draft-ietf-capport-rfc7710bis-03.txt   draft-ietf-capport-rfc7710bis-04.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: October 1, 2020 March 30, 2020 Expires: October 30, 2020 April 28, 2020
Captive-Portal Identification in DHCP / RA Captive-Portal Identification in DHCP / RA
draft-ietf-capport-rfc7710bis-03 draft-ietf-capport-rfc7710bis-04
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 enforcement device, and that they will need to captive-portal enforcement device, and that they will need to
authenticate to get Internet access. It is not a full solution to authenticate to get Internet access. It is not a full solution to
address all of the issues that clients may have with captive portals; address all of the issues that clients may have with captive portals;
it is designed to be used in larger solutions. The method of it is designed to be used in larger solutions. The method of
authenticating to, and interacting with the captive portal is out of authenticating to, and interacting with the captive portal is out of
scope of this document. scope of this document.
RFC7710 used DHCP code point 160. Due to a conflict, this document This document replaces RFC 7710. RFC 7710 used DHCP code point 160.
specifies TBD. Due to a conflict, this document specifies 114.
[ 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-
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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 October 1, 2020. This Internet-Draft will expire on October 30, 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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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 . . . . . . . . . . . . . . . . . . . . 5 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. Captive Portal Unrestricted Identifier . . . . . . . . . 7
4.1.1. Registry name: Captive Portal Unrestricted Identifier 6
4.2. BOOTP Vendor Extensions and DHCP Options Code Change . . 7 4.2. BOOTP Vendor Extensions and DHCP Options Code Change . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
7. Normative References . . . . . . . . . . . . . . . . . . . . 8 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 10
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 . . . . . . . . . . . . . . . 11
Appendix C. Observations From IETF 106 Network Experiment . . . 10 Appendix C. Observations From IETF 106 Network Experiment . . . 11
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.
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methods that are very similar to man-in-the-middle (MITM) attacks. methods that are very similar to man-in-the-middle (MITM) attacks.
As increasing focus is placed on security, and end nodes adopt a more As increasing focus is placed on security, and end nodes adopt a more
secure stance, these interception techniques will become less secure stance, these interception techniques will become less
effective and/or more 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 enforcement informs clients that they are behind a captive-portal enforcement
device and how to contact an API for more information. device and how to contact an API for more information.
This document replaces RFC 7710 [RFC7710].
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", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in [RFC2119]. "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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 showing the user the captive portal improve the user experience by showing the user the captive portal
information faster and more reliably. Note that, for the foreseeable information faster and more reliably. Note that, for the foreseeable
future, 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]), 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 equivalent
to reduce the chance of operational problems. The maximum length of to reduce the chance of operational problems. The maximum length of
the URI that can be carried in IPv4 DHCP is 255 bytes, so URIs longer the URI that can be carried in IPv4 DHCP is 255 bytes, so URIs longer
than 255 bytes should not be provisioned via IPv6 DHCP or IPv6 RA than 255 bytes should not be provisioned via IPv6 DHCP nor IPv6 RA
either. options.
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]. [draft-ietf-capport-api].
A captive portal server MAY redirect requests that do not have an
Accept header field ([RFC7231] Section 5.3) containing a field item
whose content-type is "application/capport+json" to the URL conveyed
in the "user-portal-url" API key. When performing such content
negotiation ([RFC7231] Section 3.4), captive portals implementors
need to keep in mind that such responses might be cached, and
therefore SHOULD include an appropriate Vary header field ([RFC7231]
Section 7.1.4) or mark them explicitly uncacheable (for example,
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. When performing such content negotiation
([RFC7231] Section 3.4), implementors of captive portals need to keep
in mind that such responses might be cached, and therefore SHOULD
include an appropriate Vary header field ([RFC7231] Section 7.1.4) or
mark them explicitly uncacheable (for example, using Cache-Control:
no-store [RFC7234] Section 5.2.2.3).
The URI SHOULD NOT contain an IP address literal. The URI SHOULD NOT contain an IP address literal. Exceptions to this
might include networks with only one operational IP address family
where DNS is either not available or not fully functional until the
captive portal has been satisfied.
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. 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 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
| code | len | URI ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+------+------+------+------+------+-- --+-----+ | Code | Len | URI (variable length) ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ...URI continued... .
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Code: The Captive-Portal DHCPv4 Option (TBD) (one octet) o Code: The Captive-Portal DHCPv4 Option (114) (one octet)
o Len: The length, 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.
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
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) .
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 unsigned 16-bit 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. See [RFC8415], Section 21.1 for more on the format of IPv6
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
bytes, so URIs longer than 255 bytes should not be provisioned via
IPv6 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 .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ .
. . . .
. . . .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Captive-Portal RA Option Format Figure 2: Captive-Portal RA Option Format
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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. 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
bytes, so URIs longer than 255 bytes should not be provisioned via
IPv6 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. It is a network one of (or indeed all of) the above options. Implementations can
configuration error if the learned URIs are not all identical. select their own precedence order (e.g., prefer one of the IPv6
options before the DHCPv4 option, or vice versa, et cetera).
However, if the URIs learned are not in fact all identical the
captive device MUST prioritize URIs learned from network provisioning
or configuration mechanisms before all other URIs. Specifically,
URIs learned via any of the options in Section 2 should take
precedence over any URI learned via some other mechanism, such as a
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. Implementations can select their own owner or administrator; it is a network configuration error if the
precedence order. 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. IETF params Registration 4.1. Captive Portal Unrestricted Identifier
4.1.1. Registry name: Captive Portal Unrestricted Identifier This document registers a new entry under the IETF URN Sub-namespace
defined in [RFC3553]:
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
is defined and therefore no sub-namespace registrations are possible. hierarchy is defined 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
Siegmund, dieter@apple.com - Reason to recover: Never published in an Siegmund, dieter@apple.com - Reason to recover: Never published in an
RFC) Tommy Pauly (Apple) and Dieter Siegmund confirm that this RFC) Tommy Pauly (Apple) and Dieter Siegmund confirm that this
codepoint hasn't been used, and Apple is willing to relinquish it for codepoint hasn't been used, and Apple is willing to relinquish it for
skipping to change at page 7, line 32 skipping to change at page 7, line 49
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 Tag: 160
Name: REMOVED/Unassigned Name: REMOVED/Unassigned
Data Length: Data Length:
Meaning: Meaning:
Reference: [RFC7710][Deprecated] Reference: [THIS-RFC][RFC7710]
5. Security Considerations 5. Security Considerations
By removing or reducing the need for captive portals to perform MITM
hijacking, this mechanism improves security by making the portal and
its actions visible, rather than hidden, and reduces the likelihood
that users will disable useful security safeguards like DNSSEC
validation, VPNs, etc. In addition, because the system knows that it
is behind a captive portal, it can know not to send cookies,
credentials, etc. By handing out a URI which is protected with TLS,
the captive portal operator can attempt to reassure the user that the
captive portal is not malicious.
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 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
skipping to change at page 8, line 19 skipping to change at page 8, line 47
performed with the presently common captive portal mechanisms, so performed with the presently common captive portal mechanisms, so
this 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
doing away with the need for interception, we think that users will
be less likely to disable useful security safeguards like DNSSEC
validation, VPNs, etc. In addition, because the system knows that it
is behind a captive portal, it can know not to send cookies,
credentials, etc. By handing out a URI which is protected with TLS,
the captive portal operator can attempt to reassure the user that the
captive portal is not malicious.
6. 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 including contributions and review from Joe Clarke, improvements including contributions and review from Joe Clarke,
Lorenzo Colitti, Dave Dolson, Hans Kuhn, Kyle Larose, Clemens Lorenzo Colitti, Dave Dolson, Hans Kuhn, Kyle Larose, Clemens
Schimpe, Martin Thompson, Michael Richardson, Remi Nguyen Van, Bernie Schimpe, Martin Thomson, Michael Richardson, Remi Nguyen Van, Subash
Volz, and Tommy Pauly. Tirupachur Comerica, Bernie Volz, and Tommy Pauly.
7. References 7. References
7.1. Normative 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, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-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>.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, [RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
C., and M. Carney, "Dynamic Host Configuration Protocol Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997,
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July <https://www.rfc-editor.org/info/rfc2132>.
2003, <https://www.rfc-editor.org/info/rfc3315>.
[RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An [RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An
IETF URN Sub-namespace for Registered Protocol IETF URN Sub-namespace for Registered Protocol
Parameters", BCP 73, RFC 3553, DOI 10.17487/RFC3553, June Parameters", BCP 73, RFC 3553, DOI 10.17487/RFC3553, June
2003, <https://www.rfc-editor.org/info/rfc3553>. 2003, <https://www.rfc-editor.org/info/rfc3553>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005, RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>. <https://www.rfc-editor.org/info/rfc3986>.
skipping to change at page 9, line 40 skipping to change at page 10, line 10
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231, Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014, DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>. <https://www.rfc-editor.org/info/rfc7231>.
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
7.2. Informative References
[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>.
7.2. URIs 7.3. URIs
[1] https://tickets.meeting.ietf.org/wiki/IETF106network#Experiments [1] https://tickets.meeting.ietf.org/wiki/IETF106network#Experiments
[2] https://tickets.meeting.ietf.org/wiki/CAPPORT [2] https://tickets.meeting.ietf.org/wiki/CAPPORT
[3] https://community.polycom.com/t5/VoIP-SIP-Phones/DHCP- [3] https://community.polycom.com/t5/VoIP-SIP-Phones/DHCP-
Standardization-160-vs-66/td-p/72577 Standardization-160-vs-66/td-p/72577
Appendix A. Changes / Author Notes. Appendix A. Changes / Author Notes.
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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. Notes that the DHCP Code changed from 160 to 114. 6. Notes that the DHCP 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].
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