Captive Portal ICMP Destination Unreachable
draft-wkumari-capport-icmp-unreach-00

template                                                         D. Bird
Internet-Draft                                                 W. Kumari
Intended status: Informational                                    Google
Expires: October 31, 2015                                 April 29, 2015

              Captive Portal ICMP Destination Unreachable
                 draft-wkumari-capport-icmp-unreach-00

Abstract

   This document defines a multi-part ICMP extension to signal that a
   user's device is behind a Captive Portal.

   [ 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/wkumari/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
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   This Internet-Draft will expire on October 31, 2015.

Copyright Notice

   Copyright (c) 2015 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

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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements notation . . . . . . . . . . . . . . . . . .   3
   2.  ICMP Dest Unreachable Captive Portal Object . . . . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Appendix A.  Changes / Author Notes.  . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Captive Portals work by blocking (or redirecting) communications
   outside of a "walled garden" until the user has authenticated and /
   or acknowledged an Acceptable Use Policy (AUP).  Depending on the
   captive portal implementation, connections other than HTTP will
   either timeout (packets dropped) or meet with a different,
   inaccurate, error condition (like a TCP reset or ICMP Destination
   Unreachable with existing codes).

   A current option for captive portal networks is to reject traffic not
   in the walled garden 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 an extension object that can be appended to
   selected multi-part ICMP messages to inform the user that they are
   behind a captive portal.  This informs the user after they have
   attempted an initial connection and is generated by the Captive
   Portal NAS itself.

   [ Editor note: This is complementary, but solves a different problem
   to: https://tools.ietf.org/html/draft-wkumari-dhc-capport-12 -
   wkumari-dhc-capport provides information from a DHCP server (and so
   doesn't need any changes to deployed CPs, and provides information

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   *before* the client attempts a connection.  It does not, however,
   have a way of noting that an existing connection has been
   interrupted.]

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].

2.  ICMP Dest Unreachable Captive Portal Object

   This document defines an extension object that can be appended to
   selected multi-part ICMP messages ([RFC4884]).  This extension
   permits Captive Portal (CP) NAS devices to inform user devices that
   their connection has been blocked by the Captive Portal NAS, and,
   optionally, how to contact the Captive Portal to satisfy it.

   The Dest Unreachable Captive Portal Object can be appended to the
   ICMP Destination Unreachable messages.  Figure 1 depicts the Dest
   Unreachable Captive Portal Object.  It must be preceded by an ICMP
   Extension Structure Header and an ICMP Object Header.  Both are
   defined in [RFC4884].

     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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |W|  Reserved   |         Validity (seconds)                    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Captive Portal URL                      ~
       ~                           (optional)                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   W  - 1 bit  Warning.  Indicates that the Validity refers to when the
      service will be interrupted.  Note that the "offending" traffic
      was forwarded, not dropped.

   Validity - 24 bits  Time, in seconds, that this result should be
      considered valid (and the OS should not attempt to access the same
      resource in the meantime).

   Captive Portal URL - Variable  The optional URL of the Captive
      Portal.  This allows Captive Portal detection software running on
      the user's device to locate and connect to the captive portal to
      improve the user experience.  The length of the URL is calculated
      from the ICMP Extension Object header Length minue the ICMP

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      Extension Object and Captive Portal Object header lengths, which
      is zero when no URL is provided.

   Editor note / questions.  We are trying to get some feedback on A:
   this general idea and B: this implementation.

      Some open questions.

   W bit or C-Type  We have currently specified a single bit (W) to
      indicate that the remaining lease time is running low, and the the
      connection will be interrupted sometime "soon".  We could,
      instead, use a differnt C-Type.  I think a bit is cleaner (and we
      have reserved 7 bits for future flags), but could be convinced
      (or, better yet, bribed) I'm wrong.  Or that the whole "warning"
      idea is a bad one...

   Legacy interaction  If we *do* return e.g ICMP Destination
      Unreachable, Communication Administratively Prohibited to a
      "legacy" (non-Dest Unreachable Captive Portal Object aware) client
      with the 'W' bit set, what happens?  In the testing I did, nothing
      bad seemed to happen, but I *could* see that some hosts may stop
      sending to that address, or...

   General concept  Is this idea useful?

3.  IANA Considerations

   The IANA is requested to assign a Class-Num identifier for the Dest
   Unreachable Captive Portal 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, as follows:

      Dest Unreachable Captive Portal Sub-types:

   0  Reserved.

   1  This message format.

   0x02-0xF6   Available for assignment

   0xF7-0xFF  Reserved for private use

   C-Type values are assignable on a first-come-first-serve (FCFS)
   basis.

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   [ Editor note: Currently we are not using the C-Type for anything,
   but I filled this in anyway.  Probably we would overload it at a
   version identifier type thing, but it could also allow further
   extension, for example, a pointer to a status page. ]

4.  Security Considerations

   The obvious security consideration is how to confirm that the
   received ICMP Message actually came from a Captive Portal, and was
   not generated from a passive observer on the network (to force the
   user to connect to a malicious device.).

5.  Acknowledgements

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

6.  References

6.1.  Normative References

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, September 1981.

   [RFC1122]  Braden, R., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122, October 1989.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4884]  Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
              "Extended ICMP to Support Multi-Part Messages", RFC 4884,
              April 2007.

6.2.  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 -genesis to -00.

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   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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