draft-ietf-capport-rfc7710bis-02.txt   draft-ietf-capport-rfc7710bis-03.txt 
Network Working Group W. Kumari Network Working Group W. Kumari
Internet-Draft Google Internet-Draft Google
Obsoletes: 7710 (if approved) E. Kline Obsoletes: 7710 (if approved) E. Kline
Intended status: Standards Track Loon Intended status: Standards Track Loon
Expires: September 8, 2020 March 7, 2020 Expires: October 1, 2020 March 30, 2020
Captive-Portal Identification in DHCP / RA Captive-Portal Identification in DHCP / RA
draft-ietf-capport-rfc7710bis-02 draft-ietf-capport-rfc7710bis-03
Abstract Abstract
In many environments offering short-term or temporary Internet access In many environments offering short-term or temporary Internet access
(such as coffee shops), it is common to start new connections in a (such as coffee shops), it is common to start new connections in a
captive portal mode. This highly restricts what the customer can do captive portal mode. This highly restricts what the customer can do
until the customer has authenticated. until the customer has authenticated.
This document describes a DHCP option (and a Router Advertisement This document describes a DHCP option (and a Router Advertisement
(RA) extension) to inform clients that they are behind some sort of (RA) extension) to inform clients that they are behind some sort of
captive-portal device, and that they will need to authenticate to get captive-portal enforcement device, and that they will need to
Internet access. It is not a full solution to address all of the authenticate to get Internet access. It is not a full solution to
issues that clients may have with captive portals; it is designed to address all of the issues that clients may have with captive portals;
be used in larger solutions. The method of authenticating to, and it is designed to be used in larger solutions. The method of
interacting with the captive portal is out of scope of this document. authenticating to, and interacting with the captive portal is out of
scope of this document.
RFC7710 used DHCP code point 160. Due to a conflict, this document RFC7710 used DHCP code point 160. Due to a conflict, this document
specifies TBD. specifies TBD.
[ This document is being collaborated on in Github at: [ This document is being collaborated on in Github at:
https://github.com/capport-wg/7710bis. The most recent version of https://github.com/capport-wg/7710bis. The most recent version of
the document, open issues, etc should all be available here. The the document, open issues, etc should all be available here. The
authors (gratefully) accept pull requests. Text in square brackets authors (gratefully) accept pull requests. Text in square brackets
will be removed before publication. ] will be removed before publication. ]
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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 https://datatracker.ietf.org/drafts/current/. Drafts is at https://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 September 8, 2020.
This Internet-Draft will expire on October 1, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 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
(https://trustee.ietf.org/license-info) in effect on the date of (https://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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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. The Captive-Portal Option . . . . . . . . . . . . . . . . . . 3 2. The Captive-Portal Option . . . . . . . . . . . . . . . . . . 3
2.1. IPv4 DHCP Option . . . . . . . . . . . . . . . . . . . . 4 2.1. IPv4 DHCP Option . . . . . . . . . . . . . . . . . . . . 4
2.2. IPv6 DHCP Option . . . . . . . . . . . . . . . . . . . . 4 2.2. IPv6 DHCP Option . . . . . . . . . . . . . . . . . . . . 5
2.3. The Captive-Portal IPv6 RA Option . . . . . . . . . . . . 5 2.3. The Captive-Portal IPv6 RA Option . . . . . . . . . . . . 5
3. Precedence of API URIs . . . . . . . . . . . . . . . . . . . 6 3. Precedence of API URIs . . . . . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
4.1. IETF params Registration . . . . . . . . . . . . . . . . 6 4.1. IETF params Registration . . . . . . . . . . . . . . . . 6
4.1.1. Registry name: Captive Portal Unrestricted Identifier 6 4.1.1. Registry name: Captive Portal Unrestricted Identifier 6
4.2. BOOTP Vendor Extensions and DHCP Options Code Change . . 6 4.2. BOOTP Vendor Extensions and DHCP Options Code Change . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
7. Normative References . . . . . . . . . . . . . . . . . . . . 8 7. Normative References . . . . . . . . . . . . . . . . . . . . 8
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 10 Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 10
Appendix B. Changes from RFC 7710 . . . . . . . . . . . . . . . 10 Appendix B. Changes from RFC 7710 . . . . . . . . . . . . . . . 10
Appendix C. Observations From IETF 106 Network Experiment . . . 10 Appendix C. Observations From IETF 106 Network Experiment . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
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 (AUP) and / or provide device and agree to an Acceptable Use Policy (AUP) and / or provide
billing information before they can access the Internet. Regardless billing information before they can access the Internet. Regardless
of how that mechanism operates, this document provides functionality of how that mechanism operates, this document provides functionality
to allow the client to know when it is behind a captive portal and to allow the client to know when it is behind a captive portal and
how to contact it. how to contact it.
In order to present users with the payment or AUP pages, the captive- In order to present users with the payment or AUP pages, presently a
portal device has to intercept the user's connections and redirect captive-portal enforcement device has to intercept the user's
the user to the captive portal, using methods that are very similar connections and redirect the user to a captive portal server, using
to man-in-the-middle (MITM) attacks. As increasing focus is placed methods that are very similar to man-in-the-middle (MITM) attacks.
on security, and end nodes adopt a more secure stance, these As increasing focus is placed on security, and end nodes adopt a more
interception techniques will become less effective and/or more secure stance, these interception techniques will become less
intrusive. effective and/or more intrusive.
This document describes a DHCP ([RFC2131]) option (Captive-Portal) This document describes a DHCP ([RFC2131]) option (Captive-Portal)
and an IPv6 Router Advertisement (RA) ([RFC4861]) extension that and an IPv6 Router Advertisement (RA) ([RFC4861]) extension that
informs clients that they are behind a captive-portal device and how informs clients that they are behind a captive-portal enforcement
to contact it. device and how to contact an API for more information.
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. The Captive-Portal Option 2. The Captive-Portal Option
The Captive Portal DHCP / RA Option informs the client that it may be The Captive Portal DHCP / RA Option informs the client that it may be
behind a captive portal and provides the URI to access an API as behind a captive portal and provides the URI to access an API as
defined by [draft-ietf-capport-api]. This is primarily intended to defined by [draft-ietf-capport-api]. This is primarily intended to
improve the user experience by getting them to the captive portal improve the user experience by showing the user the captive portal
faster and more reliably. Note that, for the foreseeable future, information faster and more reliably. Note that, for the foreseeable
captive portals will still need to implement the interception future, captive portals will still need to implement the interception
techniques to serve legacy clients, and clients will need to perform techniques to serve legacy clients, and clients will need to perform
probing to detect captive portals. probing to detect captive portals.
Clients that support the Captive Portal DHCP option SHOULD include Clients that support the Captive Portal DHCP option SHOULD include
the option in the Parameter Request List in DHCPREQUEST messages. the option in the Parameter Request List in DHCPREQUEST messages.
DHCP servers MAY send the Captive Portal option without any explicit DHCP servers MAY send the Captive Portal option without any explicit
request. request.
In order to support multiple "classes" of clients (e.g. IPv4 only, In order to support multiple "classes" of clients (e.g. IPv4 only,
IPv6 only with DHCPv6 ([RFC3315]), IPv6 only with RA) the captive IPv6 only with DHCPv6 ([RFC3315]), and IPv6 only with RA) the captive
portal can provide the URI via multiple methods (IPv4 DHCP, IPv6 network can provision the client with the URI via multiple methods
DHCP, IPv6 RA). The captive portal operator SHOULD ensure that the (IPv4 DHCP, IPv6 DHCP, and IPv6 RA). The captive portal operator
URIs handed out are equivalent to reduce the chance of operational SHOULD ensure that the URIs provisioned by each method are equivalent
problems. The maximum length of the URI that can be carried in IPv4 to reduce the chance of operational problems. The maximum length of
DHCP is 255 bytes, so URIs longer than 255 bytes should not be used the URI that can be carried in IPv4 DHCP is 255 bytes, so URIs longer
in IPv6 DHCP or IPv6 RA. than 255 bytes should not be provisioned via IPv6 DHCP or IPv6 RA
either.
In all variants of this option, the URI MUST be that of the captive In all variants of this option, the URI MUST be that of the captive
portal API endpoint, conforming to the recommendations for such URIs portal API endpoint, conforming to the recommendations for such URIs
[draft-ietf-capport-api] (i.e. the URI SHOULD contain a DNS name and [draft-ietf-capport-api].
SHOULD reference a secure transport, e.g. https).
A captive portal MAY redirect requests that do not have an Accept A captive portal server MAY redirect requests that do not have an
header field ([RFC7231] Section 5.3) containing a field item whose Accept header field ([RFC7231] Section 5.3) containing a field item
content-type is "application/capport+json" to the URL conveyed in the whose content-type is "application/capport+json" to the URL conveyed
"user-portal-url" API key. When performing such content negotiation in the "user-portal-url" API key. When performing such content
([RFC7231] Section 3.4), captive portals need to keep in mind that negotiation ([RFC7231] Section 3.4), captive portals implementors
such responses might be cached, and therefore SHOULD include an need to keep in mind that such responses might be cached, and
appropriate Vary header field ([RFC7231] Section 7.1.4) or mark them therefore SHOULD include an appropriate Vary header field ([RFC7231]
explicitly uncacheable (for example, using Cache-Control: no-store Section 7.1.4) or mark them explicitly uncacheable (for example,
[RFC7234] Section 5.2.2.3). using Cache-Control: no-store [RFC7234] Section 5.2.2.3).
A captive portal MAY do content negotiation ([RFC7231] section 3.4) A captive portal MAY do content negotiation ([RFC7231] section 3.4)
and attempt to redirect clients querying without an explicit and attempt to redirect clients querying without an explicit
indication of support for the captive portal API content type (i.e. indication of support for the captive portal API content type (i.e.
without application/capport+json listed explicitly anywhere within an without application/capport+json listed explicitly anywhere within an
Accept header vis. [RFC7231] section 5.3). In so doing, the captive Accept header vis. [RFC7231] section 5.3). In so doing, the captive
portal SHOULD redirect the client to the value associated with the portal SHOULD redirect the client to the value associated with the
"user-portal-url" API key. "user-portal-url" API key.
The URI SHOULD NOT contain an IP address literal. The URI parameter The URI SHOULD NOT contain an IP address literal.
is not null terminated.
Networks with no captive portals MAY explicitly indicate this Networks with no captive portals MAY explicitly indicate this
condition by using this option with the IANA-assigned URI for this condition by using this option with the IANA-assigned URI for this
purpose (see Section 4.1.1). Clients observing the URI value purpose (see Section 4.1.1). Clients observing the URI value
"urn:ietf:params:capport-unrestricted" MAY forego time-consuming "urn:ietf:params:capport-unrestricted" MAY forego time-consuming
forms of captive portal detection. forms of captive portal detection.
2.1. IPv4 DHCP Option 2.1. IPv4 DHCP Option
The format of the IPv4 Captive-Portal DHCP option is shown below. The format of the IPv4 Captive-Portal DHCP option is shown below.
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| code | len | URI ... | | code | len | URI ... |
+------+------+------+------+------+-- --+-----+ +------+------+------+------+------+-- --+-----+
o Code: The Captive-Portal DHCPv4 Option (TBD) (one octet) o Code: The Captive-Portal DHCPv4 Option (TBD) (one octet)
o Len: The length, in octets of the URI. o Len: The length, in octets of the URI.
o URI: The URI for the captive portal API endpoint to which the user o URI: The URI for the captive portal API endpoint to which the user
should connect (encoded following the rules in [RFC3986]). should connect (encoded following the rules in [RFC3986]).
Note that the URI parameter is not null terminated.
2.2. IPv6 DHCP Option 2.2. IPv6 DHCP Option
The format of the IPv6 Captive-Portal DHCP option is shown below. The format of the IPv6 Captive-Portal DHCP option is shown below.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-code | option-len | | option-code | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. URI (variable length) . . URI (variable length) .
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o option-code: The Captive-Portal DHCPv6Option (103) (two octets) o option-code: The Captive-Portal DHCPv6Option (103) (two octets)
o option-len: The length, in octets of the URI. o option-len: The length, in octets of the URI.
o URI: The URI for the captive portal API endpoint to which the user o URI: The URI for the captive portal API endpoint to which the user
should connect (encoded following the rules in [RFC3986]). should connect (encoded following the rules in [RFC3986]).
See [RFC7227], Section 5.7 for more examples of DHCP Options with See [RFC7227], Section 5.7 for more examples of DHCP Options with
URIs. URIs.
Note that the URI parameter is not null terminated.
2.3. The Captive-Portal IPv6 RA Option 2.3. The Captive-Portal IPv6 RA Option
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | URI . | Type | Length | URI .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ .
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Type 37 Type 37
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 for the captive portal API endpoint to which the user URI The URI for the captive portal API endpoint to which the user
should connect. This MUST be padded with NULL (0x00) to make the should connect. This MUST be padded with NULL (0x00) to make the
total option length (including the Type and Length fields) a total option length (including the Type and Length fields) a
multiple of 8 bytes. multiple of 8 bytes.
Note that the URI parameter is not guaranteed to be null terminated.
3. Precedence of API URIs 3. Precedence of API URIs
A device may learn about Captive Portal API URIs through more than A device may learn about Captive Portal API URIs through more than
one of (or indeed all of) the above options. It is a network one of (or indeed all of) the above options. It is a network
configuration error if the learned URIs are not all identical. configuration error if the learned URIs are not all identical.
However, if the URIs learned are not in fact all identical the However, if the URIs learned are not in fact all identical the
captive device MUST prioritize URIs learned from network provisioning captive device MUST prioritize URIs learned from network provisioning
or configuration mechanisms before all other URIs. Specifically, or configuration mechanisms before all other URIs. Specifically,
URIs learned via any of the options in Section 2 should take URIs learned via any of the options in Section 2 should take
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page in a sandboxed environment and take other precautions, such as page in a sandboxed environment and take other precautions, such as
clearly labeling the page as untrusted. The means of sandboxing and clearly labeling the page as untrusted. The means of sandboxing and
user interface presenting this information is not covered in this user interface presenting this information is not covered in this
document - by its nature it is implementation specific and best left document - by its nature it is implementation specific and best left
to the application and user interface designers. to the application and user interface designers.
Devices and systems that automatically connect to an open network Devices and systems that automatically connect to an open network
could 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). However, similar tracking can already be their browser fingerprint). However, similar tracking can already be
performed with the standard captive portal mechanisms, so this performed with the presently common captive portal mechanisms, so
technique does not give the attackers more capabilities. this technique does not give the attackers more capabilities.
Captive portals are increasingly hijacking TLS connections to force Captive portals are increasingly hijacking TLS connections to force
browsers to talk to the portal. Providing the portal's URI via a browsers to talk to the portal. Providing the portal's URI via a
DHCP or RA option is a cleaner technique, and reduces user DHCP or RA option is a cleaner technique, and reduces user
expectations of being hijacked - this may improve security by making expectations of being hijacked - this may improve security by making
users more reluctant to accept TLS hijacking, which can be performed users more reluctant to accept TLS hijacking, which can be performed
from beyond the network associated with the captive portal. from beyond the network associated with the captive portal.
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
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