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.
RFC 7710-2015 history
2015RFC 7710-2015 Captive-Portal Identification Using DHCP or Router Advertisements (RAs)