What is DNS?
Definition
DNS, the Domain Name System, is the layer that turns human-readable names such as purple.ai into the IP addresses devices connect to. On guest WiFi it does more than resolve names: captive portals use it to redirect new devices, and DNS-level filtering is the basis of safe-browsing controls.
DNS explained
Every connection starts with a DNS lookup. The DHCP server tells each device which DNS resolver to use, and the device asks that resolver for the address of every site and app it contacts. Because the lookup comes before the connection, DNS is a natural control point for the network.
Captive portals rely on that. Before sign-in, the network answers or redirects DNS requests so that an unauthenticated device lands on the portal, while the walled garden lets the portal and its login providers resolve normally. Dynamic DNS resolution in the walled garden matters, because social login providers change their IP addresses often.
DNS filtering applies the same principle to safety. The resolver refuses to answer for domains known to host malware, phishing or inappropriate content, so the device never connects. It is one of the lowest-cost security controls on a guest network, it can reduce bandwidth by blocking unwanted traffic, and it helps venues enforce content policies. Encrypted DNS, such as DNS over HTTPS, is the evasion route to plan for.
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