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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-01
Abstract
This document defines a multi-part ICMP extension to ICMP Destination
Unreachable messages to signal that a user 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
provisions of BCP 78 and BCP 79.
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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.
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This document is subject to BCP 78 and the IETF Trust's Legal
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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 . . . . . . . . . . . . . . . . . . . 4
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 -
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wkumari-dhc-capport provides information from a DHCP server (and so
doesn't need any changes to deployed CPs), and provides information
*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.
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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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).
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,
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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.
[ 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
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
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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 sometyhing more useful with this information.
5. Acknowledgements
The authors wish to thank the Yaron Sheffer and 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.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC
3986, January 2005.
[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 -00 to 01.
o Changed the Captive Portal URL to a URI, and specificed that this
can ONLY contain a path element, which is appened to
http://<gateway_ip>. This is to prevent hijacking connections to
other addresses.
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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: [email protected]
Warren Kumari
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: [email protected]
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