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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'RFC2939' is mentioned on line 202, but not defined ** Obsolete normative reference: RFC 3315 (Obsoleted by RFC 8415) Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group W. Kumari 3 Internet-Draft Google 4 Intended status: Standards Track O. Gudmundsson 5 Expires: December 20, 2015 CloudFlare 6 P. Ebersman 7 Comcast 8 S. Sheng 9 ICANN 10 June 18, 2015 12 Captive-Portal Identification in DHCP / RA 13 draft-wkumari-dhc-capport-13 15 Abstract 17 In many environments offering short-term or temporary Internet access 18 (such as coffee shops), it is common to start new connections in a 19 captive portal mode. This highly restricts what the customer can do 20 until the customer has authenticated. 22 This document describes a DHCP option (and a RA extension) to inform 23 clients that they are behind some sort of captive portal device, and 24 that they will need to authenticate to get Internet Access. It is 25 not a full solution to address all of the issues that clients may 26 have with captive portals; it is designed to be used in larger 27 solutions. 29 [ Ed note (remove): This document is being developed in github: 30 https://github.com/wkumari/draft-wkumari-dhc-capport . ] 32 Status of This Memo 34 This Internet-Draft is submitted in full conformance with the 35 provisions of BCP 78 and BCP 79. 37 Internet-Drafts are working documents of the Internet Engineering 38 Task Force (IETF). Note that other groups may also distribute 39 working documents as Internet-Drafts. The list of current Internet- 40 Drafts is at http://datatracker.ietf.org/drafts/current/. 42 Internet-Drafts are draft documents valid for a maximum of six months 43 and may be updated, replaced, or obsoleted by other documents at any 44 time. It is inappropriate to use Internet-Drafts as reference 45 material or to cite them other than as "work in progress." 47 This Internet-Draft will expire on December 20, 2015. 49 Copyright Notice 51 Copyright (c) 2015 IETF Trust and the persons identified as the 52 document authors. All rights reserved. 54 This document is subject to BCP 78 and the IETF Trust's Legal 55 Provisions Relating to IETF Documents 56 (http://trustee.ietf.org/license-info) in effect on the date of 57 publication of this document. Please review these documents 58 carefully, as they describe your rights and restrictions with respect 59 to this document. Code Components extracted from this document must 60 include Simplified BSD License text as described in Section 4.e of 61 the Trust Legal Provisions and are provided without warranty as 62 described in the Simplified BSD License. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 67 1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3 68 2. The Captive-Portal Option . . . . . . . . . . . . . . . . . . 3 69 2.1. IPv4 DHCP Option . . . . . . . . . . . . . . . . . . . . 3 70 2.2. IPv6 DHCP Option . . . . . . . . . . . . . . . . . . . . 4 71 3. The Captive-Portal IPv6 RA Option . . . . . . . . . . . . . . 4 72 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 73 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 74 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 75 7. Normative References . . . . . . . . . . . . . . . . . . . . 6 76 Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 6 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 79 1. Introduction 81 In many environments, users need to connect to a captive portal 82 device and agree to an acceptable use policy (AUP) and / or provide 83 billing information before they can access the Internet. It is 84 anticipated that the IETF will work on a more fully featured protocol 85 at some point, to ease interaction with Captive Portals. Regardless 86 of how that protocol operates, it is expected that this document will 87 provide needed functionality because the client will need to know 88 when it is behind a CP and how to contact it. 90 In order to present users with the payment or AUP pages, the captive 91 portal device has to intercept the user's connections and redirect 92 the user to the captive portal, using methods that are very similar 93 to man-in-the-middle (MITM) attacks. As increasing focus is placed 94 on security, and end nodes adopt a more secure stance, these 95 interception techniques will become less effective and / or more 96 intrusive. 98 This document describe a DHCP ([RFC2131]) option (Captive Portal) and 99 an IPv6 Router Advertisement (RA) ([RFC4861]) extension that informs 100 clients that they are behind a captive portal device and how to 101 contact it. 103 1.1. Requirements notation 105 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 106 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 107 document are to be interpreted as described in [RFC2119]. 109 2. The Captive-Portal Option 111 The Captive Portal DHCP / RA Option informs the client that it is 112 behind a captive portal and provides the URI to access an 113 authentication page. This is primarily intended to improve the user 114 experience by getting them to the captive portal faster; for the 115 foreseeable future, captive portals will still need to implement the 116 interception techniques to serve legacy clients, and clients will 117 need to perform probing to detect captive portals. 119 In order to support multiple "classes" of clients (e.g: IPv4 only, 120 IPv6 only with DHCPv6([RFC3315]), IPv6 only with RA) the captive 121 portal can provide the URI via multiple methods (IPv4 DHCP, IPv6 122 DHCP, IPv6 RA). The captive portal operator should ensure that the 123 URIs handed out are equivalent to reduce the chance of operational 124 problems. 126 In order to avoid having to perform DNS interception, the URI SHOULD 127 contain an address literal, but MAY contain a DNS name if the captive 128 portal allows the client to perform DNS requests to resolve the name. 130 2.1. IPv4 DHCP Option 132 The format of the IPv4 Captive-Portal DHCP option is shown below. 134 Code Len Data 135 +------+------+------+------+------+-- --+-----+ 136 | code | len | URI ... | 137 +------+------+------+------+------+-- --+-----+ 139 o Code: The Captive-Portal DHCPv4 Option (TBA1) (one octet) 141 o Len: The length, in octets of the URI. 143 o URI: The URI of the authentication page that the user should 144 connect to. 146 2.2. IPv6 DHCP Option 148 The format of the IPv6 Captive-Portal DHCP option is shown below. 150 0 1 2 3 151 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 1 152 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 153 | option-code | option-len | 154 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 155 . URI (variable length) . 156 | ... | 157 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 159 o option-code: The Captive-Portal DHCPv6Option (TBA2) (two octets) 161 o option-len: The length, in octets of the URI. 163 o URI: The URI of the authentication page that the user should 164 connect to. 166 See [RFC7227], Section 5.7 for more examples of DHCP Options with 167 URIs. 169 3. The Captive-Portal IPv6 RA Option 171 This section describes the Captive-Portal Router Advertisement 172 option. 174 0 1 2 3 175 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 1 176 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 177 | Type | Length | URI . 178 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . 179 . . 180 . . 181 . . 182 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 183 Figure 2: Captive-Portal RA Option Format 185 Type TBA3 187 Length 8-bit unsigned integer. The length of the option (including 188 the Type and Length fields) in units of 8 bytes. 190 URI The URI of the authentication page that the user should connect 191 to. For the reasons described above, the implementer might want 192 to use an IP address literal instead of a DNS name. This should 193 be padded with NULL (0x0) to make the total option length 194 (including the Type and Length fields) a multiple of 8 bytes. 196 4. IANA Considerations 198 This document defines two DHCP Captive-Portal options, one for IPv6 199 and one for IPv6. It requires assignment of an option code (TBA1) to 200 be assigned from "Bootp and DHCP options" registry 201 (http://www.iana.org/assignments/ bootp-dhcp-parameters/bootp-dhcp- 202 parameters.xml), as specified in [RFC2939]. It also requires 203 assignment of an option code (TBA2) from the "DHCPv6 and DHCPv6 204 options" registry (http://www.iana.org/assignments/dhcpv6-parameters/ 205 dhcpv6-parameters.xml). 207 IANA is also requested to assign an IPv6 RA Option Type code (TBA3) 208 from the "IPv6 Neighbor Discovery Option Formats" registry. Thanks 209 IANA! 211 5. Security Considerations 213 An attacker with the ability to inject DHCP messages could include 214 this option and so force users to contact an address of his choosing. 215 As an attacker with this capability could simply list himself as the 216 default gateway (and so intercept all the victim's traffic); this 217 does not provide them with significantly more capabilities. Fake 218 DHCP servers / fake RAs are currently a security concern - this 219 doesn't make them any better or worse. 221 Devices and systems that automatically connect to an open network 222 could potentially be tracked using the techniques described in this 223 document (forcing the user to continually authenticate, or exposing 224 their browser fingerprint). However, similar tracking can already be 225 performed with the standard captive portal mechanisms, so this 226 technique does not give the attackers more capabilities. 228 By simplifying the interaction with the captive portal systems, and 229 doing away with the need for interception, we think that users will 230 be less likely to disable useful security safeguards like DNSSEC 231 validation, VPNs, etc. In addition, because the system knows that it 232 is behind a captive portal, it can know not to send cookies, 233 credentials, etc. Redirection to a portal where TLS can be used 234 without hijacking can ameliorate some of the implications of 235 connecting to a potentially malicious captive portal. 237 6. Acknowledgements 239 Thanks to Vint Cerf for the initial idea / asking me to write this. 240 Thanks to Wes George for supplying the IPv6 text. Thanks to Lorenzo 241 and Erik for the V6 RA kick in the pants. 243 Thanks to Fred Baker, Paul Hoffman, Ted Lemon, Martin Nilsson, Ole 244 Troan and Asbjorn Tonnesen for detailed review and comments. Also 245 great thanks to Joel Jaeggli for providing feedback and text. 247 7. Normative References 249 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 250 Requirement Levels", BCP 14, RFC 2119, March 1997. 252 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 253 2131, March 1997. 255 [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 256 and M. Carney, "Dynamic Host Configuration Protocol for 257 IPv6 (DHCPv6)", RFC 3315, July 2003. 259 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 260 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 261 September 2007. 263 [RFC7227] Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and 264 S. Krishnan, "Guidelines for Creating New DHCPv6 Options", 265 BCP 187, RFC 7227, May 2014. 267 Appendix A. Changes / Author Notes. 269 [RFC Editor: Please remove this section before publication ] 271 From 13.2 to 13(posted): 273 o Shortened the document by removing most of the [Editors notes], 274 Section 2, Section 5 and Appendix A. They were mainly background 275 and have served their purpose. This change suggested by Paul 276 Hoffman. 278 From 13.1 to 13.2: 280 o Moved all of the "what an OS could do with this info" to an 281 Appendix, to make it even clearer that this is simply an example. 283 From -12 to -13.1: 285 There was a Captive Portal Bar BoF held at the Dallas IETF meeting. 286 See https://github.com/httpwg/wiki/wiki/Captive-Portals for some 287 details. This document was discussed, and I got a fair bit of 288 feedback. Incorporating some of this in -13. 290 o "In the text discussing why a captive portal notification might be 291 useful (section 2.2 maybe?), perhaps you should say something 292 about HSTS and HTTP2.0, since they will further erode the ability 293 to use common captive portal redirection techniques." - Wes 294 George. 296 o Integrated a bunch of useful comments from Martin Nilsson 298 From -11 to -12: 300 o Integrated a whole bunch of comments from Ted Lemon, including 301 missing references, track, missing size of DHCP option, 303 From 10 to 11: 305 o Updated Olafur's affiliation. 307 From 09 to 10: 309 o Ted Lemon and Joel Jaeggli: there's no benefit to insisting on an 310 ordering. I think you should just say that the ordering is 311 indeterminate, and if different mechanisms give non-equivalent 312 answers, this is likely to cause operational problems in practice. 314 From 08 to 09: 316 o Put back the DHCPv6 option, and made the fact that is separate 317 from the DHCPv4 option clearer (Ted Lemon) 319 From 07 to 08: 321 o Incorporated comments from Ted Lemon. Made the document much 322 shorter. 324 o Some cleanup. 326 From 06 to 07: 328 o Incoroprated a bunch of comments from Asbjorn Tonnesen 330 o Clarified that this document is only for the DHCP bits, not 331 everything. 333 o CP's *can* do HTTP redirects to DNS names, as long as they allow 334 access to all needed services. 336 From 05 to 06: 338 o Integrated comments from Joel, as below 340 o Better introduction text, around the "kludgy hacks" section. 342 o Better "neither condones nor condemns" text 344 o Fingerprint text. 346 o Some discussions on the v4 literal stuff. 348 o More Security Consideration text. 350 From 04 to 05: 352 o Integrated comments, primarily from Fred Baker. 354 From 03 to 04: 356 o Some text cleanup for readability. 358 o Some disclaimers about it working better on initial connection 359 versus CP timeout. 361 o Some more text explaining that CP interception is 362 indistinguishable from an attack. 364 o Connectivity Check test. 366 o Posting just before the draft cutoff - "I love deadlines. I love 367 the whooshing noise they make as they go by." -- Douglas Adams, 368 The Salmon of Doubt 370 From -02 to 03: 372 o Removed the DHCPv6 stuff (as suggested / requested by Erik Kline) 374 o Simplified / cleaned up text (I'm inclined to waffle on, then trim 375 the fluff) 377 o This was written on a United flight with in-flight WiFi - 378 unfortunately I couldn't use it because their CP was borked. :-P 380 From -01 to 02: 382 o Added the IPv6 RA stuff. 384 From -00 to -01: 386 o Many nits and editorial changes. 388 o Whole bunch of extra text and review from Wes George on v6. 390 From initial to -00. 392 o Nothing changed in the template! 394 Authors' Addresses 396 Warren Kumari 397 Google 398 1600 Amphitheatre Parkway 399 Mountain View, CA 94043 400 US 402 Email: warren@kumari.net 404 Olafur Gudmundsson 405 CloudFlare 406 San Francisco, CA 94107 407 USA 409 Email: olafur@cloudflare.com 411 Paul Ebersman 412 Comcast 414 Email: ebersman-ietf@dragon.net 416 Steve Sheng 417 Internet Corporation for Assigned Names and Numbers 418 12025 Waterfront Drive, Suite 300 419 Los Angeles 90094 420 United States of America 422 Phone: +1.310.301.5800 423 Email: steve.sheng@icann.org