< draft-wkumari-dhc-capport-01.txt   draft-wkumari-dhc-capport-02.txt >
DHC W. Kumari Network Working Group W. Kumari
Internet-Draft Google Internet-Draft Google
Intended status: Informational O. Gudmundsson Intended status: Informational O. Gudmundsson
Expires: July 27, 2014 Shinkuro Inc. Expires: October 18, 2014 Shinkuro Inc.
P. Ebersman P. Ebersman
Infoblox Infoblox
S. Sheng S. Sheng
ICANN ICANN
January 23, 2014 April 16, 2014
Captive-Portal identification in DHCP Captive-Portal identification in DHCP / RA
draft-wkumari-dhc-capport-01 draft-wkumari-dhc-capport-02
Abstract Abstract
In many environments (such as hotels, coffee shops and other In many environments (such as hotels, coffee shops and other
establishments that offer Internet service to customers), it is establishments that offer Internet service to customers), it is
common to start new connections in a captive portal mode, i.e. highly common to start new connections in a captive portal mode, i.e. highly
restrict what the customer can do until the customer has accepted restrict what the customer can do until the customer has accepted
terms of service, provided payment information or authenticated. terms of service, provided payment information or authenticated.
This document describes a DHCP option to inform clients that they are This document describes a DHCP option (and an RA extension) to inform
behind some sort of captive portal device, and that they will need to clients that they are behind some sort of captive portal device, and
authenticate to get Internet Access. that they will need to authenticate to get Internet Access.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 27, 2014. This Internet-Draft will expire on October 18, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3 1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. DNS Redirection . . . . . . . . . . . . . . . . . . . . . 3 2.1. DNS Redirection . . . . . . . . . . . . . . . . . . . . . 3
2.2. HTTP Redirection . . . . . . . . . . . . . . . . . . . . 4 2.2. HTTP Redirection . . . . . . . . . . . . . . . . . . . . 4
2.3. IP Hijacking . . . . . . . . . . . . . . . . . . . . . . 4 2.3. IP Hijacking . . . . . . . . . . . . . . . . . . . . . . 4
3. The Captive-Portal DHCP Option . . . . . . . . . . . . . . . 4 3. The Captive-Portal DHCP Option . . . . . . . . . . . . . . . 4
4. Use of the Captive-Portal Option . . . . . . . . . . . . . . 5 4. The Captive-Portal RA Option . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5. Use of the Captive-Portal Option . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . 8 9.1. Normative References . . . . . . . . . . . . . . . . . . 9
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 8 9.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
In many environments (coffee shops and hotels), users need to connect In many environments (coffee shops and hotels), users need to connect
to a captive portal device and agree to an acceptable use policy or to a captive portal device and agree to an acceptable use policy or
provide billing information before they can access the Internet. provide billing information before they can access the Internet.
In order to present the user with the captive portal web page, many In order to present the user with the captive portal web page, many
devices perform DNS and / or HTTP and / or IP hijacks. As well as devices perform DNS and / or HTTP and / or IP hijacks. As well as
being kludgy hacks, these techniques looks very similar to attacks being kludgy hacks, these techniques looks very similar to attacks
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contain an IPv6 address (to account for IPv4 only or IPv6 only contain an IPv6 address (to account for IPv4 only or IPv6 only
capable devices - not everyting is dual stack!) capable devices - not everyting is dual stack!)
[ED NOTE: Using an address literal is less than ideal, but better [ED NOTE: Using an address literal is less than ideal, but better
than the alternatives. Recommending a DNS name means that the CP than the alternatives. Recommending a DNS name means that the CP
would need to allow DNS from unauthenticated clients (as we don't would need to allow DNS from unauthenticated clients (as we don't
want to force users to use the CP's provided DNS) and some folk would want to force users to use the CP's provided DNS) and some folk would
use this to DNS Tunnel out. This would make the CP admin block use this to DNS Tunnel out. This would make the CP admin block
external recursives).] external recursives).]
4. Use of the Captive-Portal Option 4. The Captive-Portal RA Option
[ Ed: I'm far from an RA expert, but it was suggested that we shold
advertize this via RA as well as DHCP. I think there are only 8 bits
for Type, is it worth burning an option code on this? I have also
specified that the option length should padded to multiples of 8 byte
to better align with the examples I've seen (and I'm on a plane so
cannot easily search for more!) Is this required / preferred, or is
smaller RAs better? ]
This section describes the Captive-Portal Router Advertisement
option.
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 | Length | URI .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ .
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Captive-Portal RA Option Format
Type TBA3
Length 8-bit unsigned integer. The length of the option (including
the Type and Length fields) in units of 8 bytes.
URI The URI of the authentication page that the user should connect
to. This should be padded with NULL (0x0) to make the total
option length (including the Type and Length fields) a mutliple of
8 bytes.
5. Use of the Captive-Portal Option
[ED NOTE: This section is, and probably will remain, fairly hand [ED NOTE: This section is, and probably will remain, fairly hand
wavy. This option provides notice to the OS / User applications that wavy. This option provides notice to the OS / User applications that
there is a CP, but I think that the UI / etc is best designed / there is a CP, but I think that the UI / etc is best designed /
handled by the Operating System vendors / Application developers. ] handled by the Operating System vendors / Application developers. ]
The purpose of the Captive-Portal DHCP Option is to inform the
operating system and applications that they are behind a captive The purpose of the Captive-Portal Option is to inform the operating
portal type device and will need to authenticate before getting system and applications that they are behind a captive portal type
network access (and how to reach the authentication page). device and will need to authenticate before getting network access
(and how to reach the authentication page).
The Captive-Portal Option is defined for IPv6 RAs and IPv6 DHCP and
IPv4 DHCP. The URIs in these SHOULD all be the same, but if they are
not, the precedence is as follows:
1. IPv6 DHCP (most preferred)
2. IPv4 DHCP
3. IPv6 RA (least preferred)
This preference was chosen because an IPv6 capable client machine
will first get an IP address (and possibly the Captive-Portal option)
via RA, and will then get additional information via DHCP v6. The
client is not fully configured until it has completed the DHCP step,
and so this is "newer" information. The DHCP v4 preference is in the
middle, because it is likely that this will be delpoyed first on many
captive portals. Once IPv6 is deployed, we don't want legacy
(forgotten!) configuration to override the "newer" configuration
information. [Ed: This ordering is somewhat arbritary, as is the
justification, but there should be *some* standard and this seemed as
good as any! ]
The exact method that the interaction with the user occurs is device The exact method that the interaction with the user occurs is device
/ operating system / application dependent. The below is simply one / operating system / application dependent. The below is simply one
option. option.
When the device receives a DHCP response with the Captive-Portal When the device receives a DHCP response with the Captive-Portal
Option it SHOULD: Option it SHOULD:
1. Not initiate new IP connections until the CP has been satisfied. 1. Not initiate new IP connections until the CP has been satisfied.
[TODO(Someone): Existing connections should be quiesced. This Existing connections should be quiesced. This will happen more
will happen more often than some expect -- you buy 1h of Internet often than some expect -- you buy 1h of Internet at a cafe and
at a cafe and stay there for 3h -- this will "interrupt" you a stay there for 3h -- this will "interrupt" you a few times).
few times).]
2. Present a dialog box to the user informing that they are behind a 2. Present a dialog box to the user informing that they are behind a
captive portal and ask if they wish to proceed. captive portal and ask if they wish to proceed.
3. If the user elects to proceed, the device should initiate a 3. If the user elects to proceed, the device should initiate a
connection to the captive portal login page using a web browser connection to the captive portal login page using a web browser
configured with a separate cookie store. Some captive portals configured with a separate cookie store. Some captive portals
send the user a cookie when they authenticate (so that the user send the user a cookie when they authenticate (so that the user
can re-authenticate more easily in the future - the browser can re-authenticate more easily in the future - the browser
should keep these CP cookies separate from other cookies. should keep these CP cookies separate from other cookies.
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4. Once the user has authenticated (how does it know? HTTP 4. Once the user has authenticated (how does it know? HTTP
response?! Probe (ugh?)) normal IP connectivity should resume. response?! Probe (ugh?)) normal IP connectivity should resume.
5. The device should (using an OS dependent method) expose to the 5. The device should (using an OS dependent method) expose to the
user / user applications that they have connected though a user / user applications that they have connected though a
captive portal (for example by creating a file in /proc/net/ captive portal (for example by creating a file in /proc/net/
containing the interface and captive portal URI). This should containing the interface and captive portal URI). This should
continue until the network changes, or a new DHCP message without continue until the network changes, or a new DHCP message without
the CP is received. the CP is received.
5. IANA Considerations 6. IANA Considerations
[ This section stolen from draft-ietf-dhc-access-network-identifier.
:-) ]
This document defines DHCPv4 Captive-Portal option which requires This document defines DHCPv4 Captive-Portal option which requires
assignment of DHCPv4 option code TBA1 assigned from "Bootp and DHCP assignment of DHCPv4 option code TBA1 assigned from "Bootp and DHCP
options" registry (http://www.iana.org/assignments/ bootp-dhcp- options" registry (http://www.iana.org/assignments/ bootp-dhcp-
parameters/bootp-dhcp-parameters.xml), as specified in [RFC2939]. parameters/bootp-dhcp-parameters.xml), as specified in [RFC2939].
The IANA is requested to assign an option codes for the DHCPv6 The IANA is requested to also assign an option codes for the DHCPv6
Captive-Portal (TBA2) option from the "DHCPv6 and DHCPv6 options" Captive-Portal (TBA2) option from the "DHCPv6 and DHCPv6 options"
registry (http:// www.iana.org/assignments/dhcpv6-parameters/ registry (http:// www.iana.org/assignments/dhcpv6-parameters/
dhcpv6-parameters.xml). dhcpv6-parameters.xml).
6. Security Considerations The IANA is also requested at assign an IPv6 RA Type code (TBA3) from
the [TODO] registry. Thanks IANA!
7. Security Considerations
An attacker with the ability to inject DHCP messages could include An attacker with the ability to inject DHCP messages could include
this option and so force users to contact him. As an attacker with this option and so force users to contact him. As an attacker with
this capability could simply list himself as the default gateway (and this capability could simply list himself as the default gateway (and
so see all the victim's traffic), we do not think this gives them so see all the victim's traffic), we do not think this gives them
significantly more capabilities. Fake DHCP servers are currently a significantly more capabilities. Fake DHCP servers / fake RAs are
security concern - this doesn't make them any better or worse. currently a security concern - this doesn't make them any better or
worse.
Devices and systems that automatically connect to open network could Devices and systems that automatically connect to open network could
potentially be tracked using the techniques described in this potentially be tracked using the techniques described in this
document (forcing the user to continually authenticate, or exposing document (forcing the user to continually authenticate, or exposing
their browser fingerprint), but similar tracking could already be their browser fingerprint), but similar tracking could already be
performed with the standard captive portal mechanisms, so this performed with the standard captive portal mechanisms, so this
doesn't seem to give the attackers more capabilities. doesn't seem to give the attackers more capabilities.
By simplifying the interaction with the captive portal systems, and By simplifying the interaction with the captive portal systems, and
doing away with the need for interception, we think that users will doing away with the need for interception, we think that users will
be less likely to disable useful security safeguards like DNSSEC be less likely to disable useful security safeguards like DNSSEC
validation, VPNs, etc. validation, VPNs, etc.
7. Acknowledgements 8. Acknowledgements
The primary author has discussed this idea with a number of folk, and The primary author has discussed this idea with a number of folk, and
asked them to assist by becoming co-authors. Unfortunately he has asked them to assist by becoming co-authors. Unfortunately he has
forgotten who many of them were; if you were one of them, I forgotten who many of them were; if you were one of them, I
apologize. apologize.
Thanks to Vint Cerf for the initial idea / asking me to write this. Thanks to Vint Cerf for the initial idea / asking me to write this.
Thanks to Wes George for supplying the v6 text. Thanks to Wes George for supplying the v6 text.
8. References 9. References
8.1. Normative References 9.1. Normative References
[IANA.AS_Numbers] [IANA.AS_Numbers]
IANA, "Autonomous System (AS) Numbers", IANA, "Autonomous System (AS) Numbers",
<http://www.iana.org/assignments/as-numbers>. <http://www.iana.org/assignments/as-numbers>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
8.2. Informative References 9.2. Informative References
[I-D.ietf-sidr-iana-objects] [I-D.ietf-sidr-iana-objects]
Manderson, T., Vegoda, L., and S. Kent, "RPKI Objects Manderson, T., Vegoda, L., and S. Kent, "RPKI Objects
issued by IANA", draft-ietf-sidr-iana-objects-03 (work in issued by IANA", draft-ietf-sidr-iana-objects-03 (work in
progress), May 2011. progress), May 2011.
Appendix A. Changes / Author Notes. Appendix A. Changes / Author Notes.
[RFC Editor: Please remove this section before publication ] [RFC Editor: Please remove this section before publication ]
From -01 to 02:
o Added the IPv6 RA stuff.
From -00 to -01: From -00 to -01:
o Many nits and editorial changes. o Many nits and editorial changes.
o Whole bunch of extra text and review from Wes George on v6. o Whole bunch of extra text and review from Wes George on v6.
From initial to -00. From initial to -00.
o Nothing changed in the template! o Nothing changed in the template!
 End of changes. 19 change blocks. 
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