< draft-wkumari-dhc-capport-04.txt   draft-wkumari-dhc-capport-05.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: January 5, 2015 Shinkuro Inc. Expires: March 12, 2015 Shinkuro Inc.
P. Ebersman P. Ebersman
Comcast Comcast
S. Sheng S. Sheng
ICANN ICANN
July 4, 2014 September 8, 2014
Captive-Portal identification in DHCP / RA Captive-Portal identification in DHCP / RA
draft-wkumari-dhc-capport-04 draft-wkumari-dhc-capport-05
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 and / or terms of service, provided payment information and / or
authenticated. authenticated.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on January 5, 2015. This Internet-Draft will expire on March 12, 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
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publication of this document. Please review these documents publication of this document. Please review these documents
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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 . . . . . . . . . . . . . . . . . . . . . 4 2.1. DNS Redirection . . . . . . . . . . . . . . . . . . . . . 4
2.2. HTTP Redirection . . . . . . . . . . . . . . . . . . . . 4 2.2. HTTP Redirection . . . . . . . . . . . . . . . . . . . . 4
2.3. IP Hijacking . . . . . . . . . . . . . . . . . . . . . . 5 2.3. IP Hijacking . . . . . . . . . . . . . . . . . . . . . . 4
3. The Captive-Portal DHCP Option . . . . . . . . . . . . . . . 5 3. The Captive-Portal DHCP Option . . . . . . . . . . . . . . . 5
4. The Captive-Portal RA Option . . . . . . . . . . . . . . . . 6 4. The Captive-Portal RA Option . . . . . . . . . . . . . . . . 5
5. Use of the Captive-Portal Option . . . . . . . . . . . . . . 6 5. Use of the Captive-Portal Option . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 9. Normative References . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 9 Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
In many environments, users need to connect to a captive portal In many environments, users need to connect to a captive portal
device and agree to an acceptable use policy and / or provide billing device and agree to an acceptable use policy and / or provide billing
information 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
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These techniques are very similar to attacks that protocols (such as These techniques are very similar to attacks that protocols (such as
VPNs, DNSSEC, TLS) are designed to protect against. The interaction VPNs, DNSSEC, TLS) are designed to protect against. The interaction
of the these protections and the interception leads to poor user of the these protections and the interception leads to poor user
experiences, such as long timeouts, inability to reach the captive experiences, such as long timeouts, inability to reach the captive
portal web page, etc. The interception may also leak user portal web page, etc. The interception may also leak user
information (for example, if the captive portal intercepts and logs information (for example, if the captive portal intercepts and logs
an HTTP Cookie, or URL of the form http://fred:password@example.com). 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 The user is often unaware of what is causing the issue (their browser
appears to hang, saying something like "Downloading Proxy Script", or appears to hang, saying something like "Downloading Proxy Script", or
simply "The Internet doesn't work"), and they become frustrated. simply "The Internet doesn't work"), and they become frustrated.
This often results in them not purchasing the Internet access This may results in them not purchasing the Internet access provided
provided by the captive portal. 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
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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 issues similar to the HTTP solution, but may also
break other protocols, and may expose more of the user's 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 an
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 (until such time that most
need to implement the interception techniques to serve legacy systems implement this technique) captive portals will still need to
clients. implement the interception techniques to serve legacy clients.
The format of the DHCP Captive-Portal DHCP option is shown below. The format of the DHCP Captive-Portal DHCP option is shown below.
Code Len Data Code Len Data
+------+------+------+------+------+-- --+-----+ +------+------+------+------+------+-- --+-----+
| code | len | URI ... | | code | len | URI ... |
+------+------+------+------+------+-- --+-----+ +------+------+------+------+------+-- --+-----+
o Code: The Captive-Portal DHCP Option (TBA1 for DHCPv4, TBA2 for o Code: The Captive-Portal DHCP Option (TBA1 for DHCPv4, TBA2 for
DHCPv6) 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 MUST be a URL with an IP-literal for the host portion (to The URI MUST NOT contain a DNS name, in order to not require the CP
remove the need to allow DNS from unauthenticated clients). The to access DNS queries from an unauthenticated user. Rather, if IPv4
DHCPv4 URI MUST contain an IPv4 address. is supported in the network, one option's URI MUST contain an IPv4
address literal, and if IPv6 is supported in the network, one
option's URI MUST contain an IPv6 address literal. Note that this
implies that a dual stack network would include two such options in
its DHCP reply or RA.
[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 users want to force users to use the CP's provided DNS) and some users
would 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
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. . . .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Captive-Portal RA Option Format Figure 2: Captive-Portal RA Option Format
Type TBA3 Type TBA3
Length 8-bit unsigned integer. The length of the option (including Length 8-bit unsigned integer. The length of the option (including
the Type and Length fields) in units of 8 bytes. the Type and Length fields) in units of 8 bytes.
URI The URI of the authentication page that the user should connect URI The URI (containing an IPv6 literal) of the authentication page
to. This should be padded with NULL (0x0) to make the total that the user should connect to. This should be padded with NULL
option length (including the Type and Length fields) a multiple of (0x0) to make the total option length (including the Type and
8 bytes. Length fields) a multiple of 8 bytes.
5. Use of the Captive-Portal Option 5. Use of the Captive-Portal Option
[ED NOTE: This section is, and probably will remain, fairly hand [ED NOTE: This option provides notice to the OS / User applications
wavy. This option provides notice to the OS / User applications that that there is a CP. Because of differences in UI design between
there is a CP, but I think that the UI / etc is best designed / Operating Systems, the exact behaviour by OS and Applications is left
handled by the Operating System vendors / Application developers. ] to the OS vendor/Application Developer.]
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.
Many operating systems / applications already include a "connectivity Many operating systems / applications already include a "connectivity
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purchases 1 hour of Internet at a cafe and stays there for 3 purchases 1 hour of Internet at a cafe and stays there for 3
hours -- this will "interrupt" the user a few times). hours -- this will "interrupt" the user a few times).
2. Present a dialog box to the user informing them that 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, and without a proxy configured with a separate cookie store, and without a proxy
server. If there is a VPN in place, this connection should be server. If there is a VPN in place, this connection should be
made outside of the VPN. Some captive portals send the user a made outside of the VPN and the user should be informed that
cookie when they authenticate (so that the user can re- connection is outside the VPN. Some captive portals send the
authenticate more easily in the future - the browser should keep user a 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. 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. The CP success page should contain a string, e.g
has authenticated [Ed: Should it? And option would be for the "CP_SATISFIED." The OS can then use this string to provide
"Thank you for paying" page to contain a unique string (e.g: further information to the user.
"CP_SATISFIED"]. Operating system vendors may wish to provide a
public service that their devices can use as a connectivity
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.
6. IANA Considerations 6. IANA Considerations
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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 IPv6 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 Thanks for Fred Baker for detailed review and comments.
9.1. Normative References 9. 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
[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. Appendix A. Changes / Author Notes.
[RFC Editor: Please remove this section before publication ] [RFC Editor: Please remove this section before publication ]
From 04 to 05:
o Integrated comments, primarily from Fred Baker.
From 03 to 04: From 03 to 04:
o Some text cleanup for readability. o Some text cleanup for readability.
o Some disclaimers about it working better on initial connection o Some disclaimers about it working better on initial connection
versus CP timeout. versus CP timeout.
o Some more text explaining that CP interception is o Some more text explaining that CP interception is
indistinguishable from an attack. indistinguishable from an attack.
 End of changes. 21 change blocks. 
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