Captive-Portal Identification in DHCP and Router Advertisements (RAs)
RFC 8910

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Internet Engineering Task Force (IETF)                         W. Kumari
Request for Comments: 8910                                        Google
Obsoletes: 7710                                                 E. Kline
Updates: 3679                                                       Loon
Category: Standards Track                                 September 2020
ISSN: 2070-1721

 Captive-Portal Identification in DHCP and Router Advertisements (RAs)

Abstract

   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 user can do
   until the user has satisfied the captive portal conditions.

   This document describes a DHCPv4 and DHCPv6 option and a Router
   Advertisement (RA) option to inform clients that they are behind some
   sort of captive portal enforcement device, and that they will need to
   satisfy the Captive Portal conditions 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 one component of a
   standardized approach for hosts to interact with such portals.  While
   this document defines how the network operator may convey the captive
   portal API endpoint to hosts, the specific methods of satisfying and
   interacting with the captive portal are out of scope of this
   document.

   This document replaces RFC 7710, which used DHCP code point 160.  Due
   to a conflict, this document specifies 114.  Consequently, this
   document also updates RFC 3679.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8910.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
     1.1.  Requirements Notation
   2.  The Captive-Portal Option
     2.1.  IPv4 DHCP Option
     2.2.  IPv6 DHCP Option
     2.3.  The Captive-Portal IPv6 RA Option
   3.  Precedence of API URIs
   4.  IANA Considerations
     4.1.  Captive Portal Unrestricted Identifier
     4.2.  BOOTP Vendor Extensions and DHCP Options Code Change
     4.3.  Update DHCPv6 and IPv6 ND Options Registries
   5.  Security Considerations
   6.  References
     6.1.  Normative References
     6.2.  Informative References
   Appendix A.  Changes from RFC 7710
   Appendix B.  Observations from IETF 106 Network Experiment
   Acknowledgements
   Authors' Addresses

1.  Introduction

   In many environments, users need to connect to a captive portal
   device and agree to an Acceptable Use Policy (AUP) and/or provide
   billing information before they can access the Internet.  Regardless
   of how that mechanism operates, this document provides functionality
   to allow the client to know when it is behind a captive portal and
   how to contact it.

   In order to present users with the payment or AUP pages, a captive
   portal enforcement device presently has to intercept the user's
   connections and redirect the user to a captive portal server, using
   methods that are very similar to man-in-the-middle (MITM) attacks.
   As increasing focus is placed on security, and end nodes adopt a more
   secure stance, these interception techniques will become less
   effective and/or more intrusive.

   This document describes a DHCPv4 [RFC2131] and DHCPv6 [RFC8415]
   option (Captive-Portal) and an IPv6 Router Advertisement (RA)
   [RFC4861] option that informs clients that they are behind a captive
   portal enforcement device and the API endpoint that the host can
   contact for more information.

   This document replaces RFC 7710 [RFC7710], which used DHCP code point
   160.  Due to a conflict, this document specifies 114.  Consequently,
   this document also updates [RFC3679].

1.1.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",