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

#explainlikeimfive #curious #wifi #how

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.

Thanks!

Top comments (10)

damian • Apr 26 '19

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)

community.ubnt.com/ubnt/attachment...

Edwin Mak • Apr 27 '19

Thanks damian! This was a good explanation!

tommy • Apr 26 '19 • Edited

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..

Edwin Mak • Apr 26 '19

Bummer :(

tommy • Apr 26 '19

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

Michiel Hendriks • Apr 28 '19

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.