< draft-wkumari-dhc-capport-00.txt   draft-wkumari-dhc-capport-01.txt >
DHC W. Kumari DHC W. Kumari
Internet-Draft Google Internet-Draft Google
Intended status: Informational O. Gudmundsson Intended status: Informational O. Gudmundsson
Expires: July 17, 2014 Shinkuro Inc. Expires: July 27, 2014 Shinkuro Inc.
P. Ebersman P. Ebersman
Infoblox Infoblox
S. Sheng S. Sheng
ICANN ICANN
January 13, 2014 January 23, 2014
Captive-Portal identification in DHCP Captive-Portal identification in DHCP
draft-wkumari-dhc-capport-00 draft-wkumari-dhc-capport-01
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 common establishments that offer Internet service to customers), it is
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 to inform clients that they are
behind some sort of captive portal device, and that they will need to behind some sort of captive portal device, and that they will need to
authenticate to get Internet Access. 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
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 17, 2014. This Internet-Draft will expire on July 27, 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
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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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. Use of the Captive-Portal Option . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7 8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 7 Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
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
that DNSSEC and TLS protect against. that DNSSEC and TLS protect against.
This document describes a DHCP option (Captive-Portal) that informs This document describes a DHCP option (Captive-Portal) that informs
DHCP clients that they are behind a captive portal device, and how to DHCP clients that they are behind a captive portal device, and how to
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1.1. Requirements notation 1.1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Background 2. Background
Many Internet Service Providers (ISPs) that offer public Internet Many Internet Service Providers (ISPs) that offer public Internet
access require theuser to first accept an Acceptable Use Policy (AUP) access require the user to first accept an Acceptable Use Policy
and / or provides billing information (such as their last name and / (AUP) and / or provides billing information (such as their last name
or room number in a hotel, credit card information, etc) through a and / or room number in a hotel, credit card information, etc)
web interface. through a web interface.
In order to meet this requirement, some ISPs implement a captive In order to meet this requirement, some ISPs implement a captive
portal (CP) - a system that intercepts user requests and redirects portal (CP) - a system that intercepts user requests and redirects
them to an interstitial login page. them to an interstitial login page.
Captive portals intercept and redirects user requests in a number of Captive portals intercept and redirects user requests in a number of
ways, including: ways, including:
o DNS Redirection o DNS Redirection
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the user has authenticated to the captive portal, the CP responds to the user has authenticated to the captive portal, the CP responds to
all DNS requests listing the address of its web portal. Once the all DNS requests listing the address of its web portal. Once the
user has authenticated the CP returns the "correct" addresses. user has authenticated the CP returns the "correct" addresses.
This technique has many shortcomings. It fails if the client is This technique has many shortcomings. It fails if the client is
performing DNSSEC validation, or if the client already has the DNS performing DNSSEC validation, or if the client already has the DNS
information cached. information cached.
2.2. HTTP Redirection 2.2. HTTP Redirection
In this implmentation, the CP acts like a transparent HTTP proxy, but In this implementation, the CP acts like a transparent HTTP proxy;
when it sees an HTTP request from an unauthenticated client it but when it sees an HTTP request from an unauthenticated client, it
intercepts the request and responds with an HTTP status code 302 to intercepts the request and responds with an HTTP status code 302 to
redirect the client to the Captive Portal Login. redirect the client to the Captive Portal Login.
The issues with this technique include: The issues with this technique include:
o It fails if the user is only using HTTPS o It fails if the user is only using HTTPS
o It exposes various private user information, such as HTTP Cookies, o It exposes various private user information, such as HTTP Cookies,
etc. etc.
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whatever the user tried to access. whatever the user tried to access.
This technique has similar issues as the HTTP solution, but may also This technique has similar issues as the HTTP solution, but may also
break other protocols, and may expose more of the users private break other protocols, and may expose more of the users private
information, etc. information, etc.
3. The Captive-Portal DHCP Option 3. The Captive-Portal DHCP Option
The Captive Portal DHCP Option (TBA1) informs the DHCP client that it The Captive Portal DHCP Option (TBA1) informs the DHCP client that it
is behind a captive portal and provides the URI to access the is behind a captive portal and provides the URI to access the
authentication page. authentication page. This is primarily intended to improve the user
experiance; for the forseeable future captive portals will still need
to implement the interception techniques to serve legacy clinets.
The format of the DHCPv4 Captive-Portal DHCP option is shown below. This draft is not intended to provide guidance on how to implement a
captive portal. As such, it assumes that the captive portal on a
dual-stack or IPv6-only network is already capable of intercepting
IPv6 traffic. However, in order to support IPv6 with the proposed
DHCP option, there are some additional considerations. In a dual-
stack network, the network supports both IPv4 and IPv6 protocols
simultaneously, but can have a mix of IPv4-only, IPv6-only, and dual-
stack devices using the network, meaning that it may be necessary to
have parallel notifications via DHCPv4 and DHCPv6.
IPv4-only and dual-stack devices can technically both support
receiving the option via DHCPv4, but dual-stack implementations would
need to ensure that the correct action would be taken for both IPv4
and IPv6 traffic despite only receiving an option via IPv4. For
devices/networks that only speak IPv6, and to avoid this dependency
on the implementation, a DHCPv6 option is necessary.
[ED NOTE:] This is complicated by the fact that not all devices
support DHCPv6, and thus it may be necessary to investigate other
methods to notify IPv6-only devices of a captive portal. Since this
option is only intended to help clients gracefully deal with networks
that have a captive portal, it may be acceptable to note that if a
client does not support DHCPv6, it simply won't be able to take
advantage of this optimization, but will otherwise function normally.
[/note]
The format of the DHCP Captive-Portal DHCP option is identical for
both DHCPv4 and DHCPv6 and is shown below.
Code Len Data Code Len Data
+------+------+------+------+------+-- --+-----+ +------+------+------+------+------+-- --+-----+
| code | len | URI ... | | code | len | URI ... |
+------+------+------+------+------+-- --+-----+ +------+------+------+------+------+-- --+-----+
o Code: The Captive-Portal DHCP Option (TBA1) o Code: The Captive-Portal DHCP Option (TBA1 for DHCPv4, TBA2 for
DHCPv6)
o Len: The length, in octets of the URI. o Len: The length, in octets of the URI.
o URI: The URI of the authentication page that the user should o URI: The URI of the authentication page that the user should
connect to. connect to.
The URI SHOULD be a URL with an IP-literal for the host portion (to The URI MUST be a URL with an IP-literal for the host portion (to
remove the need to allow DNS from unauthenticated clients). remove the need to allow DNS from unauthenticated clients). The
DHCPv4 URI MUST contain an IPv4 address, and the DHCPv6 URI MUST
contain an IPv6 address (to account for IPv4 only or IPv6 only
capable devices - not everyting is dual stack!)
[ED NOTE: Using an address literal is less than awesome, 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. 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
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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. 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 The purpose of the Captive-Portal DHCP Option is to inform the
operating system and applications that they are behind a captive operating system and applications that they are behind a captive
portal type device, and will need to authenticate before getting portal type device and will need to authenticate before getting
network access (and how to reach the authentication page). network access (and how to reach the authentication page).
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 placed on hold [TODO(Someone): Existing connections should be quiesced. This
(need better text). This will happen more often than some expect will happen more often than some expect -- you buy 1h of Internet
-- you buy 1h of Internet at a cafe and stay there for 3h -- this at a cafe and stay there for 3h -- this will "interrupt" you a
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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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 5. IANA Considerations
[ This section stolen from draft-ietf-dhc-access-network-identifier. [ 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 TBD1 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
Captive-Portal (TBA2) option from the "DHCPv6 and DHCPv6 options"
registry (http:// www.iana.org/assignments/dhcpv6-parameters/
dhcpv6-parameters.xml).
6. Security Considerations 6. 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 victims 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 are currently a
security concern - this doesn't make them any better or worse. 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.
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validation, VPNs, etc. validation, VPNs, etc.
7. Acknowledgements 7. 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.
8. References 8. References
8.1. Normative References 8.1. 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
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[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 -00 to -01. From -00 to -01:
o Many nits and editorial changes.
o Whole bunch of extra text and review from Wes George on v6.
From initial to -00.
o Nothing changed in the template! o Nothing changed in the template!
Authors' Addresses Authors' Addresses
Warren Kumari Warren Kumari
Google Google
1600 Amphitheatre Parkway 1600 Amphitheatre Parkway
Mountain View, CA 94043 Mountain View, CA 94043
US US
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