# Captive portal

> The page that pops up on public Wi-Fi asking you to log in or accept terms first.

- Level: Basic
- Topics: Networks
- URL: https://tidbit.legios.com.ar/captive-portal/
- In Spanish: [Portal cautivo](https://tidbit.legios.com.ar/es/captive-portal/)

A **captive portal** is the web page you see when you join the Wi-Fi at an airport, hotel, café or hospital and it asks for your room number, an email address, a code from your ticket, or just a tap on "Accept". Until you get past it, you are connected to the network but not to the internet: you are held "captive" on that one page.

Behind the scenes, the network's gateway lets your device in but blocks or redirects all your traffic. Phones and laptops detect this on their own: right after joining, they try to load a known test address (Apple, Google and Microsoft each have one). If the answer is not what they expect, they conclude there is a portal and open a small login window automatically. Once you accept, the gateway remembers your device, usually by its MAC address, and lets your traffic through for a while.

Captive portals are useful to venues: they can show terms of use, charge for access, limit time, or collect an email for marketing. They are also a weak spot. The page itself is often not protected by HTTPS, and anyone can set up a fake hotspot with a convincing login page to steal passwords. A good habit is never to type an important password into a Wi-Fi login page, and to use a VPN on public networks when you can.

## An analogy

The reception desk at a gym. You are already inside the building, but you cannot reach the machines until you show your card or sign the waiver at the counter.

## Keep in mind

- Common on airport, hotel and café Wi-Fi.
- You are on the network but cut off from the internet until you log in or accept.
- Devices detect it by loading a test page and open the login window automatically.
- Fake portals are an easy phishing trick; do not reuse real passwords there.

## Go deeper

- [Captive portal on Wikipedia](https://en.wikipedia.org/wiki/Captive_portal)
- [RFC 8910, Captive-Portal Identification in DHCP and Router Advertisements](https://www.rfc-editor.org/rfc/rfc8910)

## Related terms

- [Website](https://tidbit.legios.com.ar/website/): A set of web pages under one address, stored on a server and opened in a browser.
- [Wi-Fi](https://tidbit.legios.com.ar/wi-fi/): Networking over radio waves: the internet without the cable, within a few rooms.
- [Internet](https://tidbit.legios.com.ar/internet/): A worldwide network of networks that lets any connected device reach any other.
- [Laptop](https://tidbit.legios.com.ar/laptop/): A whole computer folded into one portable case that runs on a battery.
- [Apple](https://tidbit.legios.com.ar/apple/): The company that sells the iPhone and the Mac, plus the services that run on them.
- [Google](https://tidbit.legios.com.ar/google/): The search company that gives most products away and makes its money on ads.
- [Microsoft](https://tidbit.legios.com.ar/microsoft/): The company of Windows and Office, now just as much a cloud company with Azure.
- [MAC address](https://tidbit.legios.com.ar/mac-address/): The built-in name of a network card, used to deliver data inside a local network.