In many environments offering short-term or temporary Internet access (such as
coffee shops), it is common to start new connections in a captive-portal mode. This
highly restricts what the customer can do until the customer has authenticated.
This document describes a DHCP option (and a Router Advertisement (RA) extension)
to inform clients that they are behind some sort of captive-portal device and that
they will need to authenticate to get Internet access. It is not a full solution to
address all of the issues that clients may have with captive portals; it is
designed to be used in larger solutions. The method of authenticating to and
interacting with the captive portal is out of scope for this document.