How did a Captive Portal force to open a browser

Question

I've setup a Captive Portal with dd-wrt, wifidog, authpuppy and some plugins from authpuppy as well as my own web app.

1. I am wondering what's the exact thing that will trigger a browser on the client device to popup?
2. Is the popup browser from iPhone/iPad a regular browser mode?
   
   • It seems some JavaScript will fail on the browser mode, like the shake.js, event though iOS Safari version is > 4.2.1 from https://github.com/alexgibson/shake.js/

P.S.:

I've done the research like

• http://en.wikipedia.org/wiki/Captive_portal
• https://personaltelco.net/wiki/CaptivePortal

they don't talk much about the popup browser.

Could anyone help?

Solution

If you will try to see the network statistics [request/response] you will find out that devices like ios and android both of them continuously hits some particular urls [in case of android it is www.google.com/generate_204 , don't remember exact url for ios]. These url are generated by system internally. These pings let their server know about various details. So as soon as ios gets connected with a captive portal it tries to hit the system generated url, failing to which it understands that this is packet level protected network and open the browser.

Hope this helps.