draft-ietf-capport-rfc7710bis-07.txt   draft-ietf-capport-rfc7710bis-08.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 Updates: 3679 (if approved) Loon
Expires: November 24, 2020 May 23, 2020 Intended status: Standards Track June 23, 2020
Expires: December 25, 2020
Captive-Portal Identification in DHCP / RA Captive-Portal Identification in DHCP / RA
draft-ietf-capport-rfc7710bis-07 draft-ietf-capport-rfc7710bis-08
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 user can do
until the customer has authenticated. until the user has satified the Captive Portal conditions.
This document describes a DHCPv4 and DHCPv6 option and a Router This document describes a DHCPv4 and DHCPv6 option and a Router
Advertisement (RA) option to inform clients that they are behind some Advertisement (RA) option to inform clients that they are behind some
sort of captive-portal enforcement device, and that they will need to sort of captive-portal enforcement device, and that they will need to
authenticate to get Internet access. It is not a full solution to satify the Captive Portal conditions to get Internet access. It is
address all of the issues that clients may have with captive portals; not a full solution to address all of the issues that clients may
it is designed to be one component of a standardized approach for have with captive portals; it is designed to be one component of a
hosts to interact with such portals. While this document defines how standardized approach for hosts to interact with such portals. While
the network operator may convey the captive portal API endpoint to this document defines how the network operator may convey the captive
hosts, the specific methods of authenticating to, and interacting portal API endpoint to hosts, the specific methods of satisfying and
with the captive portal are out of scope of this document. interacting with the captive portal are out of scope of this
document.
This document replaces RFC 7710. RFC 7710 used DHCP code point 160. This document replaces [RFC7710]. [RFC7710] used DHCP code point
Due to a conflict, this document specifies 114. 160. Due to a conflict, this document specifies 114. Consequently,
this document also updates [RFC3679].
[ 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. ]
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 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 November 24, 2020. This Internet-Draft will expire on December 25, 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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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
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 . . . . . . . . . . . . . . . . . . . . 5 2.2. IPv6 DHCP Option . . . . . . . . . . . . . . . . . . . . 5
2.3. The Captive-Portal IPv6 RA Option . . . . . . . . . . . . 6 2.3. The Captive-Portal IPv6 RA Option . . . . . . . . . . . . 6
3. Precedence of API URIs . . . . . . . . . . . . . . . . . . . 6 3. Precedence of API URIs . . . . . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
4.1. Captive Portal Unrestricted Identifier . . . . . . . . . 7 4.1. Captive Portal Unrestricted Identifier . . . . . . . . . 7
4.2. BOOTP Vendor Extensions and DHCP Options Code Change . . 7 4.2. BOOTP Vendor Extensions and DHCP Options Code Change . . 7
4.3. Update DHCPv6 and IPv6 ND Options Registries . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9 7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 10 7.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 11 Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 11
Appendix B. Changes from RFC 7710 . . . . . . . . . . . . . . . 11 Appendix B. Changes from RFC 7710 . . . . . . . . . . . . . . . 12
Appendix C. Observations From IETF 106 Network Experiment . . . 12 Appendix C. Observations From IETF 106 Network Experiment . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
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
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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 ([RFC8415]), and IPv6 only with RA) the captive IPv6 only with DHCPv6 ([RFC8415]), and IPv6 only with RA) the captive
network can provision the client with the URI via multiple methods network can provision the client with the URI via multiple methods
(IPv4 DHCP, IPv6 DHCP, and IPv6 RA). The captive portal operator (IPv4 DHCP, IPv6 DHCP, and IPv6 RA). The captive portal operator
SHOULD ensure that the URIs provisioned by each method are equivalent SHOULD ensure that the URIs provisioned by each method are identical
to reduce the chance of operational problems. The maximum length of to reduce the chance of operational problems. As the maximum length
the URI that can be carried in IPv4 DHCP is 255 bytes, so URIs longer of the URI that can be carried in IPv4 DHCP is 255 bytes, URIs longer
than 255 bytes should not be provisioned via IPv6 DHCP nor IPv6 RA than this SHOULD NOT be provisioned by any of the IPv6 options
options. described in this document. In IPv6-only environments this
restriction can be relaxed.
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 [draft-ietf-capport-api].
[draft-ietf-capport-api].
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. When performing such content negotiation "user-portal-url" API key. When performing such content negotiation
([RFC7231] Section 3.4), implementors of captive portals need to keep ([RFC7231] Section 3.4), implementors of captive portals need to keep
in mind that such responses might be cached, and therefore SHOULD in mind that such responses might be cached, and therefore SHOULD
include an appropriate Vary header field ([RFC7231] Section 7.1.4) or include an appropriate Vary header field ([RFC7231] Section 7.1.4) or
mark them explicitly uncacheable (for example, using Cache-Control: set the Cache-Control header field in any responses to "private", or
no-store [RFC7234] Section 5.2.2.3). a more restrictive value such as "no-store" [RFC7234]
Section 5.2.2.3).
The URI SHOULD NOT contain an IP address literal. Exceptions to this The URI SHOULD NOT contain an IP address literal. Exceptions to this
might include networks with only one operational IP address family might include networks with only one operational IP address family
where DNS is either not available or not fully functional until the where DNS is either not available or not fully functional until the
captive portal has been satisfied. captive portal has been satisfied. Use of iPAddress certificates
([RFC3779]) adds considerations that are out of scope for this
document.
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. Clients observing the URI value purpose. 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.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Len | URI (variable length) ... | | Code | Len | URI (variable length) ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ...URI continued... . . ...URI continued... .
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Code: The Captive-Portal DHCPv4 Option (114) (one octet) o Code: The Captive-Portal DHCPv4 Option (114) (one octet)
o Len: The length (one octet), in octets of the URI. o Len: The length (one octet), 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 [RFC2132], Section 2 for more on the format of IPv4 DHCP options. See [RFC2132], Section 2 for more on the format of IPv4 DHCP options.
Note that the URI parameter is not null terminated. Note that the URI parameter is not null terminated.
2.2. IPv6 DHCP Option 2.2. IPv6 DHCP Option
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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. See [RFC8415], Section 21.1 for more on the format of IPv6 URIs. See [RFC8415], Section 21.1 for more on the format of IPv6
DHCP options. DHCP options.
Note that the URI parameter is not null terminated. Note that the URI parameter is not null terminated.
The maximum length of the URI that can be carried in IPv4 DHCP is 255 As the maximum length of the URI that can be carried in IPv4 DHCP is
bytes, so URIs longer than 255 bytes should not be provisioned via 255 bytes, URIs longer than this SHOULD NOT be provisioned via IPv6
IPv6 DHCP options. DHCP options.
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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. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Captive-Portal RA Option Format Figure 2: Captive-Portal RA Option Format
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 NUL (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. Note that the URI parameter is not guaranteed to be null terminated.
The maximum length of the URI that can be carried in IPv4 DHCP is 255 As the maximum length of the URI that can be carried in IPv4 DHCP is
bytes, so URIs longer than 255 bytes should not be provisioned via 255 bytes, URIs longer than this SHOULD NOT be provisioned via IPv6
IPv6 RA options. RA options.
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. Implementations can one of (or indeed all of) the above options. Implementations can
select their own precedence order (e.g., prefer one of the IPv6 select their own precedence order (e.g., prefer one of the IPv6
options before the DHCPv4 option, or vice versa, et cetera). options before the DHCPv4 option, or vice versa, et cetera).
If the URIs learned via more than one option described in Section 2 If the URIs learned via more than one option described in Section 2
are not all identical, this condition SHOULD be logged for the device are not all identical, this condition should be logged for the device
owner or administrator; it is a network configuration error if the owner or administrator; it is a network configuration error if the
learned URIs are not all identical. learned URIs are not all identical.
4. IANA Considerations 4. IANA Considerations
This document requests one new IETF URN protocol parameter This document requests one new IETF URN protocol parameter
([RFC3553]) entry. This document also requests a reallocation of ([RFC3553]) entry. This document also requests a reallocation of
DHCPv4 option codes (see Appendix C for background). DHCPv4 option codes (see Appendix C for background).
Thanks IANA! Thanks IANA!
4.1. Captive Portal Unrestricted Identifier 4.1. Captive Portal Unrestricted Identifier
This document registers a new entry under the IETF URN Sub-namespace This document registers a new entry under the IETF URN Sub-namespace
for Registered Protocol Parameter Identifiers defined in [RFC3553]: for Registered Protocol Parameter Identifiers defined in [RFC3553]:
Registered Parameter Identifier: capport:unrestricted Registered Parameter Identifier: capport:unrestricted
Reference: RFC TBD (this document) Reference: RFC TBD (this document)
IANA Registry Reference: [RFC3553] IANA Registry Reference: RFC TBD (this document)
Only one value is defined (see URN above). No hierarchy is defined Only one value is defined (see URN above). No hierarchy is defined
and therefore no sub-namespace registrations are possible. and therefore no sub-namespace registrations are possible.
4.2. BOOTP Vendor Extensions and DHCP Options Code Change 4.2. BOOTP Vendor Extensions and DHCP Options Code Change
[ RFC Ed: Please remove before publication: RFC7710 uses DHCP Code [ RFC Ed: Please remove before publication: RFC7710 uses DHCP Code
160 -- unfortunately, it was discovered that this option code is 160 -- unfortunately, it was discovered that this option code is
already widely used by Polycom (see appendix). Option 114 (URL) is already widely used by Polycom (see appendix). Option 114 (URL) is
currently assigned to Apple (RFC3679, Section 3.2.3 - Contact: Dieter currently assigned to Apple (RFC3679, Section 3.2.3 - Contact: Dieter
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The IANA is requested to update the "BOOTP Vendor Extensions and DHCP The IANA is requested to update the "BOOTP Vendor Extensions and DHCP
Options" registry (https://www.iana.org/assignments/bootp-dhcp- Options" registry (https://www.iana.org/assignments/bootp-dhcp-
parameters/bootp-dhcp-parameters.xhtml) as follows. parameters/bootp-dhcp-parameters.xhtml) as follows.
Tag: 114 Tag: 114
Name: DHCP Captive-Portal Name: DHCP Captive-Portal
Data Length: N Data Length: N
Meaning: DHCP Captive-Portal Meaning: DHCP Captive-Portal
Reference: [THIS-RFC] Reference: [THIS-RFC]
Tag: 160
Name: REMOVED/Unassigned Tag: 160
Data Length: Name: Unassigned
Meaning: Data Length:
Reference: [THIS-RFC][RFC7710] Meaning: Previously assigned by RFC7710; known to also be used by Polycom.
Reference: [THIS-RFC][RFC7710]
4.3. Update DHCPv6 and IPv6 ND Options Registries
This document requests that the DHCPv6 and IPv6 ND options previously
registered in [RFC7710] be updated to reference this document.
5. Security Considerations 5. Security Considerations
By removing or reducing the need for captive portals to perform MITM By removing or reducing the need for captive portals to perform MITM
hijacking, this mechanism improves security by making the portal and hijacking, this mechanism improves security by making the portal and
its actions visible, rather than hidden, and reduces the likelihood its actions visible, rather than hidden, and reduces the likelihood
that users will disable useful security safeguards like DNSSEC that users will disable useful security safeguards like DNSSEC
validation, VPNs, etc. In addition, because the system knows that it validation, VPNs, etc in order to interact with the captive portal.
is behind a captive portal, it can know not to send cookies, In addition, because the system knows that it is behind a captive
credentials, etc. By handing out a URI which is protected with TLS, portal, it can know not to send cookies, credentials, etc. By
the captive portal operator can attempt to reassure the user that the handing out a URI which is protected with TLS, the captive portal
captive portal is not malicious. operator can attempt to reassure the user that the captive portal is
not malicious.
Clients processing these options SHOULD validate that the option's
contents conform to the validation requirements for URIs, including
[RFC3986].
Each of the options described in this document is presented to a node Each of the options described in this document is presented to a node
using the same protocols used to provision other information critical using the same protocols used to provision other information critical
to the node's successful configuration on a network. The security to the node's successful configuration on a network. The security
considerations applicable to each of these provisioning mechanisms considerations applicable to each of these provisioning mechanisms
also apply when the node is attempting to learn the information also apply when the node is attempting to learn the information
conveyed in these options. In the absence of security measures like conveyed in these options. In the absence of security measures like
RA Guard ([RFC6105], [RFC7113]) or DHCP Shield [RFC7610], an attacker RA Guard ([RFC6105], [RFC7113]) or DHCP Shield [RFC7610], an attacker
could inject, modify, or block DHCP messages or RAs. could inject, modify, or block DHCP messages or RAs.
An attacker with the ability to inject DHCP messages or RAs could An attacker with the ability to inject DHCP messages or RAs could
include an option from this document to force users to contact an include an option from this document to force users to contact an
address of his choosing. As an attacker with this capability could address of his choosing. As an attacker with this capability could
simply list themselves as the default gateway (and so intercept all simply list themselves as the default gateway (and so intercept all
the victim's traffic); this does not provide them with significantly the victim's traffic); this does not provide them with significantly
more capabilities, but because this document removes the need for more capabilities, but because this document removes the need for
interception, the attacker may have an easier time performing the interception, the attacker may have an easier time performing the
attack. attack.
However, as the operating systems and application that make use of However, as the operating systems and application(s) that make use of
this information know that they are connecting to a captive-portal this information know that they are connecting to a captive-portal
device (as opposed to intercepted connections) they can render the device (as opposed to intercepted connections where the OS/
page in a sandboxed environment and take other precautions, such as application may not know that they are connecting to a captive portal
clearly labeling the page as untrusted. The means of sandboxing and or hostile device) they can render the page in a sandboxed
user interface presenting this information is not covered in this environment and take other precautions, such as clearly labeling the
document - by its nature it is implementation specific and best left page as untrusted. The means of sandboxing and user interface
to the application and user interface designers. presenting this information is not covered in this document - by its
nature it is implementation specific and best left 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 re-satisfy the Captive
their browser fingerprint). However, similar tracking can already be Portal conditions, or exposing their browser fingerprint). However,
performed with the presently common captive portal mechanisms, so similar tracking can already be performed with the presently common
this technique does not give the attackers more capabilities. captive portal mechanisms, so 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.
6. Acknowledgements 6. Acknowledgements
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May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters, Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018, RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>. <https://www.rfc-editor.org/info/rfc8415>.
7.2. Informative References 7.2. Informative References
[RFC3679] Droms, R., "Unused Dynamic Host Configuration Protocol
(DHCP) Option Codes", RFC 3679, DOI 10.17487/RFC3679,
January 2004, <https://www.rfc-editor.org/info/rfc3679>.
[RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
Addresses and AS Identifiers", RFC 3779,
DOI 10.17487/RFC3779, June 2004,
<https://www.rfc-editor.org/info/rfc3779>.
[RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J. [RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.
Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105, Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
DOI 10.17487/RFC6105, February 2011, DOI 10.17487/RFC6105, February 2011,
<https://www.rfc-editor.org/info/rfc6105>. <https://www.rfc-editor.org/info/rfc6105>.
[RFC7113] Gont, F., "Implementation Advice for IPv6 Router [RFC7113] Gont, F., "Implementation Advice for IPv6 Router
Advertisement Guard (RA-Guard)", RFC 7113, Advertisement Guard (RA-Guard)", RFC 7113,
DOI 10.17487/RFC7113, February 2014, DOI 10.17487/RFC7113, February 2014,
<https://www.rfc-editor.org/info/rfc7113>. <https://www.rfc-editor.org/info/rfc7113>.
skipping to change at page 11, line 46 skipping to change at page 12, line 19
o Clarify option should be in DHCPREQUEST parameter list. o Clarify option should be in DHCPREQUEST parameter list.
o Uppercase some SHOULDs. o Uppercase some SHOULDs.
Appendix B. Changes from RFC 7710 Appendix B. Changes from RFC 7710
This document incorporates the following changes from [RFC7710]. This document incorporates the following changes from [RFC7710].
1. Clarify that IP string literals are NOT RECOMMENDED. 1. Clarify that IP string literals are NOT RECOMMENDED.
2. Clarify that the option URI SHOULD be that of the captive portal 2. Clarify that the option URI MUST be that of the captive portal
API endpoint. API endpoint.
3. Clarify that captive portals MAY do content negotiation. 3. Clarify that captive portals MAY do content negotiation.
4. Added text about Captive Portal API URI precedence in the event 4. Added text about Captive Portal API URI precedence in the event
of a network configuration error. of a network configuration error.
5. Added urn:ietf:params:capport:unrestricted URN. 5. Added urn:ietf:params:capport:unrestricted URN.
6. Notes that the DHCP Code changed from 160 to 114. 6. Notes that the DHCPv4 Option Code changed from 160 to 114.
Appendix C. Observations From IETF 106 Network Experiment Appendix C. Observations From IETF 106 Network Experiment
During IETF 106 in Singapore an experiment [1] enabling Captive During IETF 106 in Singapore an experiment [1] enabling Captive
Portal API compatible clients to discover a venue-info-url (see Portal API compatible clients to discover a venue-info-url (see
experiment description [2] for more detail) revealed that some experiment description [2] for more detail) revealed that some
Polycom devices on the same network made use of DHCPv4 option code Polycom devices on the same network made use of DHCPv4 option code
160 for other purposes [3]. 160 for other purposes [3].
The presence of DHCPv4 Option code 160 holding a value indicating the The presence of DHCPv4 Option code 160 holding a value indicating the
 End of changes. 29 change blocks. 
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