A captive portal is a web page that a network shows to newly connected users before granting full internet access. It is common on hotel, airport, cafe and guest Wi-Fi, where you must accept terms, enter a voucher code or log in.
Why it matters
The network lets the device join and obtain an address via DHCP, but a gateway then blocks most traffic and redirects web requests to the portal. After the user completes the step, the gateway records the device (often by its MAC address) as authorized. Operating systems detect portals by requesting a small known URL; if the reply is a redirect instead of the expected content, they pop up a sign-in window.
Because it works by interception, a portal can break things: HTTPS sites cannot be redirected without certificate errors, and apps or VPNs may fail until the login is done.
Example
You join Hotel-Guest and your phone shows "Sign in to network". Behind the scenes, its connectivity check to a test URL returned a 302 redirect to http://portal.hotel.example/login. After you enter your room number, the next check succeeds and normal browsing works.
Common mistakes
- Trying to browse an HTTPS site first and treating the certificate warning as an attack, or ignoring it on a real attack.
- Starting a VPN before completing the portal login.
- Assuming a portal login makes the network secure; the traffic may still be open.
Related
Get notified when this term updates
Plus occasional practical tips on uptime and monitoring, nothing else. Unsubscribe anytime.
This page is general information written by our editorial team and updated when documentation changes. Servers and providers differ, so test changes safely first. See our editorial policy and disclaimer.