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So whenever I am in hotels (or other public networks) after I connect to the hotel network a browser window opens with a logon page or customer agreement.

How does Windows know to open a webpage when connecting to the network?

user1028270
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  • The browser window opens up automatically? I expect DNS fakery to forward the request to the hotel log in site instead of the page you are requesting. but only after you open the browser – ratchet freak Dec 01 '16 at 16:26

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Windows detects that there is an Captive Portal and lauches the browser. The page loaded is from the router of the establishment that redirects all http requests to their own webserver who hosts the login page. That way it is transparent to the end-user.

Once you have logged in, the router will then act as a proxy and let your requests go to the internet normally.

These systems are called Captive Portals. Here is the Wikipedia article on them: https://en.wikipedia.org/wiki/Captive_portal

Microsoft Windows does in fact automatically open a broswer window when it detects captive portals. Here is the MSDN article that describes this: https://msdn.microsoft.com/en-us/library/windows/hardware/dn408681.aspx

IronWilliamCash
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  • Immediately after connecting to the network windows opens a webpage (without user interaction). Something has to happen to trigger that, its kicking off a web-request or something no? I should say I'm familiar with how the proxy works, just don't get how a webpage opens as soon as I connect. – user1028270 Dec 01 '16 at 16:28
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    Windows probably detects that there is a Captive Portal and prompts you because it is not able to connect to it's normal services. I added the link to the Wikipedia article on captive portals in my answer. – IronWilliamCash Dec 01 '16 at 16:30
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    Yes it seems what when Windows detects captive portals, it opens a Window automatically. I added this too to my answer. – IronWilliamCash Dec 01 '16 at 16:32
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    Ah ha! That's pretty cool, also looks like this was a new feature starting with Windows 8: https://msdn.microsoft.com/en-us/library/windows/hardware/dn408681.aspx – user1028270 Dec 01 '16 at 16:34
  • Glad I could help! – IronWilliamCash Dec 01 '16 at 16:36