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How does Android devices automatically prompt for Guest portal page?

  • 1.  How does Android devices automatically prompt for Guest portal page?

    Posted 12-13-2019 06:20 PM
    • In many cases, it is desirable to provide a  Guest Network where the User is logged in as a Guest and is automatically redirected to the Welcome Page. This provides a User-friendly way of displaying a Guest Portal Login prompt to the User when they connect to the Guest Network. 
    • Once an Android Device is connected to a Captive portal network, it will try to reach the URL http://connectivitycheck.gstatic.com and it expects a response.
    • The device will try to send a HTTP Get request to the URL and AP will spoof the connection and respond with a 302 Redirect (http://captive-2019.aio.cloudauth.net/swarm.cgi), on behalf of http://connectivitycheck.gstatic.com.
    • The redirected URL will provide the splash page to the User.
    • Below Wireshark capture represents the flow of automatic prompt for Guest Portal page.















    • Once the Authentication is complete, whenever the Guest Client contacts http://connectivitycheck.gstatic.com, the AP will not spoof the TCP connection.
    • The Guest Client will hence not get a 302 redirect message from http://connectivitycheck.gstatic.com, but will get a HTTP 200 Ok.
    • The Guest Client will then assume that there is no Captive Portal Authentication configured on the Wireless Network or the Captive Portal Authentication is successful.