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
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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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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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