What package triggers the captive portal?

[73agordon]

What exactly triggers the captive portal page to load?  I know it is supposed to load if a user tries to access internet. Does the DNS request trigger the portal, or is it something else?

[jimp]

When the user tries to access a page, if their MAC isn't listed as being logged in, they are directed to the portal page instead of whatever they tried to load.

DNS is needed because unless a client can resolve a hostname, it will never try to load a page, and thus would never hit the portal.