rfc8910xml2.original.xml   rfc8910.xml 
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<rfc xmlns:xi="http://www.w3.org/2001/XInclude" category="std"
docName="draft-ietf-capport-rfc7710bis-10" number="8910"
ipr="trust200902" consensus="true"
obsoletes="7710" updates="3679" submissionType="IETF" xml:lang="en"
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<front> <front>
<!--c WK: Set long title. -->
<title abbrev="DHCP Captive-Portal">Captive-Portal Identification in DHCP <title abbrev="DHCP Captive-Portal">Captive-Portal Identification in DHCP
/ RA</title> and Router Advertisements (RAs)</title>
<seriesInfo name="RFC" value="8910"/>
<author fullname="Warren Kumari" initials="W." surname="Kumari"> <author fullname="Warren Kumari" initials="W." surname="Kumari">
<organization>Google</organization> <organization>Google</organization>
<address> <address>
<postal> <postal>
<street>1600 Amphitheatre Parkway</street> <street>1600 Amphitheatre Parkway</street>
<city>Mountain View, CA</city> <city>Mountain View, CA</city>
<code>94043</code> <code>94043</code>
<country>United States of America</country>
<country>US</country>
</postal> </postal>
<email>warren@kumari.net</email> <email>warren@kumari.net</email>
</address> </address>
</author> </author>
<author fullname="Erik Kline" initials="E." surname="Kline"> <author fullname="Erik Kline" initials="E." surname="Kline">
<organization>Loon</organization> <organization>Loon</organization>
<address> <address>
<postal> <postal>
<street>1600 Amphitheatre Parkway</street> <street>1600 Amphitheatre Parkway</street>
<city>Mountain View, CA</city> <city>Mountain View, CA</city>
<code>94043</code> <code>94043</code>
<country>United States of America</country>
<country>US</country>
</postal> </postal>
<phone/> <phone/>
<email>ek@loon.com</email> <email>ek@loon.com</email>
</address> </address>
</author> </author>
<date month="September" year="2020"/>
<date month="July" year="2020"/> <keyword>Captive Portal</keyword>
<keyword>Walled Garden</keyword>
<keyword>Coffee-shop</keyword>
<keyword>Hotel</keyword>
<abstract> <abstract>
<t>In many environments offering short-term or temporary Internet access <t>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.</t> until the user has satisfied the captive portal conditions.</t>
<t>This document describes a DHCPv4 and DHCPv6 option and a Router Adverti sement <t>This document describes a DHCPv4 and DHCPv6 option and a Router Adverti sement
(RA) option to inform clients that they are behind some sort of (RA) option to inform clients that they are behind some sort of
captive portal enforcement device, and that they will need to satify the captive portal enforcement device, and that they will need to satisfy the
Captive Portal conditions to get Captive Portal conditions to get
Internet access. It is not a full solution to address all of the issues Internet access. It is not a full solution to address all of the issues
that clients may have with captive portals; it is designed to be one that clients may have with captive portals; it is designed to be one
component of a standardized approach for hosts to interact with such component of a standardized approach for hosts to interact with such
portals. While this document defines how the network operator may convey portals. While this document defines how the network operator may convey
the captive portal API endpoint to hosts, the specific methods of the captive portal API endpoint to hosts, the specific methods of
satisfying and interacting with the captive portal are out of satisfying and interacting with the captive portal are out of
scope of this document.</t> scope of this document.</t>
<t>This document replaces RFC 7710, which used DHCP code point 160.
<t>This document replaces <xref target="RFC7710"/>. <xref target="RFC7710 Due to a conflict, this document specifies 114. Consequently, this
"/> document also updates RFC 3679.</t>
used DHCP code point 160. Due to a conflict, this document specifies 114.
Consequently, this document also updates <xref target="RFC3679"/>.</t>
</abstract> </abstract>
</front>
</front>
<middle> <middle>
<section title="Introduction"> <section numbered="true" toc="default">
<name>Introduction</name>
<t>In many environments, users need to connect to a captive portal <t>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 of billing information before they can access the Internet. Regardless of
how that mechanism operates, this document provides functionality how that mechanism operates, this document provides functionality
to allow the client to know when it is to allow the client to know when it is
behind a captive portal and how to contact it.</t> behind a captive portal and how to contact it.</t>
<t>In order to present users with the payment or AUP pages, a captive
<t>In order to present users with the payment or AUP pages, presently a portal enforcement device presently has to intercept the user's connection
captive portal enforcement device has to intercept the user's connections s and
and redirect the user to a captive portal server, using methods that are
redirect the user to a captive portal server, using methods that are very very similar to man-in-the-middle (MITM) attacks. As increasing focus is
similar to man-in-the-middle (MITM) attacks. As increasing focus is
placed on security, and end nodes adopt a more secure stance, these placed on security, and end nodes adopt a more secure stance, these
interception techniques will become less effective and/or more interception techniques will become less effective and/or more
intrusive.</t> intrusive.</t>
<t>This document describes a DHCPv4 <xref target="RFC2131" format="default
<t>This document describes a DHCPv4 <xref target="RFC2131"/> and DHCPv6 "/> and DHCPv6
<xref target="RFC8415"/> option (Captive-Portal) and an IPv6 <xref target="RFC8415" format="default"/> option (Captive-Portal) and an I
Router Advertisement (RA) <xref target="RFC4861"/> option that informs Pv6
Router Advertisement (RA) <xref target="RFC4861" format="default"/> option
that informs
clients that they are behind a captive portal enforcement device and clients that they are behind a captive portal enforcement device and
the API endpoint that the host can contact for more information.</t> the API endpoint that the host can contact for more information.</t>
<t>This document replaces RFC 7710 <xref target="RFC7710"
format="default"/>, which used DHCP code point 160. Due to a conflict,
this document specifies 114. Consequently, this document also updates
<xref target="RFC3679"/>.</t>
<section numbered="true" toc="default">
<name>Requirements Notation</name>
<t>This document replaces RFC 7710 <xref target="RFC7710"/>.</t> <t>
The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQU
<section title="Requirements Notation"> IRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
"OPTIONAL" in this document are to be interpreted as described in "<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are to
BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/> when, be interpreted as
and only when, they appear in all capitals, as shown here.</t> described in BCP&nbsp;14 <xref target="RFC2119"/> <xref target="RFC8174"/>
when, and only when, they appear in all capitals, as shown here.
</t>
</section> </section>
</section> </section>
<section anchor="option" title="The Captive-Portal Option"> <section anchor="option" numbered="true" toc="default">
<t>The Captive-Portal DHCP / RA Option informs the client that it may be <name>The Captive-Portal Option</name>
<t>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 defined behind a captive portal and provides the URI to access an API as defined
by [draft-ietf-capport-api]. This is primarily intended to improve the by <xref target="RFC8908"/>. This is primarily intended to improve the
user experience by showing the user the captive portal information faster and more user experience by showing the user the captive portal information faster and more
reliably. Note that, for the foreseeable future, captive portals will reliably. Note that, for the foreseeable future, captive portals will
still need to implement interception techniques to serve legacy still need to implement interception techniques to serve legacy
clients, and clients will need to perform probing to detect captive clients, and clients will need to perform probing to detect captive
portals"; nonetheless, the mechanism provided by this document provides portals; nonetheless, the mechanism provided by this document provides
a more reliable and performant way to do so, and is therefore the preferre d a more reliable and performant way to do so, and is therefore the preferre d
mechanism for captive portal detection.</t> mechanism for captive portal detection.</t>
<t>Clients that support the Captive Portal DHCP option <bcp14>SHOULD</bcp1
<t>Clients that support the Captive Portal DHCP option SHOULD include the 4> include the
option in the Parameter Request List in DHCPREQUEST messages. DHCP servers option in the Parameter Request List in DHCPREQUEST messages. DHCP servers
MAY send the Captive Portal option without any explicit request.</t> <bcp14>MAY</bcp14> send the Captive Portal option without any explicit req
uest.</t>
<t>In order to support multiple "classes" of clients (e.g. IPv4 only,
IPv6 only with DHCPv6 (<xref target="RFC8415"/>), and IPv6 only with RA) t
he
captive network can provision the client with the URI via multiple methods
(IPv4 DHCP, IPv6
DHCP, and IPv6 RA). The captive portal operator SHOULD ensure that the URI
s
provisioned by each method are identical to reduce the chance of operation
al problems.
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 by any of the IPv6
options described in this document. In IPv6-only environments
this restriction can be relaxed.</t>
<t>In all variants of this option, the URI MUST be that of the captive <t>In order to support multiple "classes" of clients (e.g., IPv4 only,
portal API endpoint [draft-ietf-capport-api]. IPv6 only with DHCPv6 (<xref target="RFC8415" format="default"/>), and
IPv6 only with RA), the captive network can provision the client with the
URI via multiple methods (IPv4 DHCP, IPv6 DHCP, and IPv6 RA). The
captive portal operator <bcp14>SHOULD</bcp14> ensure that the URIs
provisioned by each method are identical to reduce the chance of
operational problems. As the maximum length of the URI that can be
carried in IPv4 DHCP is 255 bytes, URIs longer than this <bcp14>SHOULD
NOT</bcp14> be provisioned by any of the IPv6 options described in this
document. In IPv6-only environments, this restriction can be
relaxed.</t>
<t>In all variants of this option, the URI <bcp14>MUST</bcp14> be that of
the captive
portal API endpoint (<xref target="RFC8908"/>).
</t> </t>
<t>A captive portal MAY do content negotiation (<xref target="RFC7231"/> <t>A captive portal <bcp14>MAY</bcp14> do content negotiation (<xref
section 3.4) and attempt to redirect clients querying without an target="RFC7231" sectionFormat="of" section="3.4"/>) and attempt to
explicit indication of support for the captive portal API content type redirect clients querying without an explicit indication of support for
(i.e. without application/capport+json listed explicitly anywhere within the captive portal API content type (i.e., without
an Accept header vis. <xref target="RFC7231"/> section 5.3). In so application/capport+json listed explicitly anywhere within an Accept
doing, the captive portal SHOULD redirect the client to the value header field as described in <xref target="RFC7231" sectionFormat="of"
associated with the "user-portal-url" API key. When performing such section="5.3"/>). In so doing, the captive portal <bcp14>SHOULD</bcp14>
content negotiation (<xref target="RFC7231"/> Section 3.4), implementors redirect the client to the value associated with the "user-portal-url"
of captive portals need to keep in mind that such responses might be API key. When performing such content negotiation (<xref
cached, and therefore SHOULD include an appropriate Vary header field target="RFC7231" sectionFormat="of" section="3.4"/>), implementors of
(<xref target="RFC7231"/> Section 7.1.4) or set the Cache-Control header captive portals need to keep in mind that such responses might be
field in any responses to "private", or a more restrictive value such as cached, and therefore <bcp14>SHOULD</bcp14> include an appropriate Vary
"no-store" <xref target="RFC7234"/> Section 5.2.2.3). header field (<xref target="RFC7231" sectionFormat="of"
section="7.1.4"/>) or set the Cache-Control header field in any
responses to "private" or a more restrictive value such as "no-store"
(<xref target="RFC7234" sectionFormat="of" section="5.2.2.3"/>).
</t> </t>
<t>The URI SHOULD NOT contain an IP address literal. Exceptions to this <t>The URI <bcp14>SHOULD NOT</bcp14> contain an IP address literal. Except ions to this
might include networks with only one operational IP address family where might include networks with only one operational IP address family where
DNS is either not available or not fully functional until the captive DNS is either not available or not fully functional until the captive
portal has been satisfied. Use of iPAddress certificates (<xref target="RF C3779"/>) portal has been satisfied. Use of IP Address certificates (<xref target="R FC3779" format="default"/>)
adds considerations that are out of scope for this document.</t> adds considerations that are out of scope for this document.</t>
<t>Networks with no captive portals may explicitly indicate this <t>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 forms of "urn:ietf:params:capport:unrestricted" may forego time-consuming forms of
captive portal detection.</t> captive portal detection.</t>
<section anchor="dhcpv4opt" numbered="true" toc="default">
<section anchor="dhcpv4opt" title="IPv4 DHCP Option"> <name>IPv4 DHCP Option</name>
<t>The format of the IPv4 Captive-Portal DHCP option is shown <t>The format of the IPv4 Captive-Portal DHCP option is shown
below.<figure> below.</t>
<artwork><![CDATA[
<figure title="Captive-Portal DHCPv4 Option Format">
<artwork name="" type="" align="left" alt=""><![CDATA[
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... .
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork> ]]></artwork>
</figure></t> </figure>
<t><list style="symbols"> <ul empty="true">
<t>Code: The Captive-Portal DHCPv4 Option (114) (one octet)</t>
<t>Len: The length (one octet), in octets, of the URI.</t> <li>
<dl>
<t>URI: The URI for the captive portal API endpoint to which the <dt>Code:
</dt>
<dd>The Captive-Portal DHCPv4 Option (114) (one octet).
</dd>
<dt>Len:
</dt>
<dd>The length (one octet), in octets, of the URI.
</dd>
<dt>URI:
</dt>
<dd>The URI for the captive portal API endpoint to which the
user should connect (encoded following the rules in <xref user should connect (encoded following the rules in <xref
target="RFC3986"/>).</t> target="RFC3986" format="default"/>).
</list>See <xref target="RFC2132"/>, Section 2 for more on the format </dd>
of IPv4 DHCP options.</t>
</dl>
</li>
</ul>
<t>See <xref target="RFC2132" sectionFormat="of" section="2"/> for more
on the format
of IPv4 DHCP options.</t>
<t>Note that the URI parameter is not null terminated.</t> <t>Note that the URI parameter is not null terminated.</t>
</section> </section>
<section anchor="dhcpv6opt" numbered="true" toc="default">
<section anchor="dhcpv6opt" title="IPv6 DHCP Option"> <name>IPv6 DHCP Option</name>
<t>The format of the IPv6 Captive-Portal DHCP option is shown below. <t>The format of the IPv6 Captive-Portal DHCP option is shown below.
<figure> </t>
<artwork><![CDATA[ <figure title="Captive-Portal DHCPv6 Option Format">
<artwork name="" type="" align="left" alt=""><![CDATA[
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) .
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork> ]]></artwork>
</figure></t> </figure>
<t><list style="symbols"> <ul empty="true">
<t>option-code: The Captive-Portal DHCPv6Option (103) (two <li>
octets)</t> <dl>
<t>option-len: The unsigned 16-bit length, in octets, of the URI. <dt>option-code:
</t> </dt>
<dd>The Captive-Portal DHCPv6 Option (103) (two octets).
</dd>
<t>URI: The URI for the captive portal API endpoint to which the <dt>option-len:
user should connect (encoded following the rules in <xref </dt>
target="RFC3986"/>).</t> <dd>The unsigned 16-bit length, in octets, of the URI.
</list>See <xref target="RFC7227"/>, Section 5.7 for more examples </dd>
of DHCP Options with URIs. See <xref target="RFC8415"/>, Section 21.1
for more on the format of IPv6 DHCP options.</t>
<t>Note that the URI parameter is not null terminated.</t> <dt>URI:
</dt>
<dd>The URI for the captive portal API endpoint to which the user should
connect (encoded following the rules in <xref target="RFC3986" format="default"/
>).
</dd>
</dl>
</li>
</ul>
<t>See <xref target="RFC7227" sectionFormat="of" section="5.7"/> for
more examples of DHCP Options with URIs. See <xref target="RFC8415"
sectionFormat="of" section="21.1"/> for more on the format of IPv6
DHCP options.</t>
<t>Note that the URI parameter is not null terminated.</t>
<t>As the maximum length of the URI that can be carried in IPv4 DHCP is <t>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 255 bytes, URIs longer than this <bcp14>SHOULD NOT</bcp14> be provisione d via
IPv6 DHCP options.</t> IPv6 DHCP options.</t>
</section> </section>
<section anchor="v6ndopt" numbered="true" toc="default">
<section anchor="v6ndopt" title="The Captive-Portal IPv6 RA Option"> <name>The Captive-Portal IPv6 RA Option</name>
<t>This section describes the Captive-Portal Router Advertisement <t>This section describes the Captive-Portal Router Advertisement
option.</t> option.</t>
<figure title="Captive-Portal RA Option Format">
<t><figure> <artwork name="" type="" align="left" alt=""><![CDATA[
<artwork><![CDATA[
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]]></artwork> ]]></artwork>
</figure></t> </figure>
<t><list style="hanging">
<t hangText="Type">37</t>
<t hangText="Length">8-bit unsigned integer. The length of the <ul empty="true">
<li>
<dl newline="false" spacing="normal">
<dt>Type:</dt>
<dd>37</dd>
<dt>Length:</dt>
<dd>8-bit unsigned integer. The length of the
option (including the Type and Length fields) in units of 8 option (including the Type and Length fields) in units of 8
bytes.</t> bytes.</dd>
<dt>URI:</dt>
<t hangText="URI">The URI for the captive portal API endpoint to <dd>The URI for the captive portal API endpoint to
which the user should connect. This MUST be padded with NUL which the user should connect. This <bcp14>MUST</bcp14> be padded wi
th NUL
(0x00) to make the total option length (including the Type and (0x00) to make the total option length (including the Type and
Length fields) a multiple of 8 bytes.</t> Length fields) a multiple of 8 bytes.</dd>
</list></t> </dl>
</li>
</ul>
<t>Note that the URI parameter is not guaranteed to be null terminated.< /t> <t>Note that the URI parameter is not guaranteed to be null terminated.< /t>
<t>As the maximum length of the URI that can be carried in IPv4 DHCP is <t>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 255 bytes, URIs longer than this <bcp14>SHOULD NOT</bcp14> be provisione d via
IPv6 RA options.</t> IPv6 RA options.</t>
</section> </section>
</section> </section>
<section anchor="precedence" numbered="true" toc="default">
<section anchor="precedence" title="Precedence of API URIs"> <name>Precedence of API URIs</name>
<t>A device may learn about Captive Portal API URIs through more than <t>A device may learn about Captive Portal API URIs through more than
one of (or indeed all of) the above options. Implementations can select one of (or indeed all of) the above options. Implementations can select
their own precedence order (e.g., prefer one of the IPv6 options before their own precedence order (e.g., prefer one of the IPv6 options before
the DHCPv4 option, or vice versa, et cetera).</t> the DHCPv4 option, or vice versa, et cetera).</t>
<t>If the URIs learned via more than one option described in <xref target=
<t>If the URIs learned via more than one option described in <xref "option" format="default"/> are not all identical, this condition should be logg
target="option"/> are not all identical, this condition should be logged ed
for the device owner or administrator; it is a network configuration error for the device owner or administrator; it is a network configuration error
if the learned URIs are not all identical.</t> if the learned URIs are not all identical.</t>
</section> </section>
<section anchor="iana" numbered="true" toc="default">
<name>IANA Considerations</name>
<section anchor="iana" title="IANA Considerations"> <t>IANA has registered a new IETF URN protocol parameter (<xref
<t>This document requests one new IETF URN protocol parameter (<xref target="RFC3553" format="default"/>). IANA has also reallocated two
target="RFC3553"/>) entry. This document also requests a reallocation DHCPv4 option codes (see <xref target="exp106" format="default"/> for
of DHCPv4 option codes (see <xref target="exp106"/> for background).</t> background) and updated the references for previously registered DHCPv6
and IPv6 ND options.</t>
<section anchor="iana-urn" numbered="true" toc="default">
<name>Captive Portal Unrestricted Identifier</name>
<t>IANA has registered a new entry in the "IETF URN Sub-namespace
for Registered Protocol Parameter Identifiers" registry defined in
<xref target="RFC3553" format="default"/>:
</t>
<dl newline="false" spacing="compact">
<dt>Registered Parameter Identifier:</dt>
<dd>capport:unrestricted</dd>
<dt>Reference:</dt>
<dd>RFC 8910</dd>
<dt>IANA Registry Reference:</dt>
<dd>RFC 8910</dd>
</dl>
<t>Only one value is defined (see URN above). No hierarchy is defined
and, therefore, no sub-namespace registrations are possible.</t>
</section>
<section anchor="ietf_dhcpv4_option_code_change" numbered="true" toc="defa
ult">
<name>BOOTP Vendor Extensions and DHCP Options Code Change</name>
<t>Thanks IANA!</t> <t>IANA has updated the "BOOTP Vendor Extensions and DHCP
Options" registry (&lt;<eref
target="https://www.iana.org/assignments/bootp-dhcp-parameters"/>&gt;)
as follows.</t>
<section anchor="iana-urn" <dl spacing="compact">
title="Captive Portal Unrestricted Identifier"> <dt>Tag:</dt>
<t>This document registers a new entry under the IETF URN <dd>114</dd>
Sub-namespace for Registered Protocol Parameter Identifiers
defined in <xref target="RFC3553"/>:
<list style="hanging">
<t hangText="Registered Parameter Identifier:">capport:unrestricted</t>
<t hangText="Reference:">RFC TBD (this document)</t>
<t hangText="IANA Registry Reference:"><xref target="RFC3553"/></t>
</list></t>
<t>Only one value is defined (see URN above). No hierarchy is defined and <dt>Name:</dt>
therefore no sub-namespace registrations are possible.</t> <dd>DHCP Captive-Portal</dd>
</section>
<section anchor="ietf_dhcpv4_option_code_change" <dt>Data Length:</dt>
title="BOOTP Vendor Extensions and DHCP Options Code Change"> <dd>N</dd>
<t>
[ RFC Ed: Please remove before publication:
RFC7710 uses DHCP Code 160 -- unfortunately, it was discovered that this o
ption 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/T
mqQz6Ma_fznD3XbhwkH9m2dB28 for more background. ]
</t>
<t>The IANA is requested to update the <dt>Meaning:</dt>
"BOOTP Vendor Extensions and DHCP Options" registry <dd>DHCP Captive-Portal</dd>
(https://www.iana.org/assignments/bootp-dhcp-parameters/bootp-dhcp-par
ameters.xhtml)
as follows.</t>
<t><figure><artwork><![CDATA[ Tag: 114 <dt>Reference:</dt>
Name: DHCP Captive-Portal <dd>RFC 8910</dd>
Data Length: N </dl>
Meaning: DHCP Captive-Portal
Reference: [THIS-RFC]]]></artwork></figure></t> <dl spacing="compact">
<dt>Tag:</dt>
<dd>160</dd>
<dt>Name:</dt>
<dd>Unassigned</dd>
<dt>Data Length:</dt>
<dd></dd>
<dt>Meaning:</dt>
<dd>Previously assigned by <xref target="RFC7710"/>; known to also be used by Po
lycom.</dd>
<dt>Reference:</dt>
<dd><xref target="RFC7710"/> RFC 8910</dd>
</dl>
<t><figure><artwork><![CDATA[ Tag: 160
Name: Unassigned
Data Length:
Meaning: Previously assigned by RFC7710; known to also be used by Polycom.
Reference: [THIS-RFC][RFC7710]]]></artwork></figure></t>
</section> </section>
<section anchor="iana_update_dhcv6_and_icmpv6" <section anchor="iana_update_dhcv6_and_icmpv6" numbered="true" toc="defaul
title="Update DHCPv6 and IPv6 ND Options Registries"> t">
<t>This document requests that the DHCPv6 and IPv6 ND options previously <name>Update DHCPv6 and IPv6 ND Options Registries</name>
registered in <xref target="RFC7710"/> be updated to reference this
<t>IANA has updated the DHCPv6 (103 - DHCP Captive-Portal) and IPv6 ND
(37 - DHCP Captive-Portal) options previously
registered in <xref target="RFC7710" format="default"/> to reference thi
s
document.</t> document.</t>
</section> </section>
</section> </section>
<section anchor="security" numbered="true" toc="default">
<section anchor="security" title="Security Considerations"> <name>Security Considerations</name>
<t>By removing or reducing the need for captive portals to perform MITM <t>By removing or reducing the need for captive portals to perform
hijacking, this mechanism improves security by making the portal and its MITM hijacking, this mechanism improves security by
actions visible, rather than hidden, and reduces the likelihood that users making the portal and its actions visible, rather than hidden, and
will disable useful security safeguards like DNSSEC validation, VPNs, etc reduces the likelihood that users will disable useful security
in order to interact with the captive portal. safeguards like DNSSEC validation, VPNs, etc. in order to interact with
In addition, because the system knows that it is behind a captive portal, the captive portal. In addition, because the system knows that it is
it can know not to send cookies, credentials, etc. By handing out a URI behind a captive portal, it can know not to send cookies, credentials,
which is protected with TLS, the captive portal operator can attempt to etc. By handing out a URI that is protected with TLS, the captive
reassure the user that the captive portal is not malicious.</t> portal operator can attempt to reassure the user that the captive portal
is not malicious.</t>
<t>Clients processing these options SHOULD validate that the option's <t>Clients processing these options <bcp14>SHOULD</bcp14> validate that th
e option's
contents conform to the validation requirements for URIs, including contents conform to the validation requirements for URIs, including
<xref target="RFC3986"/>.</t> those described in
<xref target="RFC3986" format="default"/>.</t>
<t>Each of the options described in this document is presented to a node <t>Each of the options described in this document is presented to a
using the same protocols used to provision other information critical node using the same protocols used to provision other information
to the node's successful configuration on a network. The security critical to the node's successful configuration on a network. The
considerations applicable to each of these provisioning mechanisms also security considerations applicable to each of these provisioning
apply when the node is attempting to learn the information conveyed in mechanisms also apply when the node is attempting to learn the
these options. In the absence of security measures like RA Guard information conveyed in these options. In the absence of security
(<xref target="RFC6105"/>, <xref target="RFC7113"/>) or DHCP Shield measures like RA-Guard (<xref target="RFC6105" format="default"/>, <xref
<xref target="RFC7610"/>, an attacker could inject, modify, or block DHCP target="RFC7113" format="default"/>) or DHCPv6-Shield <xref
messages or RAs.</t> target="RFC7610" format="default"/>, an attacker could inject, modify,
or block DHCP messages or RAs.</t>
<t>An attacker with the ability to inject DHCP messages or RAs <t>An attacker with the ability to inject DHCP messages or RAs
could include an option from this document to force users to contact could include an option from this document to force users to contact
an address of his choosing. As an attacker with this capability could an address of the attacker's choosing. An attacker with this capability co uld
simply list themselves as the default gateway (and so intercept all the simply list themselves 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.</t> attack.</t>
<t>However, as the operating systems and application(s) that make use of <t>However, as the operating systems and application(s) that make use of
this information know that they are connecting to a captive portal device this information know that they are connecting to a captive portal
(as opposed to intercepted connections where the OS/application may not device (as opposed to intercepted connections where the OS/application
know that they are connecting to a captive portal or hostile device) may not know that they are connecting to a captive portal or hostile
they can render the page in a device), they can render the page in a sandboxed environment and take
sandboxed environment and take other precautions, such as clearly other precautions such as clearly labeling the page as untrusted. The
labeling the page as untrusted. The means of sandboxing and user means of sandboxing and a user interface presenting this information is
interface presenting this information is not covered in this document - not covered in this document; by its nature, it is implementation
by its nature it is implementation specific and best left to the specific and best left to the application and user interface
application and user interface designers.</t> designers.</t>
<t>Devices and systems that automatically connect to an open network <t>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 Portal document (forcing the user to continually resatisfy the Captive Portal
conditions, or exposing their browser fingerprint). However, 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 attackers captive portal mechanisms, so this technique does not give the attackers
more capabilities.</t> more capabilities.</t>
<t>Captive portals are increasingly hijacking TLS connections to force <t>Captive portals are increasingly hijacking TLS connections to force
browsers to talk to the portal. Providing the portal's URI via a DHCP or browsers to talk to the portal. Providing the portal's URI via a DHCP or
RA option is a cleaner technique, and reduces user expectations of being RA option is a cleaner technique, and reduces user expectations of being
hijacked - this may improve security by making users more reluctant to hijacked; this may improve security by making users more reluctant to
accept TLS hijacking, which can be performed from beyond the network accept TLS hijacking, which can be performed from beyond the network
associated with the captive portal.</t> associated with the captive portal.</t>
</section> </section>
<section title="Acknowledgements">
<t>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.</t>
<t>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.</t>
</section>
</middle> </middle>
<back> <back>
<references title="Normative References"> <references>
<?rfc include='reference.RFC.2131'?> <name>References</name>
<references>
<?rfc include='reference.RFC.2132'?> <name>Normative References</name>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<?rfc include='reference.RFC.2119'?> FC.2131.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<?rfc include='reference.RFC.3553'?> FC.2132.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<?rfc include='reference.RFC.3986'?> FC.2119.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<?rfc include='reference.RFC.4861'?> FC.3553.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<?rfc include='reference.RFC.7227'?> FC.3986.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<?rfc include='reference.RFC.7231'?> FC.4861.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<?rfc include='reference.RFC.7234'?> FC.7227.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
<?rfc include='reference.RFC.8174'?> FC.7231.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
FC.7234.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
FC.8174.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
FC.8415.xml"/>
</references>
<references>
<name>Informative References</name>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
FC.3679.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
FC.3779.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
FC.6105.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
FC.7113.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
FC.7610.xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.R
FC.7710.xml"/>
<?rfc include='reference.RFC.8415'?> <reference anchor="RFC8908" target="https://www.rfc-editor.org/info/rfc8908">
</references> <front>
<title>Captive Portal API</title>
<author initials="T" surname="Pauly" fullname="Tommy Pauly" role="editor"
>
<organization />
</author>
<author initials="D" surname="Thakore" fullname="Darshak Thakore" role="e
ditor">
<organization />
</author>
<date month="September" year="2020" />
</front>
<seriesInfo name="RFC" value="8908" />
<seriesInfo name="DOI" value="10.17487/RFC8908"/>
</reference>
<references title="Informative References"> </references>
<?rfc include='reference.RFC.3679'?>
<?rfc include='reference.RFC.3779'?>
<?rfc include='reference.RFC.6105'?>
<?rfc include='reference.RFC.7113'?>
<?rfc include='reference.RFC.7610'?>
<?rfc include='reference.RFC.7710'?>
</references> </references>
<section title="Changes / Author Notes."> <section anchor="diff7710" numbered="true" toc="default">
<t>[RFC Editor: Please remove this section before publication ]</t> <name>Changes from RFC 7710</name>
<t>This document incorporates the following changes from <xref target="RFC
<t>From initial to -00.</t> 7710" format="default"/>.</t>
<ol spacing="normal" type="1">
<t><list style="symbols"> <li>Clarified that IP string literals are <bcp14>NOT RECOMMENDED</bcp14>
<t>Import of RFC7710.</t> .</li>
</list></t> <li>Clarified that the option URI <bcp14>MUST</bcp14> be that of the cap
tive portal
<t>From -00 to -01.</t> API endpoint.</li>
<li>Clarified that captive portals <bcp14>MAY</bcp14> do content negotia
<t><list style="symbols"> tion.</li>
<t>Remove link-relation text.</t> <li>Added text about Captive Portal API URI precedence in the event
<t>Clarify option should be in DHCPREQUEST parameter list.</t> of a network configuration error.</li>
<t>Uppercase some SHOULDs.</t> <li>Added urn:ietf:params:capport:unrestricted URN.</li>
</list></t> <li>Noted that the DHCPv4 Option Code changed from 160 to 114.</li>
</ol>
</section> </section>
<section anchor="exp106" numbered="true" toc="default">
<name>Observations from IETF 106 Network Experiment</name>
<section anchor="diff7710" title="Changes from RFC 7710"> <t>During IETF 106 in Singapore, an <eref
<t>This document incorporates the following changes from <xref target="https://tickets.meeting.ietf.org/wiki/IETF106network#Experiments">
target="RFC7710"/>.</t> experiment</eref>
enabling clients compatible with the Captive Portal API to discover a
<t><list style="numbers"> venue-info-url (see <eref
<t>Clarify that IP string literals are NOT RECOMMENDED.</t> target="https://tickets.meeting.ietf.org/wiki/CAPPORT"> experiment
description</eref> for more detail) revealed that some Polycom devices
<t>Clarify that the option URI MUST be that of the captive portal on the same network made use of DHCPv4 option code 160 for <eref
API endpoint.</t> target="https://community.polycom.com/t5/VoIP-SIP-Phones/DHCP-Standardizat
ion-160-vs-66/td-p/72577">other
<t>Clarify that captive portals MAY do content negotiation.</t> purposes</eref>.</t>
<t>The presence of DHCPv4 Option code 160 holding a value indicating the
<t>Added text about Captive Portal API URI precedence in the event Captive Portal API URL caused these devices to not function as desired.
of a network configuration error.</t> For this reason, IANA has deprecated option code 160 and
allocated a different value to be used for the Captive Portal API URL.</t>
<t>Added urn:ietf:params:capport:unrestricted URN.</t>
<t>Notes that the DHCPv4 Option Code changed from 160 to 114.</t>
</list></t>
</section> </section>
<section anchor="exp106" <section numbered="false" toc="default">
title="Observations From IETF 106 Network Experiment"> <name>Acknowledgements</name>
<t>During IETF 106 in Singapore an <eref
target="https://tickets.meeting.ietf.org/wiki/IETF106network#Experiments
"
>experiment</eref> enabling Captive Portal API compatible clients to
discover a venue-info-url (see <eref
target="https://tickets.meeting.ietf.org/wiki/CAPPORT">
experiment description</eref> for more detail) revealed that some
Polycom devices on the same network made use of DHCPv4 option code 160
for <eref
target="https://community.polycom.com/t5/VoIP-SIP-Phones/DHCP-Standardiz
ation-160-vs-66/td-p/72577"
>other purposes</eref>.</t>
<t>The presence of DHCPv4 Option code 160 holding a value indicating the <t>This document is a -bis of RFC 7710. Thanks to all of the original
Captive Portal API URL caused these devices to not function as desired. authors (<contact fullname="Warren Kumari"/>, <contact fullname="Olafur
For this reason, this document requests IANA deprecate option code 160 and Gudmundsson"/>, <contact fullname="Paul Ebersman"/>, and <contact fullname
reallocate different value to be used for the Captive Portal API URL.</t> ="Steve Sheng"/>)
and original contributors.</t>
<t>Also thanks to the CAPPORT WG for all of the discussion and
improvements, including contributions and review from <contact fullname="J
oe Clarke"/>,
<contact fullname="Lorenzo Colitti"/>, <contact fullname="Dave
Dolson"/>, <contact fullname="Hans Kuhn"/>, <contact fullname="Kyle
Larose"/>, <contact fullname="Clemens Schimpe"/>,
<contact fullname="Martin Thomson"/>, <contact fullname="Michael Richardso
n"/>,
<contact fullname="Remi Nguyen Van"/>, <contact fullname="Subash
Tirupachur Comerica"/>, <contact fullname="Bernie Volz"/>,
and <contact fullname="Tommy Pauly"/>.</t>
</section> </section>
</back> </back>
</rfc> </rfc>
 End of changes. 95 change blocks. 
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