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template                                                         D. Bird
Internet-Draft                                                 W. Kumari
Intended status: Informational                                    Google
Expires: October 4, 2017                                   April 2, 2017


                      Captive Portal ICMP Messages
                 draft-wkumari-capport-icmp-unreach-02

Abstract

   This document defines a new ICMP Type for Captive Portal Messages.
   The ICMP Type will only be known to clients supporting this
   specification and provides both generic and flow 5-tuple specific
   notifications from the Captive Portal NAS.

   Further, This document defines a multi-part ICMP extension to ICMP
   Destination Unreachable messages to signal, not only that the packet
   was dropped, but that it was dropped due to an Access Policy
   requiring Captive Portal interaction.  Legacy clients will only be
   processing the ICMP Destination Unreachable.

   [ Editor note: The IETF is currently discussing improvements in
   captive portal interactions and user experience improvements.  See:
   https://www.ietf.org/mailman/listinfo/captive-portals ]

   [RFC Editor: Please remove this before publication.  This document is
   being stored in github at https://github.com/wlanmac/draft-wkumari-
   capport-icmp-unreach . Authors gratefully accept pull requests, and
   keep the latest (edit buffer) versions there, so commenters can
   follow along at home.]

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 4, 2017.



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Copyright Notice

   Copyright (c) 2017 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
   (http://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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements notation . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Captive Portal ICMP . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Session-ID  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Flags . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Validity  . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.4.  Delay . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.5.  Policy Class  . . . . . . . . . . . . . . . . . . . . . .   5
     2.6.  Message Code/C-Type . . . . . . . . . . . . . . . . . . .   6
     2.7.  Message Type  . . . . . . . . . . . . . . . . . . . . . .   6
     2.8.  Extension Object  . . . . . . . . . . . . . . . . . . . .   7
   3.  Captive Portal URL Formatting . . . . . . . . . . . . . . . .   8
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Appendix A.  Changes / Author Notes.  . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Captive Portals work by blocking (or redirecting) communications
   outside of a "walled garden" until the user has either authenticated,
   acknowledged an Acceptable Use Policy (AUP), or otherwise satisfied
   the requirements of the Captive Portal.  Depending on the captive
   portal implementation, connections other than HTTP will either
   timeout (silently packets dropped) or meet with a different,




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   inaccurate, error condition (like a TCP reset, for TCP connections,
   or ICMP Destination Unreachable with existing codes).

   A current option for captive portal networks is to reject traffic not
   in the walled garden by returning the Destination Unreachable either
   Host or Network Administratively Prohibited.  However, these codes
   are typically permanent policies and do not specifically indicate a
   captive portal is in use.

   This document defines a new ICMP Type for Captive Portal.  The
   Captive Portal ICMP Type can be used to send flow 5-tuple specific or
   general notifications to user devices.  As a new ICMP type, it is
   expected to be ignored by legacy devices.

   This document also defines an Extension Object that can be appended
   to selected multi-part ICMP messages to inform the user device that
   they are behind a captive portal, in addition to the underlying ICMP
   information.  Devices able to understand the extension get extra
   information about the captive portal access policy, whereas legacy
   devices just understand the underlying ICMP message.

   The Captive Portal and Destination Unreachable types provide the
   Captive Portal NAS options in terms of what notifications legacy
   devices can and should understand.

   The Captive Portal ICMP Messages only provide notification.  They do
   not provide any configuration.  For that, we use [RFC7710] and the
   Captive Portal URI it provides.

1.1.  Requirements notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

1.2.  Terminology

   Capport ICMP device  Device or operating system compliant to this
      specification.

   CP-NAS  Network Access Server implementing Captive Portal
      enforcement.

   Legacy device  Device or operating system not compliant to this
      specification.






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2.  Captive Portal ICMP

   Captive Portal ICMP messages come in two flavors.  Messages can be
   sent using the Captive Portal ICMP Type or they can be sent as an
   ICMP Extension to an existing ICMP Type, such as Destination
   Unreachable.  Data is encoded into the packet slightly differently in
   each case, however, the field formats remain consistent.  All fields
   are in network byte order.

   Capport ICMP devices MUST support [RFC7710].

2.1.  Session-ID

   An unsigned short session identifier that groups ICMP messages.  ICMP
   messages containing the same value MUST be assumed to be part of the
   same access policy.  Any change in this value between ICMP messages
   from the same source IP address MUST be considered by the client to
   mean a change in access policy has occurred and previous
   notifications are no longer valid.

              0                   1
              0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             |          Session-ID           |
             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

2.2.  Flags

   In Captive Portal ICMP Messages, a flags field contains bit flags for
   optional payload data fields.  All data fields are unsigned 32bit
   integers.

   Bit flags and their (optional) respective data fields:

              0 1 2 3 4 5 6 7
             +-+-+-+-+-+-+-+-+
             |V|D|P|   zero  |
             +-+-+-+-+-+-+-+-+

   V - 1 bit  Validity

   D - 1 bit  Delay

   P - 1 bit  Policy Class

   Optional fields included in flags appear in the ICMP payload in the
   same order as the respective bits.




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           0                   1                   2                   3
           0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                        Validity (optional)                    |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                         Delay (optional)                      |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                     Policy-Class (optional)                   |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

2.3.  Validity

   The Validity time, in seconds, that this result should be considered
   valid and the OS SHOULD not attempt to access the same resource in
   the meantime.  During the Validity time, the NAS MAY chose to
   silently drop the packets of the same flow 5-tuple to selectively
   cause legacy clients to time-out connections.

           0                   1                   2                   3
           0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                 Validity (seconds as uint32)                  |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

2.4.  Delay

   The Delay time, in seconds, is the time in future when this result
   should be considered valid.  This is used to give advanced notice
   that a change in access policy is about to happen.

           0                   1                   2                   3
           0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                   Delay (seconds as uint32)                   |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

2.5.  Policy Class

   The Policy Class is an unsigned integer that provides a "hint" to the
   captive portal.  When a client is specifically responding to a
   Captive Portal ICMP message and is launching a browser, the Policy
   Class is given to the portal as a reason for the visitor to visit the
   portal.








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           0                   1                   2                   3
           0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                      Policy Class (uint32)                    |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

2.6.  Message Code/C-Type

   Captive Portal Message Code and C-Types:

   0  General Change of Authorization (change in policy)

   1  Packet/flow Error (dropped)

   2  Packet/flow Overflow (dropped)

   3  Packet/flow Warning (not dropped)

2.7.  Message Type

   The Captive Portal ICMP Type message is specifically for Capport ICMP
   Compliant devices.  It is expected that Legacy devices will ignore
   such messages.

           0                   1                   2                   3
           0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |      Type     |      Code     |          Checksum             |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |V|D|P|  zero   |     Length    |          Session-ID           |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |      Internet Header + leading octets of original datagram    |
          |                                                               |
          |                           //                                  |
          |                                                               |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                        Validity (optional)                    |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                         Delay (optional)                      |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                     Policy-Class (optional)                   |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   As shown in the figure above, the Captive Portal Flags and Session-ID
   and part of the ICMP header.  The optional fields are in the ICMP
   payload, past the (optional) original datagram headers of a length
   defined by Length.




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   Length  Number of 4 byte words of original datagram.

2.8.  Extension Object

   This document defines an extension object that can be appended to
   selected multi-part ICMP messages ([RFC4884]).  This extension
   permits the CP-NAS to inform Capport ICMP Compliant devices that
   their connection has been blocked due to an Access Policy requiring
   interaction with the Captive Portal.

   The Captive Portal Extension Object can be appended to the ICMP
   Destination Unreachable messages.  When Legacy devices receive such
   messages, they will only understand the Destination Unreachable,
   ignoring the extensions.

   When used in an Extension Object, the Captive Portal ICMP data fields
   are packed into an extension structure as shown below.

           0                   1                   2                   3
           0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |V|D|P|       Reserved          |         Session-ID            |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                        Validity (optional)                    |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                         Delay (optional)                      |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                     Policy-Class (optional)                   |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The following figure depicts the Destination Unreachable message with
   Captive Portal Extension.  It must be preceded by an ICMP Extension
   Structure Header and an ICMP Object Header.  Both are defined in
   [RFC4884].

















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           0                   1                   2                   3
           0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |     Type      |      Code     |          Checksum             |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |     unused    |    Length-A   |         Next-Hop MTU*         |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |      Internet Header + leading octets of original datagram    |
          |                                                               |
          |                           //                                  |
          |                                                               |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |Version|      (Reserved)       |           Checksum            |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |             Length-B          |   Class-Num   |   C-Type      |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |V|D|P|       Reserved          |         Session-ID            |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                        Validity (optional)                    |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                         Delay (optional)                      |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          |                     Policy-Class (optional)                   |
          +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type  Set to 3 for Destination Unreachable.

   Code  Can be any value Code value for Type.

   Length-A  Length, in 4 byte words, of original datagram.

   Version  Set to version 2, per RFC 4884.

   Length-B  Length of extension.

   Class-Num  Set to Captive Portal Class-Num.

   C-Type  See section 2.6.

3.  Captive Portal URL Formatting

   The Session-ID and Policy Class is used along with the RFC 7710 URI
   received from DHCP or IPv6 RA to send the user to the captive portal.

           RFC_7710_URI . SEP .
                 'icmp_session=' . SESSION_ID . '&' .
                 'policy_class=' . [POLICY_CLASS[,POLICY_CLASS]]




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   RFC_7710_URI  The URI received from DHCP or IPv6 RA per RFC 7710.

   SEP  If the RFC_7710_URI contains a '?', then SEP equals ampersand,
      otherwise a question mark.

   SESSION_ID  The Session-ID value in integer format.

   POLICY_CLASS  Zero or more Policy Class values gathers for the same
      Session-ID leading to the user notification..

   Examples:

        https://wifi.domain.com/portal?icmp_session=10&policy_class=100
        https://my.domain.com/?do=login&icmp_session=10&policy_class=100,20

4.  IANA Considerations

   The IANA is requested to assign a Captive Portal ICMP Message Type,
   as well as Code values defined in section 2.6..

   The IANA is also requested to assign a Class-Num identifier for the
   Captive Portal Extension Object from the ICMP Extension Object
   Classes and Class Sub-types registry.

   The IANA is also requested to form and administer the corresponding
   class sub-type (C-Type) space per section 2.6.

5.  Security Considerations

   This method simply annotates existing ICMP Destination Unreachable
   messages to inform users why their connection was blocked.  This
   technique can be used to inform captive portal detection probe
   software that there is a captive portal present (and potentially to
   connect to the URL handed out using draft-wkumari-dhc-capport.  We
   anticipate that there will be a new solution devised (such as a well
   known URL / URI on captive portals) to allow the user / captive
   portal probe to do something more useful with this information.

6.  Acknowledgements

   The authors wish to thank the authors of RFC4950 (especially Ron
   Bonica ) - I stole much of his text when writing the extension
   definition.








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7.  References

7.1.  Normative References

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, DOI 10.17487/RFC0792, September 1981,
              <http://www.rfc-editor.org/info/rfc792>.

   [RFC1122]  Braden, R., Ed., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122,
              DOI 10.17487/RFC1122, October 1989,
              <http://www.rfc-editor.org/info/rfc1122>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC4884]  Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
              "Extended ICMP to Support Multi-Part Messages", RFC 4884,
              DOI 10.17487/RFC4884, April 2007,
              <http://www.rfc-editor.org/info/rfc4884>.

   [RFC7710]  Kumari, W., Gudmundsson, O., Ebersman, P., and S. Sheng,
              "Captive-Portal Identification Using DHCP or Router
              Advertisements (RAs)", RFC 7710, DOI 10.17487/RFC7710,
              December 2015, <http://www.rfc-editor.org/info/rfc7710>.

7.2.  Informative References

   [I-D.ietf-sidr-iana-objects]
              Manderson, T., Vegoda, L., and S. Kent, "RPKI Objects
              issued by IANA", draft-ietf-sidr-iana-objects-03 (work in
              progress), May 2011.

Appendix A.  Changes / Author Notes.

   [RFC Editor: Please remove this section before publication ]

   From -01 to 02.

   o  Added a new ICMP Type, redefined message payload and flags, and
      introduces Codes/C-Types.



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   From -00 to 01.

   o  Changed the Captive Portal URL to a URI, and specificed that this
      can ONLY contain a path element, which is appended to
      http://<gateway_ip>.  This is to prevent hijacking connections to
      other addresses.

   o  Then removed the entire URL / URI scheme entirely.

   From -genesis to -00.

   o  Initial text.

Authors' Addresses

   David Bird
   Google
   1600 Amphitheatre Parkway
   Mountain View, CA  94043
   US

   Email: dbird@google.com


   Warren Kumari
   Google
   1600 Amphitheatre Parkway
   Mountain View, CA  94043
   US

   Email: warren@kumari.net




















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