Web traffic
A common method is to direct all World Wide Web traffic to a web server, which returns an HTTP redirect to a captive portal. When a modern, internet-enabled device first connects to a network, it sends out an HTTP request to a detection URL predefined by its vendor and expects an HTTP status code 200 OK or 204 No Content. If the device receives a HTTP 200 status code, it assumes it has unlimited internet access. Captive portal prompts are displayed when you are able to manipulate this first HTTP message to return a HTTP status code of 302 (redirect) to the captive portal of your choice. specifies 511 Network Authentication Required code.