The captive portal technique forces an HTTP client on a network to see a special web page (usually for authentication purposes) before surfing the Internet normally. This is done by intercepting all HTTP traffic, regardless of address, until the user is allowed to exit the portal. You will see captive portals in use at most Wi-Fi hotspots. It can be used to control wired access (e.g. apartment houses, business centers, "open" Ethernet jacks) as well.

Examples of captive portal software packages are:

• FirstSpot (Windows)
• m0n0wall (embedded FreeBSD)
• NoCatAuth (Linux)
• OpenSplash (FreeBSD)
• wicap (OpenBSD)
• Other wiki list of captive portals

See also

• HTTP proxy