< draft-wkumari-dhc-capport-03.txt   draft-wkumari-dhc-capport-04.txt >
Network Working Group W. Kumari Network Working Group W. Kumari
Internet-Draft Google Internet-Draft Google
Intended status: Informational O. Gudmundsson Intended status: Informational O. Gudmundsson
Expires: December 3, 2014 Shinkuro Inc. Expires: January 5, 2015 Shinkuro Inc.
P. Ebersman P. Ebersman
Infoblox Comcast
S. Sheng S. Sheng
ICANN ICANN
June 1, 2014 July 4, 2014
Captive-Portal identification in DHCP / RA Captive-Portal identification in DHCP / RA
draft-wkumari-dhc-capport-03 draft-wkumari-dhc-capport-04
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 and / or
authenticated.
This document describes a DHCP option (and an RA extension) to inform This document describes a DHCP option (and an RA extension) to inform
clients that they are behind some sort of captive portal device, and clients that they are behind some sort of captive portal device, and
that they will need to 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.
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
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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 December 3, 2014. This Internet-Draft will expire on January 5, 2015.
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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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
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 . . . . . . . . . . . . . . . . . . . . . 4
2.2. HTTP Redirection . . . . . . . . . . . . . . . . . . . . 4 2.2. HTTP Redirection . . . . . . . . . . . . . . . . . . . . 4
2.3. IP Hijacking . . . . . . . . . . . . . . . . . . . . . . 4 2.3. IP Hijacking . . . . . . . . . . . . . . . . . . . . . . 5
3. The Captive-Portal DHCP Option . . . . . . . . . . . . . . . 4 3. The Captive-Portal DHCP Option . . . . . . . . . . . . . . . 5
4. The Captive-Portal RA Option . . . . . . . . . . . . . . . . 5 4. The Captive-Portal RA Option . . . . . . . . . . . . . . . . 6
5. Use of the Captive-Portal Option . . . . . . . . . . . . . . 6 5. Use of the Captive-Portal Option . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 8 9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . 8 9.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 8 Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
In many environments users need to connect to a captive portal device In many environments, users need to connect to a captive portal
and agree to an acceptable use policy or provide billing information device and agree to an acceptable use policy and / or provide billing
before they can access the Internet. 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. This makes the user experience that DNSSEC and TLS protect against, which makes the user experience
sub-optimal. sub-optimal.
This document describes a DHCP option (Captive-Portal) and IPv6 This document describes a DHCP option (Captive-Portal) and an IPv6
Router Advertisement (RA) extension that informs clients that they Router Advertisement (RA) extension that informs clients that they
are behind a captive portal device, and how to contact it. are behind a captive portal device, and how to contact it.
This document neither condones nor condemns captive portals; instead This document neither condones nor condemns captive portals; instead,
it recognises that they are here to stay, and attempts to improve the it recognises that they are here to stay, and attempts to improve the
user's experience. user experience.
The technique described in this document mainly improve the user
experience when first connecting to a network behind a captive
portal. It may also help if the captive portal access times out
after connecting, but this is less reliable.
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 the user to first accept an Acceptable Use Policy access require the user to accept an Acceptable Use Policy (AUP) and
(AUP) and / or provides billing information (such as their last name / or provides billing information (such as their last name and room
and room number in a hotel, credit card information, etc.) through a number in a hotel, credit card information, etc.) through a web
web interface. interface before the user can access the Internet.
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
o IP Redirection o IP Redirection
o HTTP Redirection o HTTP Redirection
o Restricted scope addresses o Restricted scope addresses
o Traffic blocking (until the user is authenticated) o Traffic blocking (until the user is authenticated)
In order to ensure that the user is unable to access the Internet In order to ensure that the user is unable to access the Internet
until they have satisfied the requirements, captive portals usually until they have satisfied the requirements, captive portals usually
implement IP based filters, or place the user in to a restricted VLAN implement IP based filters, or place the user into a restricted VLAN
(or restricted IP range) until after they have been authorized. (or restricted IP range) until after they have been authorized /
satisfied.
These techniques are very similar to attacks that protocols (such as
VPNs, DNSSEC, TLS) are designed to protect against. The interaction
of the these protections and the interception leads to poor user
experiences, such as long timeouts, inability to reach the captive
portal web page, etc. The interception may also leak user
information (for example, if the captive portal intercepts and logs
an HTTP Cookie, or URL of the form http://fred:password@example.com).
The user is often unaware of what is causing the issue (their browser
appears to hang, saying something like "Downloading Proxy Script", or
simply "The Internet doesn't work"), and they become frustrated.
This often results in them not purchasing the Internet access
provided by the captive portal.
2.1. DNS Redirection 2.1. DNS Redirection
The CP either intercepts all DNS traffic or advertises itself (for The CP either intercepts all DNS traffic or advertises itself (for
example using DHCP) as the recursive server for the network. Until example using DHCP) as the recursive server for the network. Until
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, is running their own resolver, or performing DNSSEC validation, is running their own resolver, is using
already has the DNS information cached. a VPN, or already has the DNS information cached.
2.2. HTTP Redirection 2.2. HTTP Redirection
In this implementation, the CP acts like a transparent HTTP proxy; In this implementation, the CP acts like a transparent HTTP proxy;
but 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.
This technique has a number of issues, including: This technique has a number of issues, including:
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o It doesn't work if the client has a VPN and / or proxies their web o It doesn't work if the client has a VPN and / or proxies their web
traffic to an external web proxy. traffic to an external web proxy.
2.3. IP Hijacking 2.3. IP Hijacking
In this scenario, the captive portal intercepts connections to any IP In this scenario, the captive portal intercepts connections to any IP
address. It spoofs the destination IP address and "pretends" to be address. It spoofs the destination IP address and "pretends" to be
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 user's private
information. information.
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. This is primarily intended to improve the user authentication page. This is primarily intended to improve the user
experience; for the foreseeable future captive portals will still experience; for the foreseeable future captive portals will still
need to implement the interception techniques to serve legacy need to implement the interception techniques to serve legacy
clients. clients.
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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 MUST 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). The remove the need to allow DNS from unauthenticated clients). The
DHCPv4 URI MUST contain an IPv4 address. DHCPv4 URI MUST contain an IPv4 address.
[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 users
use this to DNS Tunnel out. This would make the CP admin block would use this to DNS Tunnel out. This would make the CP admin block
external recursives).] external recursives).]
4. The Captive-Portal RA Option 4. The Captive-Portal RA Option
[ Ed: I'm far from an RA expert. I think there are only 8 bits for [Ed: I'm far from an RA expert. I think there are only 8 bits for
Type, is it worth burning an option code on this? I have also 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 specified that the option length should padded to multiples of 8 byte
to better align with the examples I've seen. Is this required / to better align with the examples I've seen. Is this required /
preferred, or is smaller RAs better? ] preferred, or is smaller RAs better? ]
This section describes the Captive-Portal Router Advertisement This section describes the Captive-Portal Router Advertisement
option. option.
0 1 2 3 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 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
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handled by the Operating System vendors / Application developers. ] handled by the Operating System vendors / Application developers. ]
The purpose of the Captive-Portal Option is to inform the operating The purpose of the Captive-Portal Option is to inform the operating
system and applications that they are behind a captive portal type system and applications that they are behind a captive portal type
device and will need to authenticate before getting network access device and will need to authenticate before getting network access
(and how to reach the authentication page). What is done with this (and how to reach the authentication page). What is done with this
information is left up to the operating system and application information is left up to the operating system and application
vendors. This document provides a very high level example of what vendors. This document provides a very high level example of what
could be done with this information. could be done with this information.
When the device discovers that it is behind a captive portal it Many operating systems / applications already include a "connectivity
test" to determine if they are behind a captive portal (for example,
attempting to fetch a specific URL and looking for a specific string
(such as "Success")). These tests sometimes fail or take a long time
to determine when they are behind a CP, but are usually effective for
determining that the captive portal has been satisfied. These tests
will continue to be needed, because there is currently no definitive
signal from the captive portal that it has been satisfied. The
connectivity test may also need to be used if the captive portal
times out the user session and needs the user to re-authenticate /
pay again. The operating system may still find the information about
the captive portal URI useful in this case.
When the device is informed that it is behind a captive portal it
SHOULD: 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
(other than those to the captive portal page and connectivity (other than those to the captive portal page and connectivity
checks). Existing connections should be quiesced (this will checks). Existing connections should be quiesced (this will
happen more often than some expect -- you buy 1h of Internet at a happen more often than some expect -- for example, the user
cafe and stay there for 3h -- this will "interrupt" you a few purchases 1 hour of Internet at a cafe and stays there for 3
times). hours -- this will "interrupt" the user a few times).
2. Present a dialog box to the user informing them hat they are 2. Present a dialog box to the user informing them that they are
behind a captive portal and ask if they wish to proceed. behind a 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, and without a proxy
send the user a cookie when they authenticate (so that the user server. If there is a VPN in place, this connection should be
can re-authenticate more easily in the future - the browser made outside of the VPN. Some captive portals send the user a
should keep these CP cookies separate from other cookies. cookie when they authenticate (so that the user can re-
authenticate more easily in the future - the browser should keep
these CP cookies separate from other cookies.
4. Once the user has authenticated normal IP connectivity should 4. Once the user has authenticated normal IP connectivity should
resume. This document does not define how to know that the user resume. This document does not define how to know that the user
has authenticated [ Ed: Should it? And option would be for the has authenticated [Ed: Should it? And option would be for the
"Thank you for paying" page to contain a unique string (e.g: "Thank you for paying" page to contain a unique string (e.g:
"CP_SATISFIED" ]. Operating system vendors may wish to provide a "CP_SATISFIED"]. Operating system vendors may wish to provide a
public service that their devices can use as a connectivity public service that their devices can use as a connectivity
check. check.
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.
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7. Security Considerations 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 an address of his choosing. this option and so force users to contact an address of his choosing.
As an attacker with this capability could simply list himself as the As an attacker with this capability could simply list himself as the
default gateway (and so intercept all the victim's traffic), this default gateway (and so intercept all the victim's traffic), this
does not provide them with significantly more capabilities. Fake does not provide them with significantly more capabilities. Fake
DHCP servers / fake RAs are currently a security concern - this DHCP servers / fake RAs are currently a security concern - this
doesn't make them any better or worse. 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 an open network
potentially be tracked using the techniques described in this could 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.) However, similar tracking can 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. technique does not 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. In addition, because the system knows that it validation, VPNs, etc. In addition, because the system knows that it
is behind a captive portal it can know not to send cookies, is behind a captive portal, it can know not to send cookies,
credentials, etc. credentials, etc.
8. 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 Lorenzo Thanks to Wes George for supplying the IPv6 text. Thanks to Lorenzo
and Erik for the V6 RA kick in the pants. and Erik for the V6 RA kick in the pants.
9. References 9. References
9.1. Normative References 9.1. Normative References
[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.
9.2. 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 03 to 04:
o Some text cleanup for readability.
o Some disclaimers about it working better on initial connection
versus CP timeout.
o Some more text explaining that CP interception is
indistinguishable from an attack.
o Connectivity Check test.
o Posting just before the draft cutoff - "I love deadlines. I love
the whooshing noise they make as they go by." -- Douglas Adams,
The Salmon of Doubt
From -02 to 03: From -02 to 03:
o Removed the DHCPv6 stuff (as suggested / requested by Erik Kline) o Removed the DHCPv6 stuff (as suggested / requested by Erik Kline)
o Simplified / cleaned up text (I'm inclined to waffle on, then trim o Simplified / cleaned up text (I'm inclined to waffle on, then trim
the fluff) the fluff)
o This was written on a United flight with in-flight WiFi - o This was written on a United flight with in-flight WiFi -
unfortnatly I couldn't use it because their CP was borked. unfortunately I couldn't use it because their CP was borked. :-P
From -01 to 02: From -01 to 02:
o Added the IPv6 RA stuff. 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.
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Olafur Gudmundsson Olafur Gudmundsson
Shinkuro Inc. Shinkuro Inc.
4922 Fairmont Av, Suite 250 4922 Fairmont Av, Suite 250
Bethesda, MD 20814 Bethesda, MD 20814
USA USA
Email: ogud@ogud.com Email: ogud@ogud.com
Paul Ebersman Paul Ebersman
Infoblox Comcast
Email: ebersman-ietf@dragon.net Email: ebersman-ietf@dragon.net
Steve Sheng Steve Sheng
Internet Corporation for Assigned Names and Numbers Internet Corporation for Assigned Names and Numbers
12025 Waterfront Drive, Suite 300 12025 Waterfront Drive, Suite 300
Los Angeles 90094 Los Angeles 90094
United States of America United States of America
Phone: +1.310.301.5800 Phone: +1.310.301.5800
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