1. Initial state:
Wi-Fi enabled, but not connected to any network; ethernet is unplugged.
$ nmcli general
STATE CONNECTIVITY WIFI-HW WIFI WWAN-HW WWAN
disconnected none enabled enabled enabled enabled
2. Connect to a SSID that has captive portal:
$ nmcli general
STATE CONNECTIVITY WIFI-HW WIFI WWAN-HW WWAN
connected full enabled enabled enabled enabled
This means network-manager has put the state to connected and emits a signal of full connectivity, which makes other applications "think" the device is online with full access to the Internet.
Just did some testing with up-to-date 16.04 LTS:
1. Initial state:
Wi-Fi enabled, but not connected to any network; ethernet is unplugged.
$ nmcli general
STATE CONNECTIVITY WIFI-HW WIFI WWAN-HW WWAN
disconnected none enabled enabled enabled enabled
2. Connect to a SSID that has captive portal:
$ nmcli general
STATE CONNECTIVITY WIFI-HW WIFI WWAN-HW WWAN
connected full enabled enabled enabled enabled
This means network-manager has put the state to connected and emits a signal of full connectivity, which makes other applications "think" the device is online with full access to the Internet.