In this article, we will see the Captive portal HTTP/Radius information flow as below.
Note: I did not include the DNS information flow in the above.
Most of the captive portal setup will ask to accept Terms & conditions to have Internet access. On the below page, once you tick the checkbox before accept Terms & Conditions and hit the button "Log in," the user will have Internet access.
The captive portal server's web page will automatically create a username and password for each user device used to track the user device.
Below are the frames captured between the user Device and Access point.
Frame -1: Shows the User connected to the SSID and trying to access the internet.
Frame-2: As the user is not Authenticated or did not accept the Terms & Conditions, the user is redirected captive portal page.
Frame-3: We can see the User trying to access the captive portal page from the Captive portal server ( "server-ip/guest/test-cp.php" is the page URL).
If the Page/captive portal server is not reachable at this stage, we will see an Error saying too many redirects.
Frame-4: Once the page is accessible and the user ticks the checkbox to accept Terms & Conditions and hits Log in button, the web page will automatically create a username and password for each user device. Post/Login frame helps a lot in troubleshooting the captive portal problems.
Once Post /login frame reaches the Access point with the information available on the page, a radius Access request is formed and sent to Radius Server by the Access point.
Frame-5: After Successful authentication user is redirected to Linked.com. If the reachability to the captive portal server and radius are ok, the user should not face any issues in going online.