Captive-Portal identification in DHCPv4 / RA
draft-wkumari-dhc-capport-08
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 7710.
|
|
|---|---|---|---|
| Authors | Warren "Ace" Kumari , Ólafur Guðmundsson , P Ebersman , Steve Sheng | ||
| Last updated | 2015-01-27 | ||
| RFC stream | (None) | ||
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draft-wkumari-dhc-capport-08
Network Working Group R. Tse
Internet-Draft N. Nicholas
Intended status: Informational J. Lau
Expires: June 11, 2018 P. Brasolin
Ribose
December 8, 2017
AsciiRFC: Authoring Internet-Drafts And RFCs Using AsciiDoc
draft-ribose-asciirfc-03
Abstract
This document describes the AsciiDoc syntax extension called AsciiRFC
designed for authoring IETF Internet-Drafts and RFCs.
AsciiDoc is a human readable document markup language which affords
more granular control over markup than comparable schemes such as
Markdown.
The AsciiRFC syntax is designed to allow the author to entirely focus
on text, providing the full power of the resulting RFC XML through
the AsciiDoc language, while abstracting away the need to manually
edit XML, including references.
This document itself was written and generated into RFC XML v2
(RFC7749) and RFC XML v3 (RFC7991) directly through asciidoctor-rfc,
an AsciiRFC generator.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 11, 2018.
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Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 5
2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5
3. Document Structure And AsciiDoctor Syntax . . . . . . . . . . 5
3.1. AsciiRFC Mapping To Asciidoctor . . . . . . . . . . . . . 7
3.2. Simple Illustration . . . . . . . . . . . . . . . . . . . 8
4. Header And Document Attributes . . . . . . . . . . . . . . . 16
4.1. Title And Basic Attributes . . . . . . . . . . . . . . . 16
4.2. Detailed Author Information . . . . . . . . . . . . . . . 17
4.3. XML Processing Information . . . . . . . . . . . . . . . 20
4.4. AsciiRFC-specific Document Attributes . . . . . . . . . . 21
5. Preamble . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6. Sections and Paragraphs . . . . . . . . . . . . . . . . . . . 25
7. Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
8. Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
8.1. Basic Lists . . . . . . . . . . . . . . . . . . . . . . . 29
8.2. List Continuation . . . . . . . . . . . . . . . . . . . . 30
9. Blockquotes . . . . . . . . . . . . . . . . . . . . . . . . . 32
10. Notes And Asides . . . . . . . . . . . . . . . . . . . . . . 33
11. Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
12. Inline Formatting . . . . . . . . . . . . . . . . . . . . . . 37
12.1. Italics, Boldface, Monospace, Subscripts, Superscripts . 37
12.2. Formatting BCP 14 Keywords . . . . . . . . . . . . . . . 37
12.3. Escaping AsciiRFC Syntax . . . . . . . . . . . . . . . . 38
13. Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
14. Cross-References . . . . . . . . . . . . . . . . . . . . . . 39
14.1. Basic Referencing . . . . . . . . . . . . . . . . . . . 39
14.2. Referencing With Attributes . . . . . . . . . . . . . . 40
15. Inclusions . . . . . . . . . . . . . . . . . . . . . . . . . 42
16. Encoding and Entities . . . . . . . . . . . . . . . . . . . . 43
17. Bibliography . . . . . . . . . . . . . . . . . . . . . . . . 44
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17.1. Using Raw RFC XML . . . . . . . . . . . . . . . . . . . 44
17.2. Preprocessing Using <spanx style="verb">asciidoctor-
bibliography</spanx> . . . . . . . . . . . . . . . . . . 46
18. RFC XML features not supported in Asciidoctor . . . . . . . . 48
19. Authoring . . . . . . . . . . . . . . . . . . . . . . . . . . 48
19.1. Using the <spanx style="verb">rfc-in-asciidoc-
template</spanx> . . . . . . . . . . . . . . . . . . . . 49
19.2. Installing AsciiRFC Backend Processors . . . . . . . . . 49
19.3. Iterating AsciiRFC Content . . . . . . . . . . . . . . . 49
20. Security Considerations . . . . . . . . . . . . . . . . . . . 50
21. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 50
22. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 50
22.1. Example 1: AsciiRFC . . . . . . . . . . . . . . . . . . 50
22.2. Example 1: RFC XML v3 . . . . . . . . . . . . . . . . . 52
22.3. Example 2: AsciiRFC . . . . . . . . . . . . . . . . . . 53
22.4. Example 2: RFC XML v3 . . . . . . . . . . . . . . . . . 59
23. References . . . . . . . . . . . . . . . . . . . . . . . . . 65
23.1. Normative References . . . . . . . . . . . . . . . . . . 65
23.2. Informative References . . . . . . . . . . . . . . . . . 65
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 67
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 67
1. Introduction
Internet-Drafts and RFCs intended for publication submission to the
IETF can be written in a multitude of formats today, including:
o XML: RFC XML v2 [RFC7749] and v3 [RFC7991]
o nroff: through "NroffEdit" [NroffEdit]
o Microsoft Word: through usage of [RFC5385]
o Lyx: through [lyx2rfc]
o Pandoc: [RFC7328], through [pandoc2rfc] or [draftr]
o Kramdown: through [kramdown-rfc2629]
o mmark: through [mmark]
Interestingly, the last three are Markdown [RFC7763] variants.
As specified in [RFC7990], the IETF intends for the canonical format
of RFCs to transition from plain-text ASCII to RFC XML v3 [RFC7991].
While plain-text will continue to be accepted from authors by the
IETF, at least in the short- to medium-term, XML will be preferred
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for submission, and any plain-text submissions will need to be
converted to RFC XML v3.
While this need is already met for RFC XML v2 [RFC7749] by the tools
specified above, the transition to RFC XML v3 [RFC7991] places added
onus on authors to generate compliant XML.
[AsciiDoc] is an alternative markup language to Markdown, with
features that make it attractive as a markup language for RFC with
XML output. This document describes the use of [Asciidoctor], a
Ruby-based enhancement of the original AsciiDoc markup language, for
RFC XML markup, with a Ruby gem written by the authors used to render
Asciidoctor documents as RFC XML. The markup language used
specifically for the purpose of generating RFC XML document is called
"AsciiRFC".
Section 1.2 of [RFC7764] famously states that "there is no such thing
as "invalid" Markdown, there is no standard demanding adherence to
the Markdown syntax, and there is no governing body that guides or
impedes its development." While there are contexts where that lack
of rigour is helpful, the authoring of RFCs does have a standard and
a governing body, and there is such a thing as invalid RFC XML. A
more rigorous counterpart to Markdown, which still preserves its
basic approach to formatting, is useful in generating RFC XML that
encompasses a fuller subset of the specification, and preempting
malformed RFC XML output.
Compared to Markdown [Asciidoctor-Manual],
o AsciiDoc was designed from the beginning as a publishing language:
it was initially intended as a plain-text alternative to the
DocBook XML schema. For that reason, Asciidoctor natively
supports the full range of formatting required by RFC XML
(including notes, tables, bibliographies, source-code blocks, and
definition lists), without resorting to embedded HTML or Markdown
"flavours"pretends" to be
whatever the user tried to access.
This technique has issues similar to the HTTP solution, but may also
break other protocols, and may expose more of the user's private
information.
3. The Captive-Portal IPv4 DHCP Option
The Captive Portal DHCP Option (TBA1) informs an IPv4 client that it
is behind a captive portal and provides the URI to access an
authentication page. This is primarily intended to improve the user
experience; for the foreseeable future (until such time that most
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systems implement this technique) captive portals will still need to
implement the interception techniques to serve legacy clients.
The format of the DHCP Captive-Portal DHCP option is shown below.
Code Len Data
+------+------+------+------+------+-- --+-----+
| code | len | URI ... |
+------+------+------+------+------+-- --+-----+
o Code: The Captive-Portal DHCP Option (TBA1)
o Len: The length, in octets of the URI.
o URI: The URI of the authentication page that the user should
connect to.
In order to avoid having to perform DNS interception, the URI SHOULD
contain an IPv4 address literal.
For cases requiring SSL/TLS (collection of billing information for
example), the IP literal can redirect to a URI containing a DNS name.
[ED NOTE: Using an address literal is less than ideal, but better
than the alternatives. Recommending a DNS name means that the CP
would need to allow DNS from unauthenticated clients (as we don't
want to force users to use the CP's provided DNS) and some users
would use this to DNS Tunnel out. This would make the CP admin block
external recursives).]
4. The Captive-Portal IPv6 RA Option
This section describes the Captive-Portal Router Advertisement
option.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | URI .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ .
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Captive-Portal RA Option Format
Type TBA2
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Length 8-bit unsigned integer. The length of the option (including
the Type and Length fields) in units of 8 bytes.
URI The URI of the authentication page that the user should connect
to. For the reasons described above, the implementer might want
to use an IP address literal instead of a DNS name. This should
be padded with NULL (0x0) to make the total option length
(including the Type and Length fields) a multiple of 8 bytes.
5. Use of the Captive-Portal Option
[ED NOTE: This option provides notice to the OS / User applications
that there is a CP. Because of differences in UI design between
Operating Systems, the exact behaviour by OS and Applications is left
to the OS vendor/Application Developer.]
The purpose of the Captive-Portal Option is to inform the operating
system and applications that they are behind a captive portal type
device and will need to authenticate before getting network access
(and how to reach the authentication page). What is done with this
information is left up to the operating system and application
vendors. This document provides a very high level example of what
could be done with this information.
Many operating systems / applications already include a "connectivity
test" to determine if they are behind a captive portal (for example,
attempting to fetch a specific URL and looking for a specific string
(such as "Success"). These tests sometimes fail or take a long time
to determine when they are behind a CP, but are usually effective for
determining that the captive portal has been satisfied. These tests
will continue to be needed, because there is currently no definitive
signal from the captive portal that it has been satisfied. [ Editor
note: It may be useful to write another document that specifies how a
client can determine that it has passed the CP. This document could
also contain advice to implmentors on only intercepting actually
needed ports, how to advertise that the CP needs to be statisfied
*again*, etc. This should not be done in this document though. ] The
connectivity test may also need to be used if the captive portal
times out the user session and needs the user to re-authenticate.
The operating system may still find the information about the captive
portal URI useful in this case.
When the device is informed that it is behind a captive portal it
should:
1. Not initiate new IP connections until the CP has been satisfied
(other than those to the captive portal browser session and
connectivity checks). Existing connections should be quiesced
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(this will happen more often than some expect -- for example, the
user purchases 1 hour of Internet at a cafe and stays there for 3
hours -- this will "interrupt" the user a few times).
2. Present a dialog box to the user informing them that they are
behind a captive portal and ask if they wish to proceed.
3. If the user elects to proceed, the device should initiate a
connection to the captive portal login page using a web browser
configured with a separate cookie store, and without a proxy
server. If there is a VPN in place, this connection should be
made outside of the VPN and the user should be informed that
connection is outside the VPN. Some captive portals send the
user a cookie when they authenticate (so that the user can re-
authenticate more easily in the future) - the browser should keep
these CP cookies separate from other cookies.
4. Once the user has authenticated, normal IP connectivity should
resume. The CP success page should contain a string, e.g
"CP_SATISFIED." The OS can then use this string to provide
further information to the user.
5. The device should (using an OS dependent method) expose to the
user / user applications that they have connected though a
captive portal (for example by creating a file in /proc/net/
containing the interface and captive portal URI). This should
continue until the network changes, or a new DHCP message without
the CP is received.
6. IANA Considerations
This document defines the DHCP Captive-Portal option and requires
assignment of an option code (TBA1) to be assigned from "Bootp and
DHCP options" registry (http://www.iana.org/assignments/ bootp-dhcp-
parameters/bootp-dhcp-parameters.xml), as specified in [RFC2939].
IANA is also requested to assign an IPv6 RA Option Type code (TBA2)
from the "IPv6 Neighbor Discovery Option Formats" registry. Thanks
IANA!
7. Security Considerations
An attacker with the ability to inject DHCP messages could include
this option and so force users to contact an address of his choosing.
As an attacker with this capability could simply list himself as the
default gateway (and so intercept all the victim's traffic), this
does not provide them with significantly more capabilities. Fake
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DHCP servers / fake RAs are currently a security concern - this
doesn't make them any better or worse.
Devices and systems that automatically connect to an open network
could potentially be tracked using the techniques described in this
document (forcing the user to continually authenticate, or exposing
their browser fingerprint.) However, similar tracking can already be
performed with the standard captive portal mechanisms, so this
technique does not give the attackers more capabilities.
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. Redirection to a portal where TLS can be used
without hijacking can ameliorate some of the implications of
connecting to a potentially malicious captive portal.
8. Acknowledgements
Thanks to Vint Cerf for the initial idea / asking me to write this.
Thanks to Wes George for supplying the IPv6 text. Thanks to Lorenzo
and Erik for the V6 RA kick in the pants.
Thanks to Fred Baker, Ted Lemon, Ole Troan and Asbjorn Tonnesen for
detailed review and comments. Also great thanks to Joel Jaeggli for
providing feedback and text.
9. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
Appendix A. Changes / Author Notes.
[RFC Editor: Please remove this section before publication ]
From 07 to 08:
o Incorporated comments from Ted Lemon. Made the document much
shorter.
o Some cleanup.
From 06 to 07:
o Incoroprated a bunch of comments from Asbjorn Tonnesen
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o Clarified that this document is only for the DHCP bits, not
everything.
o CP's *can* do HTTP redirects to DNS banes, as long as they allow
access to all needed services.
From 05 to 06:
o Integrated comments from Joel, as below
o Better introduction text, around the "kludgy hacks" section.
o Better "neither condones nor condems" text
o Fingerprint text.
o Some discussions on the v4 literal stuff.
o More Security Consideration text.
From 04 to 05:
o Integrated comments, primarily from Fred Baker.
From 03 to 04:
o Some text cleanup for readability.
o Some disclaimers about it working better on initial connection
versus CP timeout.
o Some more text explaining that CP interception is
indistinguishable from an attack.
o Connectivity Check test.
o Posting just before the draft cutoff - "I love deadlines. I love
the whooshing noise they make as they go by." -- Douglas Adams,
The Salmon of Doubt
From -02 to 03:
o Removed the DHCPv6 stuff (as suggested / requested by Erik Kline)
o Simplified / cleaned up text (I'm inclined to waffle on, then trim
the fluff)
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o This was written on a United flight with in-flight WiFi -
unfortunately I couldn't use it because their CP was borked. :-P
From -01 to 02:
o Added the IPv6 RA stuff.
From -00 to -01:
o Many nits and editorial changes.
o Whole bunch of extra text and review from Wes George on v6.
From initial to -00.
o Nothing changed in the template!
Authors' Addresses
Warren Kumari
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: warren@kumari.net
Olafur Gudmundsson
Shinkuro Inc.
4922 Fairmont Av, Suite 250
Bethesda, MD 20814
USA
Email: ogud@ogud.com
Paul Ebersman
Comcast
Email: ebersman-ietf@dragon.net
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Steve Sheng
Internet Corporation for Assigned Names and Numbers
12025 Waterfront Drive, Suite 300
Los Angeles 90094
United States of America
Phone: +1.310.301.5800
Email: steve.sheng@icann.org
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