draft-ietf-capport-rfc7710bis-11.txt   rfc8910.txt 
Network Working Group W. Kumari Internet Engineering Task Force (IETF) W. Kumari
Internet-Draft Google Request for Comments: 8910 Google
Obsoletes: 7710 (if approved) E. Kline Obsoletes: 7710 E. Kline
Updates: 3679 (if approved) Loon Updates: 3679 Loon
Intended status: Standards Track July 13, 2020 Category: Standards Track September 2020
Expires: January 14, 2021 ISSN: 2070-1721
Captive-Portal Identification in DHCP / RA Captive-Portal Identification in DHCP and Router Advertisements (RAs)
draft-ietf-capport-rfc7710bis-11
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 user can do captive portal mode. This highly restricts what the user can do
until the user has satisfied the captive portal conditions. until the user has satisfied 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
satify the Captive Portal conditions to get Internet access. It is satisfy the Captive Portal conditions to get Internet access. It is
not a full solution to address all of the issues that clients may not a full solution to address all of the issues that clients may
have with captive portals; it is designed to be one component of a have with captive portals; it is designed to be one component of a
standardized approach for hosts to interact with such portals. While standardized approach for hosts to interact with such portals. While
this document defines how the network operator may convey the captive this document defines how the network operator may convey the captive
portal API endpoint to hosts, the specific methods of satisfying and portal API endpoint to hosts, the specific methods of satisfying and
interacting with the captive portal are out of scope of this interacting with the captive portal are out of scope of this
document. document.
This document replaces [RFC7710]. [RFC7710] used DHCP code point This document replaces RFC 7710, which used DHCP code point 160. Due
160. Due to a conflict, this document specifies 114. Consequently, to a conflict, this document specifies 114. Consequently, this
this document also updates [RFC3679]. document also updates RFC 3679.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This document is a product of the Internet Engineering Task Force
Task Force (IETF). Note that other groups may also distribute (IETF). It represents the consensus of the IETF community. It has
working documents as Internet-Drafts. The list of current Internet- received public review and has been approved for publication by the
Drafts is at https://datatracker.ietf.org/drafts/current/. Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Internet-Drafts are draft documents valid for a maximum of six months Information about the current status of this document, any errata,
and may be updated, replaced, or obsoleted by other documents at any and how to provide feedback on it may be obtained at
time. It is inappropriate to use Internet-Drafts as reference https://www.rfc-editor.org/info/rfc8910.
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 14, 2021.
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
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction
1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Notation
2. The Captive-Portal Option . . . . . . . . . . . . . . . . . . 3 2. The Captive-Portal Option
2.1. IPv4 DHCP Option . . . . . . . . . . . . . . . . . . . . 4 2.1. IPv4 DHCP Option
2.2. IPv6 DHCP Option . . . . . . . . . . . . . . . . . . . . 5 2.2. IPv6 DHCP Option
2.3. The Captive-Portal IPv6 RA Option . . . . . . . . . . . . 5 2.3. The Captive-Portal IPv6 RA Option
3. Precedence of API URIs . . . . . . . . . . . . . . . . . . . 6 3. Precedence of API URIs
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 4. IANA Considerations
4.1. Captive Portal Unrestricted Identifier . . . . . . . . . 7 4.1. Captive Portal Unrestricted Identifier
4.2. BOOTP Vendor Extensions and DHCP Options Code Change . . 7 4.2. BOOTP Vendor Extensions and DHCP Options Code Change
4.3. Update DHCPv6 and IPv6 ND Options Registries . . . . . . 7 4.3. Update DHCPv6 and IPv6 ND Options Registries
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 5. Security Considerations
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 6. References
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 6.1. Normative References
7.1. Normative References . . . . . . . . . . . . . . . . . . 9 6.2. Informative References
7.2. Informative References . . . . . . . . . . . . . . . . . 10 Appendix A. Changes from RFC 7710
Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 11 Appendix B. Observations from IETF 106 Network Experiment
Appendix B. Changes from RFC 7710 . . . . . . . . . . . . . . . 12 Acknowledgements
Appendix C. Observations From IETF 106 Network Experiment . . . 12 Authors' Addresses
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
how to contact it. how to contact it.
In order to present users with the payment or AUP pages, presently a In order to present users with the payment or AUP pages, a captive
captive portal enforcement device has to intercept the user's portal enforcement device presently has to intercept the user's
connections and redirect the user to a captive portal server, using connections and redirect the user to a captive portal server, using
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 DHCPv4 [RFC2131] and DHCPv6 [RFC8415] This document describes a DHCPv4 [RFC2131] and DHCPv6 [RFC8415]
option (Captive-Portal) and an IPv6 Router Advertisement (RA) option (Captive-Portal) and an IPv6 Router Advertisement (RA)
[RFC4861] option that informs clients that they are behind a captive [RFC4861] option that informs clients that they are behind a captive
portal enforcement device and the API endpoint that the host can portal enforcement device and the API endpoint that the host can
contact for more information. contact for more information.
This document replaces RFC 7710 [RFC7710]. This document replaces RFC 7710 [RFC7710], which used DHCP code point
160. Due to a conflict, this document specifies 114. Consequently,
this document also updates [RFC3679].
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", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. 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 [RFC8908]. This is primarily intended to improve the user
improve the user experience by showing the user the captive portal experience by showing the user the captive portal information faster
information faster and more reliably. Note that, for the foreseeable and more reliably. Note that, for the foreseeable future, captive
future, captive portals will still need to implement interception portals will still need to implement interception techniques to serve
techniques to serve legacy clients, and clients will need to perform legacy clients, and clients will need to perform probing to detect
probing to detect captive portals"; nonetheless, the mechanism captive portals; nonetheless, the mechanism provided by this document
provided by this document provides a more reliable and performant way provides a more reliable and performant way to do so, and is
to do so, and is therefore the preferred mechanism for captive portal therefore the preferred mechanism for captive portal detection.
detection.
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
network can provision the client with the URI via multiple methods captive network can provision the client with the URI via multiple
(IPv4 DHCP, IPv6 DHCP, and IPv6 RA). The captive portal operator methods (IPv4 DHCP, IPv6 DHCP, and IPv6 RA). The captive portal
SHOULD ensure that the URIs provisioned by each method are identical operator SHOULD ensure that the URIs provisioned by each method are
to reduce the chance of operational problems. As the maximum length identical to reduce the chance of operational problems. As the
of the URI that can be carried in IPv4 DHCP is 255 bytes, URIs longer maximum length of the URI that can be carried in IPv4 DHCP is 255
than this SHOULD NOT be provisioned by any of the IPv6 options bytes, URIs longer than this SHOULD NOT be provisioned by any of the
described in this document. In IPv6-only environments this IPv6 options described in this document. In IPv6-only environments,
restriction can be relaxed. 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 [draft-ietf-capport-api]. portal API endpoint ([RFC8908]).
A captive portal MAY do content negotiation ([RFC7231] section 3.4) A captive portal MAY do content negotiation (Section 3.4 of
and attempt to redirect clients querying without an explicit [RFC7231]) and attempt to redirect clients querying without an
indication of support for the captive portal API content type (i.e. explicit indication of support for the captive portal API content
without application/capport+json listed explicitly anywhere within an type (i.e., without application/capport+json listed explicitly
Accept header vis. [RFC7231] section 5.3). In so doing, the captive anywhere within an Accept header field as described in Section 5.3 of
portal SHOULD redirect the client to the value associated with the [RFC7231]). In so doing, the captive portal SHOULD redirect the
"user-portal-url" API key. When performing such content negotiation client to the value associated with the "user-portal-url" API key.
([RFC7231] Section 3.4), implementors of captive portals need to keep When performing such content negotiation (Section 3.4 of [RFC7231]),
in mind that such responses might be cached, and therefore SHOULD implementors of captive portals need to keep in mind that such
include an appropriate Vary header field ([RFC7231] Section 7.1.4) or responses might be cached, and therefore SHOULD include an
set the Cache-Control header field in any responses to "private", or appropriate Vary header field (Section 7.1.4 of [RFC7231]) or set the
a more restrictive value such as "no-store" [RFC7234] Cache-Control header field in any responses to "private" or a more
Section 5.2.2.3). restrictive value such as "no-store" (Section 5.2.2.3 of [RFC7234]).
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. Use of iPAddress certificates captive portal has been satisfied. Use of IP Address certificates
([RFC3779]) adds considerations that are out of scope for this ([RFC3779]) adds considerations that are out of scope for this
document. 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
skipping to change at page 5, line 5 skipping to change at line 192
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) Figure 1: Captive-Portal DHCPv4 Option Format
o Len: The length (one octet), in octets, of the URI. Code: The Captive-Portal DHCPv4 Option (114) (one octet).
o URI: The URI for the captive portal API endpoint to which the user Len: The length (one octet), in octets, of the URI.
should connect (encoded following the rules in [RFC3986]).
See [RFC2132], Section 2 for more on the format of IPv4 DHCP options. URI: The URI for the captive portal API endpoint to which the
user should connect (encoded following the rules in [RFC3986]).
See Section 2 of [RFC2132] 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) Figure 2: Captive-Portal DHCPv6 Option Format
o option-len: The unsigned 16-bit length, in octets, of the URI. option-code: The Captive-Portal DHCPv6 Option (103) (two octets).
o URI: The URI for the captive portal API endpoint to which the user option-len: The unsigned 16-bit length, in octets, of the URI.
should connect (encoded following the rules in [RFC3986]).
See [RFC7227], Section 5.7 for more examples of DHCP Options with URI: The URI for the captive portal API endpoint to which the
URIs. See [RFC8415], Section 21.1 for more on the format of IPv6 user should connect (encoded following the rules in [RFC3986]).
See Section 5.7 of [RFC7227] for more examples of DHCP Options with
URIs. See Section 21.1 of [RFC8415] 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.
As the maximum length of the URI that can be carried in IPv4 DHCP is As the maximum length of the URI that can be carried in IPv4 DHCP is
255 bytes, URIs longer than this SHOULD NOT be provisioned via IPv6 255 bytes, URIs longer than this SHOULD NOT be provisioned via IPv6
DHCP options. DHCP options.
2.3. The Captive-Portal IPv6 RA Option 2.3. The Captive-Portal IPv6 RA Option
skipping to change at page 6, line 14 skipping to change at line 252
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
Type 37 Figure 3: Captive-Portal RA Option Format
Length 8-bit unsigned integer. The length of the option (including Type: 37
the Type and Length fields) in units of 8 bytes.
URI The URI for the captive portal API endpoint to which the user Length: 8-bit unsigned integer. The length of the option
should connect. This MUST be padded with NUL (0x00) to make the (including the Type and Length fields) in units of 8 bytes.
total option length (including the Type and Length fields) a
multiple of 8 bytes. URI: The URI for the captive portal API endpoint to which the
user should connect. This MUST be padded with NUL (0x00) to
make the total option length (including the Type and Length
fields) a 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.
As the maximum length of the URI that can be carried in IPv4 DHCP is As the maximum length of the URI that can be carried in IPv4 DHCP is
255 bytes, URIs longer than this SHOULD NOT be provisioned via IPv6 255 bytes, URIs longer than this SHOULD NOT be provisioned via 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
skipping to change at page 6, line 46 skipping to change at line 285
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 IANA has registered a new IETF URN protocol parameter ([RFC3553]).
([RFC3553]) entry. This document also requests a reallocation of IANA has also reallocated two DHCPv4 option codes (see Appendix B for
DHCPv4 option codes (see Appendix C for background). background) and updated the references for previously registered
DHCPv6 and IPv6 ND options.
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 IANA has registered a new entry in the "IETF URN Sub-namespace for
for Registered Protocol Parameter Identifiers defined in [RFC3553]: Registered Protocol Parameter Identifiers" registry defined in
[RFC3553]:
Registered Parameter Identifier: capport:unrestricted Registered Parameter Identifier: capport:unrestricted
Reference: RFC 8910
Reference: RFC TBD (this document) IANA Registry Reference: RFC 8910
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 IANA has updated the "BOOTP Vendor Extensions and DHCP Options"
160 -- unfortunately, it was discovered that this option code is registry (https://www.iana.org/assignments/bootp-dhcp-parameters) as
already widely used by Polycom (see appendix). Option 114 (URL) is follows.
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. ]
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.
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: RFC 8910
Tag: 160 Tag: 160
Name: Unassigned Name: Unassigned
Data Length: Data Length:
Meaning: Previously assigned by RFC7710; known to also be used by Polycom. Meaning: Previously assigned by [RFC7710]; known to also be used by
Reference: [THIS-RFC][RFC7710] Polycom.
Reference: [RFC7710] RFC 8910
4.3. Update DHCPv6 and IPv6 ND Options Registries 4.3. Update DHCPv6 and IPv6 ND Options Registries
This document requests that the DHCPv6 and IPv6 ND options previously IANA has updated the DHCPv6 (103 - DHCP Captive-Portal) and IPv6 ND
registered in [RFC7710] be updated to reference this document. (37 - DHCP Captive-Portal) options previously registered in [RFC7710]
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 order to interact with the captive portal. validation, VPNs, etc. in order to interact with the captive portal.
In addition, because the system knows that it is behind a captive In addition, because the system knows that it is behind a captive
portal, it can know not to send cookies, credentials, etc. By portal, it can know not to send cookies, credentials, etc. By
handing out a URI which is protected with TLS, the captive portal handing out a URI that is protected with TLS, the captive portal
operator can attempt to reassure the user that the captive portal is operator can attempt to reassure the user that the captive portal is
not malicious. not malicious.
Clients processing these options SHOULD validate that the option's Clients processing these options SHOULD validate that the option's
contents conform to the validation requirements for URIs, including contents conform to the validation requirements for URIs, including
[RFC3986]. those described in [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 DHCPv6-Shield [RFC7610], an
could inject, modify, or block DHCP messages or RAs. attacker 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 the attacker's choosing. An attacker with this capability
simply list themselves as the default gateway (and so intercept all could simply list themselves as the default gateway (and so intercept
the victim's traffic); this does not provide them with significantly all the victim's traffic); this does not provide them with
more capabilities, but because this document removes the need for significantly more capabilities, but because this document removes
interception, the attacker may have an easier time performing the the need for interception, the attacker may have an easier time
attack. performing the attack.
However, as the operating systems and application(s) 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 where the OS/ device (as opposed to intercepted connections where the OS/
application may not know that they are connecting to a captive portal application may not know that they are connecting to a captive portal
or hostile device) they can render the page in a sandboxed or hostile device), they can render the page in a sandboxed
environment and take other precautions, such as clearly labeling the environment and take other precautions such as clearly labeling the
page as untrusted. The means of sandboxing and user interface page as untrusted. The means of sandboxing and a user interface
presenting this information is not covered in this document - by its presenting this information is not covered in this document; by its
nature it is implementation specific and best left to the application nature, it is implementation specific and best left to the
and user interface designers. 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 re-satisfy the Captive document (forcing the user to continually resatisfy the Captive
Portal conditions, or exposing their browser fingerprint). However, Portal conditions or exposing their browser fingerprint). However,
similar tracking can already be performed with the presently common similar tracking can already be performed with the presently common
captive portal mechanisms, so this technique does not give the captive portal mechanisms, so this technique does not give the
attackers more capabilities. 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. References
This document is a -bis of RFC7710. Thanks to all of the original
authors (Warren Kumari, Olafur Gudmundsson, Paul Ebersman, Steve
Sheng), and original contributors.
Also thanks to the CAPPORT WG for all of the discussion and
improvements including contributions and review from Joe Clarke,
Lorenzo Colitti, Dave Dolson, Hans Kuhn, Kyle Larose, Clemens
Schimpe, Martin Thomson, Michael Richardson, Remi Nguyen Van, Subash
Tirupachur Comerica, Bernie Volz, and Tommy Pauly.
7. References
7.1. Normative References 6.1. 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>.
skipping to change at page 10, line 40 skipping to change at line 446
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
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 6.2. Informative References
[RFC3679] Droms, R., "Unused Dynamic Host Configuration Protocol [RFC3679] Droms, R., "Unused Dynamic Host Configuration Protocol
(DHCP) Option Codes", RFC 3679, DOI 10.17487/RFC3679, (DHCP) Option Codes", RFC 3679, DOI 10.17487/RFC3679,
January 2004, <https://www.rfc-editor.org/info/rfc3679>. January 2004, <https://www.rfc-editor.org/info/rfc3679>.
[RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP [RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
Addresses and AS Identifiers", RFC 3779, Addresses and AS Identifiers", RFC 3779,
DOI 10.17487/RFC3779, June 2004, DOI 10.17487/RFC3779, June 2004,
<https://www.rfc-editor.org/info/rfc3779>. <https://www.rfc-editor.org/info/rfc3779>.
skipping to change at page 11, line 25 skipping to change at line 477
[RFC7610] Gont, F., Liu, W., and G. Van de Velde, "DHCPv6-Shield: [RFC7610] Gont, F., Liu, W., and G. Van de Velde, "DHCPv6-Shield:
Protecting against Rogue DHCPv6 Servers", BCP 199, Protecting against Rogue DHCPv6 Servers", BCP 199,
RFC 7610, DOI 10.17487/RFC7610, August 2015, RFC 7610, DOI 10.17487/RFC7610, August 2015,
<https://www.rfc-editor.org/info/rfc7610>. <https://www.rfc-editor.org/info/rfc7610>.
[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>.
7.3. URIs [RFC8908] Pauly, T., Ed. and D. Thakore, Ed., "Captive Portal API",
RFC 8908, DOI 10.17487/RFC8908, September 2020,
[1] https://tickets.meeting.ietf.org/wiki/IETF106network#Experiments <https://www.rfc-editor.org/info/rfc8908>.
[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.
[RFC Editor: Please remove this section before publication ]
From initial to -00.
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 A. 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. Clarified that IP string literals are NOT RECOMMENDED.
2. Clarify that the option URI MUST be that of the captive portal 2. Clarified 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. Clarified 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 DHCPv4 Option Code changed from 160 to 114. 6. Noted that the DHCPv4 Option Code changed from 160 to 114.
Appendix C. Observations From IETF 106 Network Experiment Appendix B. Observations from IETF 106 Network Experiment
During IETF 106 in Singapore an experiment [1] enabling Captive During IETF 106 in Singapore, an experiment
Portal API compatible clients to discover a venue-info-url (see (https://tickets.meeting.ietf.org/wiki/IETF106network#Experiments)
experiment description [2] for more detail) revealed that some enabling clients compatible with the Captive Portal API to discover a
Polycom devices on the same network made use of DHCPv4 option code venue-info-url (see experiment description
160 for other purposes [3]. (https://tickets.meeting.ietf.org/wiki/CAPPORT) for more detail)
revealed that some Polycom devices on the same network made use of
DHCPv4 option code 160 for other purposes
(https://community.polycom.com/t5/VoIP-SIP-Phones/DHCP-
Standardization-160-vs-66/td-p/72577).
The presence of DHCPv4 Option code 160 holding a value indicating the The presence of DHCPv4 Option code 160 holding a value indicating the
Captive Portal API URL caused these devices to not function as Captive Portal API URL caused these devices to not function as
desired. For this reason, this document requests IANA deprecate desired. For this reason, IANA has deprecated option code 160 and
option code 160 and reallocate different value to be used for the allocated a different value to be used for the Captive Portal API
Captive Portal API URL. URL.
Acknowledgements
This document is a -bis of RFC 7710. Thanks to all of the original
authors (Warren Kumari, Olafur Gudmundsson, Paul Ebersman, and Steve
Sheng) and original contributors.
Also thanks to the CAPPORT WG for all of the discussion and
improvements, including contributions and review from Joe Clarke,
Lorenzo Colitti, Dave Dolson, Hans Kuhn, Kyle Larose, Clemens
Schimpe, Martin Thomson, Michael Richardson, Remi Nguyen Van, Subash
Tirupachur Comerica, Bernie Volz, and Tommy Pauly.
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 United States of America
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 United States of America
Email: ek@loon.com Email: ek@loon.com
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