Explain Required Sign In Forms For Wifi Access Like I'm Five

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Hello there!

I've always wondered how some wifi connections require you to sign in or fill out a form on a page before you can freely access the internet. How is this effect implemented?

I know little about the actual hardware and the networking that may or may not be involved.


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In the case of the captive portal I made for a local cafe, the "Guest Network" allows a certain range of IP addresses. This would contain the web page/app that lets you "sign in" to the AP. After signing into the AP you now have a different range of IP addresses you can access (or be denied from!)

I used Unifi in my implementation. The interface to configure this via unity can be seen here (I just binged "unifi guest" this is not my config)



Thanks damian! This was a good explanation!


Captive portal logins, it's such a pain not only because I have to do this with almost every cafe I work out of daily, but also because my wifi at home requires this for all my devices, and some devices don't have the cookies/cache to save my login info..


I spent hundreds of dollars a year to use Wi-Fi outdoors, but save money for home use hehe


Originally they used a bunch of tricks to intercept traffic. But with the up-rise of HTTPS and HSTS these tricks fail a lot. The solution has move however, OS and browsers perform a special DNS lookup to a domain withing their control. If this does not return the expected response the OS/Browser assumes it is the host of the portal.

Here is a more detailed explanation for Windows 7 and probably later version.

And this one is for Firefox.


Hehe yeh. I've never really had the experience saying "Ahh I really love these forms". However, I do realize the benefits of data collection by doing these things. I just personally never been in a position like that :P

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