< draft-ietf-capport-rfc7710bis-00.txt   draft-ietf-capport-rfc7710bis-01.txt >
Network Working Group W. Kumari Network Working Group W. Kumari
Internet-Draft Google Internet-Draft Google
Updates: 7710 (if approved) E. Kline Obsoletes: 7710 (if approved) E. Kline
Intended status: Standards Track Loon Intended status: Standards Track Loon
Expires: January 3, 2020 July 2, 2019 Expires: July 15, 2020 January 12, 2020
Captive-Portal Identification in DHCP / RA Captive-Portal Identification in DHCP / RA
draft-ietf-capport-rfc7710bis-00 draft-ietf-capport-rfc7710bis-01
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
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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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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 January 3, 2020. This Internet-Draft will expire on July 15, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 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.
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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 . . . . . . . . . . . . . . . . . . . . 4
2.3. The Captive-Portal IPv6 RA Option . . . . . . . . . . . . 5 2.3. The Captive-Portal IPv6 RA Option . . . . . . . . . . . . 5
3. The Captive-Portal Link Relation Type . . . . . . . . . . . . 6 3. Precedence of API URIs . . . . . . . . . . . . . . . . . . . 6
4. Precedence of API URIs . . . . . . . . . . . . . . . . . . . 6 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 4.1. IETF params Registration . . . . . . . . . . . . . . . . 6
5.1. IETF params Registration . . . . . . . . . . . . . . . . 6 4.1.1. Registry name: Captive Portal Unrestricted Identifier 6
5.1.1. Registry name: Captive Portal Unrestricted Identifier 6 4.2. BOOTP Vendor Extensions and DHCP Options Code Change . . 6
5.1.2. Registry name: Captive Portal API Link Relation Type 7 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 7. Normative References . . . . . . . . . . . . . . . . . . . . 8
8. Normative References . . . . . . . . . . . . . . . . . . . . 8 Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 10
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 9 Appendix B. Changes from RFC 7710 . . . . . . . . . . . . . . . 10
Appendix B. Changes from RFC 7710 . . . . . . . . . . . . . . . 9 Appendix C. Observations From IETF 106 Network Experiment . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 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. It is billing information before they can access the Internet. It is
anticipated that the IETF will work on a more fully featured protocol anticipated that the IETF will work on a more fully featured protocol
at some point, to ease interaction with Captive Portals. Regardless at some point, to ease interaction with Captive Portals. Regardless
of how that protocol operates, it is expected that this document will of how that protocol operates, it is expected that this document will
provide needed functionality because the client will need to know provide needed functionality because the client will need to know
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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 getting them to the captive portal
faster and more reliably. Note that, for the foreseeable future, faster and more reliably. Note that, for the foreseeable future,
captive portals will still need to implement the interception 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
the option in the Parameter Request List in DHCPREQUEST messages.
DHCP servers MAY send the Captive Portal option without any explicit
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]), IPv6 only with RA) the captive
portal can provide the URI via multiple methods (IPv4 DHCP, IPv6 portal can provide the URI via multiple methods (IPv4 DHCP, IPv6
DHCP, IPv6 RA). The captive portal operator should ensure that the DHCP, IPv6 RA). The captive portal operator SHOULD ensure that the
URIs handed out are equivalent to reduce the chance of operational URIs handed out are equivalent to reduce the chance of operational
problems. The maximum length of the URI that can be carried in IPv4 problems. The maximum length of the URI that can be carried in IPv4
DHCP is 255 bytes, so URIs longer than 255 bytes should not be used DHCP is 255 bytes, so URIs longer than 255 bytes should not be used
in IPv6 DHCP or IPv6 RA. in IPv6 DHCP or IPv6 RA.
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
[cite:API] (i.e. the URI SHOULD contain a DNS name and SHOULD [draft-ietf-capport-api] (i.e. the URI SHOULD contain a DNS name and
reference a secure transport, e.g. https). SHOULD reference a secure transport, e.g. https).
A captive portal MAY redirect requests that do not have an Accept A captive portal MAY redirect requests that do not have an Accept
header field ([RFC7231] Section 5.3) containing a field item whose header field ([RFC7231] Section 5.3) containing a field item whose
content-type is "application/capport+json" to the URL conveyed in the content-type is "application/capport+json" to the URL conveyed in 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), captive portals need to keep in mind that ([RFC7231] Section 3.4), captive portals need to keep in mind that
such responses might be cached, and therefore SHOULD include an such responses might be cached, and therefore SHOULD include an
appropriate Vary header field ([RFC7231] Section 7.1.4) or mark them appropriate Vary header field ([RFC7231] Section 7.1.4) or mark them
explicitly uncacheable (for example, using Cache-Control: no-store explicitly uncacheable (for example, using Cache-Control: no-store
[RFC7234] Section 5.2.2.3). [RFC7234] Section 5.2.2.3).
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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. The URI parameter
is not null terminated. 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 5.1.1). 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.
Code Len Data Code Len Data
+------+------+------+------+------+-- --+-----+ +------+------+------+------+------+-- --+-----+
| code | len | URI ... | | code | len | 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.
3. The Captive-Portal Link Relation Type 3. Precedence of API URIs
Some captive portal network deployments may be unable to change, or
unwilling to risk changing, the network infrastructure necessary to
use any of the above options. In such deployments, when clear text
HTTP intercept and redirection are used, a Link relation header
([RFC8288], Section 3.3) MAY be inserted to convey to a HTTP client
(user agent) the associated Captive Portal API URI.
HTTP user agents MUST ignore this link relation in any context other
than when explicitly probing to detect the presence of a captive
portal. Failure to do so could allow an attacker to inject a Captive
Portal API URI other than the correct URI for a given network or for
networks where there is no captive portal present at all.
4. 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
precedence over any URI learned via a mechanism like the one precedence over any URI learned via some other mechanism, such as a
described in Section 3. redirect.
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. URI precedence in this situation is not owner or administrator. URI precedence in this situation is not
specified by this document. specified by this document.
5. IANA Considerations 4. IANA Considerations
This document requests two new IETF URN protocol parameter This document requests two new IETF URN protocol parameter
([RFC3553]) entries. ([RFC3553]) entries. This document also requests a reallocation of
DHCPv4 option codes (see Appendix C for background).
Thanks IANA! Thanks IANA!
5.1. IETF params Registration 4.1. IETF params Registration
5.1.1. Registry name: Captive Portal Unrestricted Identifier 4.1.1. Registry name: Captive Portal Unrestricted Identifier
Registry name: Captive Portal Unrestricted Identifier Registry name: Captive Portal Unrestricted Identifier
URN: urn:ietf:params:capport-unrestricted URN: urn:ietf:params:capport-unrestricted
Specification: RFC TBD (this document) Specification: RFC TBD (this document)
Repository: RFC TBD (this document) Repository: RFC TBD (this document)
Index value: Only one value is defined (see URN above). No hierarchy Index value: Only one value is defined (see URN above). No hierarchy
is defined and therefore no sub-namespace registrations are possible. is defined and therefore no sub-namespace registrations are possible.
5.1.2. Registry name: Captive Portal API Link Relation Type 4.2. BOOTP Vendor Extensions and DHCP Options Code Change
Registry name: Captive Portal API Link Relation Type
URN: urn:ietf:params:capport-api [ RFC Ed: Please remove before publication: RFC7710 uses DHCP Code
160 -- unfortunately, it was discovered that this option code is
already widely used by Polycom (see appendix). Option 114 (URL) is
currently assigned to Apple (RFC3679, Section 3.2.3 - Contact: Dieter
Siegmund, dieter@apple.com - Reason to recover: Never published in an
RFC) Tommy Pauly (Apple) and Dieter Siegmund confirm that this
codepoint hasn't been used, and Apple is willing to relinquish it for
use in CAPPORT. Please see thread:
https://mailarchive.ietf.org/arch/msg/captive-portals/
TmqQz6Ma_fznD3XbhwkH9m2dB28 for more background. ]
Specification: RFC TBD (this document) The IANA is requested to update the "BOOTP Vendor Extensions and DHCP
Options" registry (https://www.iana.org/assignments/bootp-dhcp-
parameters/bootp-dhcp-parameters.xhtml) as follows.
Repository: RFC TBD (this document) Tag: 114
Name: DHCP Captive-Portal
Data Length: N
Meaning: DHCP Captive-Portal
Reference: [THIS-RFC]
Index value: Only one value is defined (see URN above). No hierarchy Tag: 160
is defined and therefore no sub-namespace registrations are possible. Name: REMOVED/Unassigned
Data Length:
Meaning:
Reference: [RFC7710][Deprecated]
6. Security Considerations 5. Security Considerations
An attacker with the ability to inject DHCP messages, RAs, or HTTP An attacker with the ability to inject DHCP messages or RAs could
headers into cleartext HTTP communications could include an option or include an option from this document to force users to contact an
link relation from this document and so 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 himself as the default gateway (and so intercept all the simply list himself as the default gateway (and so intercept all the
victim's traffic); this does not provide them with significantly more victim's traffic); this does not provide them with significantly more
capabilities, but because this document removes the need for 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. As the operating systems and application that make use of attack. As the operating systems and application 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) they can render the
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
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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. By handing out a URI using which is protected with credentials, etc. By handing out a URI using which is protected with
TLS, the captive portal operator can attempt to reassure the user TLS, the captive portal operator can attempt to reassure the user
that the captive portal is not malicious. that the captive portal is not malicious.
Operating systems should conduct all interactions with the API in a Operating systems should conduct all interactions with the API in a
sand-boxed environment and with a configuration that minimizes sand-boxed environment and with a configuration that minimizes
tracking risks. tracking risks.
7. Acknowledgements 6. Acknowledgements
This document is a -bis of RFC7710. Thanks to all of the original This document is a -bis of RFC7710. Thanks to all of the original
authors (Warren Kumari, Olafur Gudmundsson, Paul Ebersman, Steve authors (Warren Kumari, Olafur Gudmundsson, Paul Ebersman, Steve
Sheng), and original contributors. Sheng), and original contributors.
Also thanks to the CAPPORT WG for all of the discussion and Also thanks to the CAPPORT WG for all of the discussion and
improvements. improvements including contributions and review from Lorenzo Colitti,
Remi Nguyen Van, and Tommy Pauly.
8. Normative References 7. References
7.1. 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, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc- DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>. editor.org/info/rfc2119>.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", [RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997, RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/info/rfc2131>. <https://www.rfc-editor.org/info/rfc2131>.
skipping to change at page 9, line 35 skipping to change at page 9, line 40
[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, [RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching", Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
RFC 7234, DOI 10.17487/RFC7234, June 2014, RFC 7234, DOI 10.17487/RFC7234, June 2014,
<https://www.rfc-editor.org/info/rfc7234>. <https://www.rfc-editor.org/info/rfc7234>.
[RFC7710] Kumari, W., Gudmundsson, O., Ebersman, P., and S. Sheng, [RFC7710] Kumari, W., Gudmundsson, O., Ebersman, P., and S. Sheng,
"Captive-Portal Identification Using DHCP or Router "Captive-Portal Identification Using DHCP or Router
Advertisements (RAs)", RFC 7710, DOI 10.17487/RFC7710, Advertisements (RAs)", RFC 7710, DOI 10.17487/RFC7710,
December 2015, <https://www.rfc-editor.org/info/rfc7710>. December 2015, <https://www.rfc-editor.org/info/rfc7710>.
[RFC8288] Nottingham, M., "Web Linking", RFC 8288, 7.2. URIs
DOI 10.17487/RFC8288, October 2017, <https://www.rfc-
editor.org/info/rfc8288>. [1] https://tickets.meeting.ietf.org/wiki/IETF106network#Experiments
[2] https://tickets.meeting.ietf.org/wiki/CAPPORT
[3] https://community.polycom.com/t5/VoIP-SIP-Phones/DHCP-
Standardization-160-vs-66/td-p/72577
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 initial to -00. From initial to -00.
o Import of RFC7710. o Import of RFC7710.
From -00 to -01.
o Remove link-relation text.
o Clarify option should be in DHCPREQUEST parameter list.
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 SHOULD 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. Added urn:ietf:params:capport-api URN. Appendix C. Observations From IETF 106 Network Experiment
During IETF 106 in Singapore an experiment [1] enabling Captive
Portal API compatible clients to discover a venue-info-url (see
experiment description [2] for more detail) revealed that some
Polycom devices on the same network made use of DHCPv4 option code
160 for other purposes [3].
The presence of DHCPv4 Option code 160 holding a value indicating the
Captive Portal API URL caused these devices to not function as
desired. For this reason, this document requests IANA deprecate
option code 160 and reallocate different value to be used for the
Captive Portal API URL.
Authors' Addresses Authors' Addresses
Warren Kumari Warren Kumari
Google Google
1600 Amphitheatre Parkway 1600 Amphitheatre Parkway
Mountain View, CA 94043 Mountain View, CA 94043
US US
Email: warren@kumari.net Email: warren@kumari.net
Erik Kline Erik Kline
Loon Loon
1600 Amphitheatre Parkway 1600 Amphitheatre Parkway
Mountain View, CA 94043 Mountain View, CA 94043
US US
Email: ek@google.com Email: ek@loon.com
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