idnits 2.17.1 draft-wkumari-dhc-capport-16.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 31, 2015) is 3161 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 208, 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: March 3, 2016 CloudFlare 6 P. Ebersman 7 Comcast 8 S. Sheng 9 ICANN 10 August 31, 2015 12 Captive-Portal Identification in DHCP / RA 13 draft-wkumari-dhc-capport-16 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 March 3, 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 2.3. The Captive-Portal IPv6 RA Option . . . . . . . . . . . . 4 73 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 74 4. Security Considerations . . . . . . . . . . . . . . . . . . . 5 75 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 76 6. Normative References . . . . . . . . . . . . . . . . . . . . 6 77 Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 7 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 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. The maximum length of the URI that can be carried in IPv4 126 DHCP is 255 byte, and so URIs longer than 255 bytes should not be 127 used in IPv6 DHCP or IPv6 RA. 129 In order to avoid having to perform DNS interception, the URI SHOULD 130 contain an address literal. If the captive portal allows the client 131 to perform DNS requests to resolve the name, it is then acceptable 132 for the URI to contain a DNS name. The URI paramter is not null 133 terminated. 135 2.1. IPv4 DHCP Option 137 The format of the IPv4 Captive-Portal DHCP option is shown below. 139 Code Len Data 140 +------+------+------+------+------+-- --+-----+ 141 | code | len | URI ... | 142 +------+------+------+------+------+-- --+-----+ 144 o Code: The Captive-Portal DHCPv4 Option (TBA1) (one octet) 146 o Len: The length, in octets of the URI. 148 o URI: The contact URI for the captive portal that the user should 149 connect to (encoded following the rules in [RFC3986]). 151 2.2. IPv6 DHCP Option 153 The format of the IPv6 Captive-Portal DHCP option is shown below. 155 0 1 2 3 156 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 1 157 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 158 | option-code | option-len | 159 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 160 . URI (variable length) . 161 | ... | 162 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 164 o option-code: The Captive-Portal DHCPv6Option (TBA2) (two octets) 166 o option-len: The length, in octets of the URI. 168 o URI: The contact URI for the captive portal that the user should 169 connect to (encoded following the rules in [RFC3986]). 171 See [RFC7227], Section 5.7 for more examples of DHCP Options with 172 URIs. 174 2.3. The Captive-Portal IPv6 RA Option 176 This section describes the Captive-Portal Router Advertisement 177 option. 179 0 1 2 3 180 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 1 181 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 182 | Type | Length | URI . 183 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . 184 . . 185 . . 186 . . 187 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 188 Figure 2: Captive-Portal RA Option Format 190 Type TBA3 192 Length 8-bit unsigned integer. The length of the option (including 193 the Type and Length fields) in units of 8 bytes. 195 URI The contact URI for the captive portal that the user should 196 connect to. For the reasons described above, the implementer 197 might want to use an IP address literal instead of a DNS name. 198 This should be padded with NULL (0x0) to make the total option 199 length (including the Type and Length fields) a multiple of 8 200 bytes. 202 3. IANA Considerations 204 This document defines two DHCP Captive-Portal options, one for IPv4 205 and one for IPv6. It requires assignment of an option code (TBA1) to 206 be assigned from "Bootp and DHCP options" registry 207 (hhttp://www.iana.org/assignments/bootp-dhcp-parameters), as 208 specified in [RFC2939]. It also requires assignment of an option 209 code (TBA2) from the "DHCPv6 and DHCPv6 options" registry 210 (http://www.iana.org/assignments/dhcpv6-parameters). 212 IANA is also requested to assign an IPv6 RA Option Type code (TBA3) 213 from the "IPv6 Neighbor Discovery Option Formats" registry. Thanks 214 IANA! 216 4. Security Considerations 218 An attacker with the ability to inject DHCP messages could include 219 this option and so force users to contact an address of his choosing. 220 As an attacker with this capability could simply list himself as the 221 default gateway (and so intercept all the victim's traffic); this 222 does not provide them with significantly more capabilities, but 223 because this document removes the need for interception, the attacker 224 may have an easier time performing the attack. As the operating 225 systems and application that make use of this information know that 226 they are connecting to a captive portal device (as opposed to 227 intercepted connections) they can render the page in a sandboxed 228 environment and take other precautions, such as clearly labeling the 229 page as untrusted. The means of sandboxing and user interface 230 presenting this information is not covered in this document - by its 231 nature it is implementation specific and best left to the application 232 and user interface designers. 234 Devices and systems that automatically connect to an open network 235 could potentially be tracked using the techniques described in this 236 document (forcing the user to continually authenticate, or exposing 237 their browser fingerprint). However, similar tracking can already be 238 performed with the standard captive portal mechanisms, so this 239 technique does not give the attackers more capabilities. 241 Captive portals are increasingly hijacking TLS connections to force > 242 browsers to talk to the portal. Providing the portal's URI via a 243 DHCP or RA option is a cleaner technique, and reduces user 244 expectations of being hijacked - this may improve security by making 245 users more reluctant to accept TLS hijacking, which can be performed 246 from beyond the network associated with the captive portal. 248 By simplifying the interaction with the captive portal systems, and 249 doing away with the need for interception, we think that users will 250 be less likely to disable useful security safeguards like DNSSEC 251 validation, VPNs, etc. In addition, because the system knows that it 252 is behind a captive portal, it can know not to send cookies, 253 credentials, etc. By handing out a URI using which is protected with 254 TLS, the captive portal operator can attempt to reassure the user 255 that the captive portal is not malicious. 257 5. Acknowledgements 259 Thanks to Vint Cerf for the initial idea / asking me to write this. 260 Thanks to Wes George for supplying the IPv6 text. Thanks to Lorenzo 261 and Erik for the V6 RA kick in the pants. 263 Thanks to Fred Baker, Paul Hoffman, Barry Leiba, Ted Lemon, Martin 264 Nilsson, Ole Troan and Asbjorn Tonnesen for detailed review and 265 comments. Thanks for David Black for review and providing text for 266 the security considerations. Also great thanks to Joel Jaeggli for 267 providing feedback and text. 269 6. Normative References 271 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 272 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 273 RFC2119, March 1997, 274 . 276 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 277 2131, DOI 10.17487/RFC2131, March 1997, 278 . 280 [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, 281 C., and M. Carney, "Dynamic Host Configuration Protocol 282 for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 283 2003, . 285 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 286 Resource Identifier (URI): Generic Syntax", STD 66, RFC 287 3986, DOI 10.17487/RFC3986, January 2005, 288 . 290 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 291 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 292 DOI 10.17487/RFC4861, September 2007, 293 . 295 [RFC7227] Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and 296 S. Krishnan, "Guidelines for Creating New DHCPv6 Options", 297 BCP 187, RFC 7227, DOI 10.17487/RFC7227, May 2014, 298 . 300 Appendix A. Changes / Author Notes. 302 [RFC Editor: Please remove this section before publication ] 304 From 15.1 to 16: 306 Incorporated (missed) comments from David Black's GenART / OpsDir 307 review. 309 From 15 to 15.1: 311 o Incorporated Brian Haberman's IESG review comment: "I think you 312 need to specify somewhere that the URIs are encoded following the 313 rules in RFC 3986." 315 From 14 to 15: 317 o Incorporated readability comment from Barry Leiba 319 From 13 to 14: 321 o Added a bunch of disclaimers explaining that this is not a 322 complete solution. We expect that the actual interaction bit 323 should be done in CAPPORT. 325 From 13.2 to 13(posted): 327 o Shortened the document by removing most of the [Editors notes], 328 Section 2, Section 5 and Appendix A. They were mainly background 329 and have served their purpose. This change suggested by Paul 330 Hoffman. 332 From 13.1 to 13.2: 334 o Moved all of the "what an OS could do with this info" to an 335 Appendix, to make it even clearer that this is simply an example. 337 From -12 to -13.1: 339 There was a Captive Portal Bar BoF held at the Dallas IETF meeting. 340 See https://github.com/httpwg/wiki/wiki/Captive-Portals for some 341 details. This document was discussed, and I got a fair bit of 342 feedback. Incorporating some of this in -13. 344 o "In the text discussing why a captive portal notification might be 345 useful (section 2.2 maybe?), perhaps you should say something 346 about HSTS and HTTP2.0, since they will further erode the ability 347 to use common captive portal redirection techniques." - Wes 348 George. 350 o Integrated a bunch of useful comments from Martin Nilsson 352 From -11 to -12: 354 o Integrated a whole bunch of comments from Ted Lemon, including 355 missing references, track, missing size of DHCP option, 357 From 10 to 11: 359 o Updated Olafur's affiliation. 361 From 09 to 10: 363 o Ted Lemon and Joel Jaeggli: there's no benefit to insisting on an 364 ordering. I think you should just say that the ordering is 365 indeterminate, and if different mechanisms give non-equivalent 366 answers, this is likely to cause operational problems in practice. 368 From 08 to 09: 370 o Put back the DHCPv6 option, and made the fact that is separate 371 from the DHCPv4 option clearer (Ted Lemon) 373 From 07 to 08: 375 o Incorporated comments from Ted Lemon. Made the document much 376 shorter. 378 o Some cleanup. 380 From 06 to 07: 382 o Incoroprated a bunch of comments from Asbjorn Tonnesen 384 o Clarified that this document is only for the DHCP bits, not 385 everything. 387 o CP's *can* do HTTP redirects to DNS names, as long as they allow 388 access to all needed services. 390 From 05 to 06: 392 o Integrated comments from Joel, as below 394 o Better introduction text, around the "kludgy hacks" section. 396 o Better "neither condones nor condemns" text 398 o Fingerprint text. 400 o Some discussions on the v4 literal stuff. 402 o More Security Consideration text. 404 From 04 to 05: 406 o Integrated comments, primarily from Fred Baker. 408 From 03 to 04: 410 o Some text cleanup for readability. 412 o Some disclaimers about it working better on initial connection 413 versus CP timeout. 415 o Some more text explaining that CP interception is 416 indistinguishable from an attack. 418 o Connectivity Check test. 420 o Posting just before the draft cutoff - "I love deadlines. I love 421 the whooshing noise they make as they go by." -- Douglas Adams, 422 The Salmon of Doubt 424 From -02 to 03: 426 o Removed the DHCPv6 stuff (as suggested / requested by Erik Kline) 428 o Simplified / cleaned up text (I'm inclined to waffle on, then trim 429 the fluff) 431 o This was written on a United flight with in-flight WiFi - 432 unfortunately I couldn't use it because their CP was borked. :-P 434 From -01 to 02: 436 o Added the IPv6 RA stuff. 438 From -00 to -01: 440 o Many nits and editorial changes. 442 o Whole bunch of extra text and review from Wes George on v6. 444 From initial to -00. 446 o Nothing changed in the template! 448 Authors' Addresses 450 Warren Kumari 451 Google 452 1600 Amphitheatre Parkway 453 Mountain View, CA 94043 454 US 456 Email: warren@kumari.net 458 Olafur Gudmundsson 459 CloudFlare 460 San Francisco, CA 94107 461 USA 463 Email: olafur@cloudflare.com 465 Paul Ebersman 466 Comcast 468 Email: ebersman-ietf@dragon.net 470 Steve Sheng 471 Internet Corporation for Assigned Names and Numbers 472 12025 Waterfront Drive, Suite 300 473 Los Angeles 90094 474 United States of America 476 Phone: +1.310.301.5800 477 Email: steve.sheng@icann.org