idnits 2.17.00 (12 Aug 2021) /tmp/idnits51998/draft-wkumari-dhc-capport-03.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 (June 1, 2014) is 2911 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- == Missing Reference: 'RFC2939' is mentioned on line 296, but not defined == Missing Reference: 'TODO' is mentioned on line 299, but not defined == Unused Reference: 'I-D.ietf-sidr-iana-objects' is defined on line 345, but no explicit reference was found in the text == Outdated reference: draft-ietf-sidr-iana-objects has been published as RFC 6491 Summary: 0 errors (**), 0 flaws (~~), 5 warnings (==), 1 comment (--).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: Informational O. Gudmundsson 5 Expires: December 3, 2014 Shinkuro Inc. 6 P. Ebersman 7 Infoblox 8 S. Sheng 9 ICANN 10 June 1, 2014 12 Captive-Portal identification in DHCP / RA 13 draft-wkumari-dhc-capport-03 15 Abstract 17 In many environments (such as hotels, coffee shops and other 18 establishments that offer Internet service to customers), it is 19 common to start new connections in a captive portal mode, i.e. highly 20 restrict what the customer can do until the customer has accepted 21 terms of service, provided payment information or authenticated. 23 This document describes a DHCP option (and an RA extension) to inform 24 clients that they are behind some sort of captive portal device, and 25 that they will need to authenticate to get Internet Access. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at http://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on December 3, 2014. 44 Copyright Notice 46 Copyright (c) 2014 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (http://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 62 1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3 63 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3 64 2.1. DNS Redirection . . . . . . . . . . . . . . . . . . . . . 3 65 2.2. HTTP Redirection . . . . . . . . . . . . . . . . . . . . 4 66 2.3. IP Hijacking . . . . . . . . . . . . . . . . . . . . . . 4 67 3. The Captive-Portal DHCP Option . . . . . . . . . . . . . . . 4 68 4. The Captive-Portal RA Option . . . . . . . . . . . . . . . . 5 69 5. Use of the Captive-Portal Option . . . . . . . . . . . . . . 6 70 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 71 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 72 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 73 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 74 9.1. Normative References . . . . . . . . . . . . . . . . . . 8 75 9.2. Informative References . . . . . . . . . . . . . . . . . 8 76 Appendix A. Changes / Author Notes. . . . . . . . . . . . . . . 8 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 79 1. Introduction 81 In many environments users need to connect to a captive portal device 82 and agree to an acceptable use policy or provide billing information 83 before they can access the Internet. 85 In order to present the user with the captive portal web page, many 86 devices perform DNS and / or HTTP and / or IP hijacks. As well as 87 being kludgy hacks, these techniques looks very similar to attacks 88 that DNSSEC and TLS protect against. This makes the user experience 89 sub-optimal. 91 This document describes a DHCP option (Captive-Portal) and IPv6 92 Router Advertisement (RA) extension that informs clients that they 93 are behind a captive portal device, and how to contact it. 95 This document neither condones nor condemns captive portals; instead 96 it recognises that they are here to stay, and attempts to improve the 97 user's experience. 99 1.1. Requirements notation 101 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 102 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 103 document are to be interpreted as described in [RFC2119]. 105 2. Background 107 Many Internet Service Providers (ISPs) that offer public Internet 108 access require the user to first accept an Acceptable Use Policy 109 (AUP) and / or provides billing information (such as their last name 110 and room number in a hotel, credit card information, etc.) through a 111 web interface. 113 In order to meet this requirement, some ISPs implement a captive 114 portal (CP) - a system that intercepts user requests and redirects 115 them to an interstitial login page. 117 Captive portals intercept and redirects user requests in a number of 118 ways, including: 120 o DNS Redirection 122 o IP Redirection 124 o HTTP Redirection 126 o Restricted scope addresses 128 o Traffic blocking (until the user is authenticated) 130 In order to ensure that the user is unable to access the Internet 131 until they have satisfied the requirements, captive portals usually 132 implement IP based filters, or place the user in to a restricted VLAN 133 (or restricted IP range) until after they have been authorized. 135 2.1. DNS Redirection 137 The CP either intercepts all DNS traffic or advertises itself (for 138 example using DHCP) as the recursive server for the network. Until 139 the user has authenticated to the captive portal, the CP responds to 140 all DNS requests listing the address of its web portal. Once the 141 user has authenticated the CP returns the "correct" addresses. 143 This technique has many shortcomings. It fails if the client is 144 performing DNSSEC validation, is running their own resolver, or 145 already has the DNS information cached. 147 2.2. HTTP Redirection 149 In this implementation, the CP acts like a transparent HTTP proxy; 150 but when it sees an HTTP request from an unauthenticated client, it 151 intercepts the request and responds with an HTTP status code 302 to 152 redirect the client to the Captive Portal Login. 154 This technique has a number of issues, including: 156 o It fails if the user is only using HTTPS. 158 o It exposes various private user information, such as HTTP Cookies, 159 etc. 161 o It doesn't work if the client has a VPN and / or proxies their web 162 traffic to an external web proxy. 164 2.3. IP Hijacking 166 In this scenario, the captive portal intercepts connections to any IP 167 address. It spoofs the destination IP address and "pretends" to be 168 whatever the user tried to access. 170 This technique has similar issues as the HTTP solution, but may also 171 break other protocols, and may expose more of the users private 172 information. 174 3. The Captive-Portal DHCP Option 176 The Captive Portal DHCP Option (TBA1) informs the DHCP client that it 177 is behind a captive portal and provides the URI to access the 178 authentication page. This is primarily intended to improve the user 179 experience; for the foreseeable future captive portals will still 180 need to implement the interception techniques to serve legacy 181 clients. 183 The format of the DHCP Captive-Portal DHCP option is shown below. 185 Code Len Data 186 +------+------+------+------+------+-- --+-----+ 187 | code | len | URI ... | 188 +------+------+------+------+------+-- --+-----+ 190 o Code: The Captive-Portal DHCP Option (TBA1 for DHCPv4, TBA2 for 191 DHCPv6) 193 o Len: The length, in octets of the URI. 195 o URI: The URI of the authentication page that the user should 196 connect to. 198 The URI MUST be a URL with an IP-literal for the host portion (to 199 remove the need to allow DNS from unauthenticated clients). The 200 DHCPv4 URI MUST contain an IPv4 address. 202 [ED NOTE: Using an address literal is less than ideal, but better 203 than the alternatives. Recommending a DNS name means that the CP 204 would need to allow DNS from unauthenticated clients (as we don't 205 want to force users to use the CP's provided DNS) and some folk would 206 use this to DNS Tunnel out. This would make the CP admin block 207 external recursives).] 209 4. The Captive-Portal RA Option 211 [ Ed: I'm far from an RA expert. I think there are only 8 bits for 212 Type, is it worth burning an option code on this? I have also 213 specified that the option length should padded to multiples of 8 byte 214 to better align with the examples I've seen. Is this required / 215 preferred, or is smaller RAs better? ] 217 This section describes the Captive-Portal Router Advertisement 218 option. 220 0 1 2 3 221 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 1 222 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 223 | Type | Length | URI . 224 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . 225 . . 226 . . 227 . . 228 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 229 Figure 2: Captive-Portal RA Option Format 231 Type TBA3 233 Length 8-bit unsigned integer. The length of the option (including 234 the Type and Length fields) in units of 8 bytes. 236 URI The URI of the authentication page that the user should connect 237 to. This should be padded with NULL (0x0) to make the total 238 option length (including the Type and Length fields) a multiple of 239 8 bytes. 241 5. Use of the Captive-Portal Option 243 [ED NOTE: This section is, and probably will remain, fairly hand 244 wavy. This option provides notice to the OS / User applications that 245 there is a CP, but I think that the UI / etc is best designed / 246 handled by the Operating System vendors / Application developers. ] 248 The purpose of the Captive-Portal Option is to inform the operating 249 system and applications that they are behind a captive portal type 250 device and will need to authenticate before getting network access 251 (and how to reach the authentication page). What is done with this 252 information is left up to the operating system and application 253 vendors. This document provides a very high level example of what 254 could be done with this information. 256 When the device discovers that it is behind a captive portal it 257 SHOULD: 259 1. Not initiate new IP connections until the CP has been satisfied 260 (other than those to the captive portal page and connectivity 261 checks). Existing connections should be quiesced (this will 262 happen more often than some expect -- you buy 1h of Internet at a 263 cafe and stay there for 3h -- this will "interrupt" you a few 264 times). 266 2. Present a dialog box to the user informing them hat they are 267 behind a captive portal and ask if they wish to proceed. 269 3. If the user elects to proceed, the device should initiate a 270 connection to the captive portal login page using a web browser 271 configured with a separate cookie store. Some captive portals 272 send the user a cookie when they authenticate (so that the user 273 can re-authenticate more easily in the future - the browser 274 should keep these CP cookies separate from other cookies. 276 4. Once the user has authenticated normal IP connectivity should 277 resume. This document does not define how to know that the user 278 has authenticated [ Ed: Should it? And option would be for the 279 "Thank you for paying" page to contain a unique string (e.g: 280 "CP_SATISFIED" ]. Operating system vendors may wish to provide a 281 public service that their devices can use as a connectivity 282 check. 284 5. The device should (using an OS dependent method) expose to the 285 user / user applications that they have connected though a 286 captive portal (for example by creating a file in /proc/net/ 287 containing the interface and captive portal URI). This should 288 continue until the network changes, or a new DHCP message without 289 the CP is received. 291 6. IANA Considerations 293 This document defines DHCPv4 Captive-Portal option which requires 294 assignment of DHCPv4 option code TBA1 assigned from "Bootp and DHCP 295 options" registry (http://www.iana.org/assignments/ bootp-dhcp- 296 parameters/bootp-dhcp-parameters.xml), as specified in [RFC2939]. 298 The IANA is also requested at assign an IPv6 RA Type code (TBA3) from 299 the [TODO] registry. Thanks IANA! 301 7. Security Considerations 303 An attacker with the ability to inject DHCP messages could include 304 this option and so force users to contact an address of his choosing. 305 As an attacker with this capability could simply list himself as the 306 default gateway (and so intercept all the victim's traffic), this 307 does not provide them with significantly more capabilities. Fake 308 DHCP servers / fake RAs are currently a security concern - this 309 doesn't make them any better or worse. 311 Devices and systems that automatically connect to open network could 312 potentially be tracked using the techniques described in this 313 document (forcing the user to continually authenticate, or exposing 314 their browser fingerprint), but similar tracking could already be 315 performed with the standard captive portal mechanisms, so this 316 doesn't seem to give the attackers more capabilities. 318 By simplifying the interaction with the captive portal systems, and 319 doing away with the need for interception, we think that users will 320 be less likely to disable useful security safeguards like DNSSEC 321 validation, VPNs, etc. In addition, because the system knows that it 322 is behind a captive portal it can know not to send cookies, 323 credentials, etc. 325 8. Acknowledgements 327 The primary author has discussed this idea with a number of folk, and 328 asked them to assist by becoming co-authors. Unfortunately he has 329 forgotten who many of them were; if you were one of them, I 330 apologize. 332 Thanks to Vint Cerf for the initial idea / asking me to write this. 333 Thanks to Wes George for supplying the v6 text. Thanks to Lorenzo 334 and Erik for the V6 RA kick in the pants. 336 9. References 338 9.1. Normative References 340 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 341 Requirement Levels", BCP 14, RFC 2119, March 1997. 343 9.2. Informative References 345 [I-D.ietf-sidr-iana-objects] 346 Manderson, T., Vegoda, L., and S. Kent, "RPKI Objects 347 issued by IANA", draft-ietf-sidr-iana-objects-03 (work in 348 progress), May 2011. 350 Appendix A. Changes / Author Notes. 352 [RFC Editor: Please remove this section before publication ] 354 From -02 to 03: 356 o Removed the DHCPv6 stuff (as suggested / requested by Erik Kline) 358 o Simplified / cleaned up text (I'm inclined to waffle on, then trim 359 the fluff) 361 o This was written on a United flight with in-flight WiFi - 362 unfortnatly I couldn't use it because their CP was borked. 364 From -01 to 02: 366 o Added the IPv6 RA stuff. 368 From -00 to -01: 370 o Many nits and editorial changes. 372 o Whole bunch of extra text and review from Wes George on v6. 374 From initial to -00. 376 o Nothing changed in the template! 378 Authors' Addresses 380 Warren Kumari 381 Google 382 1600 Amphitheatre Parkway 383 Mountain View, CA 94043 384 US 386 Email: warren@kumari.net 388 Olafur Gudmundsson 389 Shinkuro Inc. 390 4922 Fairmont Av, Suite 250 391 Bethesda, MD 20814 392 USA 394 Email: ogud@ogud.com 396 Paul Ebersman 397 Infoblox 399 Email: ebersman-ietf@dragon.net 401 Steve Sheng 402 Internet Corporation for Assigned Names and Numbers 403 12025 Waterfront Drive, Suite 300 404 Los Angeles 90094 405 United States of America 407 Phone: +1.310.301.5800 408 Email: steve.sheng@icann.org