idnits 2.17.00 (12 Aug 2021) /tmp/idnits52795/draft-wkumari-dhc-capport-14.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (August 13, 2015) is 2473 days in the past. Is this intentional? 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 203, 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: February 14, 2016 CloudFlare 6 P. Ebersman 7 Comcast 8 S. Sheng 9 ICANN 10 August 13, 2015 12 Captive-Portal Identification in DHCP / RA 13 draft-wkumari-dhc-capport-14 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. The method of authenticating to, and interacting with the 28 captive portal is out of scope of this document. 30 [ Ed note (remove): This document is being developed in github: 31 https://github.com/wkumari/draft-wkumari-dhc-capport . ] 33 Status of This Memo 35 This Internet-Draft is submitted in full conformance with the 36 provisions of BCP 78 and BCP 79. 38 Internet-Drafts are working documents of the Internet Engineering 39 Task Force (IETF). Note that other groups may also distribute 40 working documents as Internet-Drafts. The list of current Internet- 41 Drafts is at http://datatracker.ietf.org/drafts/current/. 43 Internet-Drafts are draft documents valid for a maximum of six months 44 and may be updated, replaced, or obsoleted by other documents at any 45 time. It is inappropriate to use Internet-Drafts as reference 46 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on February 14, 2016. 50 Copyright Notice 52 Copyright (c) 2015 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (http://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 68 1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3 69 2. The Captive-Portal Option . . . . . . . . . . . . . . . . . . 3 70 2.1. IPv4 DHCP Option . . . . . . . . . . . . . . . . . . . . 3 71 2.2. IPv6 DHCP Option . . . . . . . . . . . . . . . . . . . . 4 72 3. The Captive-Portal IPv6 RA Option . . . . . . . . . . . . . . 4 73 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 74 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 75 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 76 7. Normative References . . . . . . . . . . . . . . . . . . . . 6 77 Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 6 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 80 1. Introduction 82 In many environments, users need to connect to a captive portal 83 device and agree to an acceptable use policy (AUP) and / or provide 84 billing information before they can access the Internet. It is 85 anticipated that the IETF will work on a more fully featured protocol 86 at some point, to ease interaction with Captive Portals. Regardless 87 of how that protocol operates, it is expected that this document will 88 provide needed functionality because the client will need to know 89 when it is behind a CP and how to contact it. 91 In order to present users with the payment or AUP pages, the captive 92 portal device has to intercept the user's connections and redirect 93 the user to the captive portal, using methods that are very similar 94 to man-in-the-middle (MITM) attacks. As increasing focus is placed 95 on security, and end nodes adopt a more secure stance, these 96 interception techniques will become less effective and / or more 97 intrusive. 99 This document describe a DHCP ([RFC2131]) option (Captive Portal) and 100 an IPv6 Router Advertisement (RA) ([RFC4861]) extension that informs 101 clients that they are behind a captive portal device and how to 102 contact it. 104 1.1. Requirements notation 106 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 107 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 108 document are to be interpreted as described in [RFC2119]. 110 2. The Captive-Portal Option 112 The Captive Portal DHCP / RA Option informs the client that it is 113 behind a captive portal and provides the URI to access an 114 authentication page. This is primarily intended to improve the user 115 experience by getting them to the captive portal faster; for the 116 foreseeable future, captive portals will still need to implement the 117 interception techniques to serve legacy clients, and clients will 118 need to perform probing to detect captive portals. 120 In order to support multiple "classes" of clients (e.g: IPv4 only, 121 IPv6 only with DHCPv6([RFC3315]), IPv6 only with RA) the captive 122 portal can provide the URI via multiple methods (IPv4 DHCP, IPv6 123 DHCP, IPv6 RA). The captive portal operator should ensure that the 124 URIs handed out are equivalent to reduce the chance of operational 125 problems. 127 In order to avoid having to perform DNS interception, the URI SHOULD 128 contain an address literal, but MAY contain a DNS name if the captive 129 portal allows the client to perform DNS requests to resolve the name. 131 2.1. IPv4 DHCP Option 133 The format of the IPv4 Captive-Portal DHCP option is shown below. 135 Code Len Data 136 +------+------+------+------+------+-- --+-----+ 137 | code | len | URI ... | 138 +------+------+------+------+------+-- --+-----+ 140 o Code: The Captive-Portal DHCPv4 Option (TBA1) (one octet) 142 o Len: The length, in octets of the URI. 144 o URI: The URI of the authentication page that the user should 145 connect to. 147 2.2. IPv6 DHCP Option 149 The format of the IPv6 Captive-Portal DHCP option is shown below. 151 0 1 2 3 152 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 1 153 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 154 | option-code | option-len | 155 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 156 . URI (variable length) . 157 | ... | 158 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 160 o option-code: The Captive-Portal DHCPv6Option (TBA2) (two octets) 162 o option-len: The length, in octets of the URI. 164 o URI: The URI of the authentication page that the user should 165 connect to. 167 See [RFC7227], Section 5.7 for more examples of DHCP Options with 168 URIs. 170 3. The Captive-Portal IPv6 RA Option 172 This section describes the Captive-Portal Router Advertisement 173 option. 175 0 1 2 3 176 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 1 177 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 178 | Type | Length | URI . 179 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . 180 . . 181 . . 182 . . 183 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 184 Figure 2: Captive-Portal RA Option Format 186 Type TBA3 188 Length 8-bit unsigned integer. The length of the option (including 189 the Type and Length fields) in units of 8 bytes. 191 URI The URI of the authentication page that the user should connect 192 to. For the reasons described above, the implementer might want 193 to use an IP address literal instead of a DNS name. This should 194 be padded with NULL (0x0) to make the total option length 195 (including the Type and Length fields) a multiple of 8 bytes. 197 4. IANA Considerations 199 This document defines two DHCP Captive-Portal options, one for IPv4 200 and one for IPv6. It requires assignment of an option code (TBA1) to 201 be assigned from "Bootp and DHCP options" registry 202 (hhttp://www.iana.org/assignments/bootp-dhcp-parameters), as 203 specified in [RFC2939]. It also requires assignment of an option 204 code (TBA2) from the "DHCPv6 and DHCPv6 options" registry 205 (http://www.iana.org/assignments/dhcpv6-parameters). 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, but 218 because this document removes the need for interception, the attacker 219 may have an easier time performing the attack. As the operating 220 systems and application that make use of this information know that 221 they are connecting to a captive portal device (as opposed to 222 intercepted connections) they can render the page in a sandboxed 223 environment and take other precautions, such as clearly labeling the 224 page as untrusted. The means of sandboxing and user interface 225 presenting this information is not covered in this document - by its 226 nature it is implementation specific and best left to the application 227 and user interface designers. 229 Devices and systems that automatically connect to an open network 230 could potentially be tracked using the techniques described in this 231 document (forcing the user to continually authenticate, or exposing 232 their browser fingerprint). However, similar tracking can already be 233 performed with the standard captive portal mechanisms, so this 234 technique does not give the attackers more capabilities. 236 By simplifying the interaction with the captive portal systems, and 237 doing away with the need for interception, we think that users will 238 be less likely to disable useful security safeguards like DNSSEC 239 validation, VPNs, etc. In addition, because the system knows that it 240 is behind a captive portal, it can know not to send cookies, 241 credentials, etc. Redirection to a portal where TLS can be used 242 without hijacking can ameliorate some of the implications of 243 connecting to a potentially malicious captive portal. 245 6. Acknowledgements 247 Thanks to Vint Cerf for the initial idea / asking me to write this. 248 Thanks to Wes George for supplying the IPv6 text. Thanks to Lorenzo 249 and Erik for the V6 RA kick in the pants. 251 Thanks to Fred Baker, Paul Hoffman, Ted Lemon, Martin Nilsson, Ole 252 Troan and Asbjorn Tonnesen for detailed review and comments. Also 253 great thanks to Joel Jaeggli for providing feedback and text. 255 7. Normative References 257 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 258 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 259 RFC2119, March 1997, 260 . 262 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 263 2131, DOI 10.17487/RFC2131, March 1997, 264 . 266 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 267 C., and M. Carney, "Dynamic Host Configuration Protocol 268 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 269 2003, . 271 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 272 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 273 DOI 10.17487/RFC4861, September 2007, 274 . 276 [RFC7227] Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and 277 S. Krishnan, "Guidelines for Creating New DHCPv6 Options", 278 BCP 187, RFC 7227, DOI 10.17487/RFC7227, May 2014, 279 . 281 Appendix A. Changes / Author Notes. 283 [RFC Editor: Please remove this section before publication ] 285 From 13 to 14: 287 o Added a bunch of disclaimers explaining that this is not a 288 complete solution. We expect that the actual interaction bit 289 should be done in CAPPORT. 291 From 13.2 to 13(posted): 293 o Shortened the document by removing most of the [Editors notes], 294 Section 2, Section 5 and Appendix A. They were mainly background 295 and have served their purpose. This change suggested by Paul 296 Hoffman. 298 From 13.1 to 13.2: 300 o Moved all of the "what an OS could do with this info" to an 301 Appendix, to make it even clearer that this is simply an example. 303 From -12 to -13.1: 305 There was a Captive Portal Bar BoF held at the Dallas IETF meeting. 306 See https://github.com/httpwg/wiki/wiki/Captive-Portals for some 307 details. This document was discussed, and I got a fair bit of 308 feedback. Incorporating some of this in -13. 310 o "In the text discussing why a captive portal notification might be 311 useful (section 2.2 maybe?), perhaps you should say something 312 about HSTS and HTTP2.0, since they will further erode the ability 313 to use common captive portal redirection techniques." - Wes 314 George. 316 o Integrated a bunch of useful comments from Martin Nilsson 318 From -11 to -12: 320 o Integrated a whole bunch of comments from Ted Lemon, including 321 missing references, track, missing size of DHCP option, 323 From 10 to 11: 325 o Updated Olafur's affiliation. 327 From 09 to 10: 329 o Ted Lemon and Joel Jaeggli: there's no benefit to insisting on an 330 ordering. I think you should just say that the ordering is 331 indeterminate, and if different mechanisms give non-equivalent 332 answers, this is likely to cause operational problems in practice. 334 From 08 to 09: 336 o Put back the DHCPv6 option, and made the fact that is separate 337 from the DHCPv4 option clearer (Ted Lemon) 339 From 07 to 08: 341 o Incorporated comments from Ted Lemon. Made the document much 342 shorter. 344 o Some cleanup. 346 From 06 to 07: 348 o Incoroprated a bunch of comments from Asbjorn Tonnesen 350 o Clarified that this document is only for the DHCP bits, not 351 everything. 353 o CP's *can* do HTTP redirects to DNS names, as long as they allow 354 access to all needed services. 356 From 05 to 06: 358 o Integrated comments from Joel, as below 360 o Better introduction text, around the "kludgy hacks" section. 362 o Better "neither condones nor condemns" text 364 o Fingerprint text. 366 o Some discussions on the v4 literal stuff. 368 o More Security Consideration text. 370 From 04 to 05: 372 o Integrated comments, primarily from Fred Baker. 374 From 03 to 04: 376 o Some text cleanup for readability. 378 o Some disclaimers about it working better on initial connection 379 versus CP timeout. 381 o Some more text explaining that CP interception is 382 indistinguishable from an attack. 384 o Connectivity Check test. 386 o Posting just before the draft cutoff - "I love deadlines. I love 387 the whooshing noise they make as they go by." -- Douglas Adams, 388 The Salmon of Doubt 390 From -02 to 03: 392 o Removed the DHCPv6 stuff (as suggested / requested by Erik Kline) 394 o Simplified / cleaned up text (I'm inclined to waffle on, then trim 395 the fluff) 397 o This was written on a United flight with in-flight WiFi - 398 unfortunately I couldn't use it because their CP was borked. :-P 400 From -01 to 02: 402 o Added the IPv6 RA stuff. 404 From -00 to -01: 406 o Many nits and editorial changes. 408 o Whole bunch of extra text and review from Wes George on v6. 410 From initial to -00. 412 o Nothing changed in the template! 414 Authors' Addresses 416 Warren Kumari 417 Google 418 1600 Amphitheatre Parkway 419 Mountain View, CA 94043 420 US 422 Email: warren@kumari.net 424 Olafur Gudmundsson 425 CloudFlare 426 San Francisco, CA 94107 427 USA 429 Email: olafur@cloudflare.com 430 Paul Ebersman 431 Comcast 433 Email: ebersman-ietf@dragon.net 435 Steve Sheng 436 Internet Corporation for Assigned Names and Numbers 437 12025 Waterfront Drive, Suite 300 438 Los Angeles 90094 439 United States of America 441 Phone: +1.310.301.5800 442 Email: steve.sheng@icann.org