name rather than by IP address. Answers are cached for a period of time, so not every lookup has to travel the full path again.

A common failure mode is a stale DNS cache: if an internal service's IP address changes but the old entry is still cached somewhere, that service appears unreachable to some devices for no obvious reason. Internal and public DNS also get mixed up regularly — a name meant to resolve only inside the company network naturally won't resolve from outside it.