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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) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group R. Asati 3 Internet-Draft H. Singh 4 Updates: 4862, 4861, 4429 (if approved) W. Beebee 5 Intended status: Standards Track C. Pignataro 6 Expires: September 4, 2015 Cisco Systems, Inc. 7 E. Dart 8 Lawrence Berkeley National Laboratory 9 W. George 10 Time Warner Cable 11 March 3, 2015 13 Enhanced Duplicate Address Detection 14 draft-ietf-6man-enhanced-dad-14 16 Abstract 18 IPv6 Loopback Suppression and Duplicate Address Detection (DAD) are 19 discussed in Appendix A of RFC4862. That specification mentions a 20 hardware-assisted mechanism to detect looped back DAD messages. If 21 hardware cannot suppress looped back DAD messages, a software 22 solution is required. Several service provider communities have 23 expressed a need for automated detection of looped back Neighbor 24 Discovery (ND) messages used by DAD. This document includes 25 mitigation techniques and outlines the Enhanced DAD algorithm to 26 automate the detection of looped back IPv6 ND messages used by DAD. 27 For network loopback tests, the Enhanced DAD algorithm allows IPv6 to 28 self-heal after a loopback is placed and removed. Further, for 29 certain access networks the document automates resolving a specific 30 duplicate address conflict. This document updates RFC4861, RFC4862, 31 and RFC4429. 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 September 4, 2015. 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 Language . . . . . . . . . . . . . . . . . . 3 69 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 70 2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 4 71 3. Operational Mitigation Options . . . . . . . . . . . . . . . 4 72 3.1. Disable DAD on an Interface . . . . . . . . . . . . . . . 4 73 3.2. Dynamic Disable/Enable of DAD Using Layer-2 Protocol . . 5 74 3.3. Operational Considerations . . . . . . . . . . . . . . . 5 75 4. The Enhanced DAD Algorithm . . . . . . . . . . . . . . . . . 6 76 4.1. Processing Rules for Senders . . . . . . . . . . . . . . 6 77 4.2. Processing Rules for Receivers . . . . . . . . . . . . . 7 78 4.3. Changes to RFC 4861 . . . . . . . . . . . . . . . . . . . 7 79 5. Action to Perform on Detecting a Genuine Duplicate . . . . . 7 80 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 81 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 82 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 83 9. Normative References . . . . . . . . . . . . . . . . . . . . 8 84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 86 1. Introduction 88 IPv6 Loopback Suppression and Duplicate Address Detection (DAD) are 89 discussed in Appendix A of [RFC4862]. That specification mentions a 90 hardware-assisted mechanism to detect looped back DAD messages. If 91 hardware cannot suppress looped back DAD messages, a software 92 solution is required. One specific DAD message is the Neighbor 93 Solicitation (NS), specified in [RFC4861]. The NS is issued by the 94 network interface of an IPv6 node for DAD. Another message involved 95 in DAD is the Neighbor Advertisement (NA). The Enhanced DAD 96 algorithm specified in this document focuses on detecting an NS 97 looped back to the transmitting interface during the DAD operation. 99 Detecting a looped back NA does not solve the looped back DAD 100 problem. Detection of any other looped back ND messages during the 101 DAD operation is outside the scope of this document. This document 102 also includes a section on Mitigation that discusses means already 103 available to mitigate the DAD loopback problem. This document 104 updates RFC4861, RFC4862, and RFC4429. This document updates RFC 105 4862 and RFC 4429 to use the enhanced-dad algorithm to detect looped 106 back DAD probes. The Changes to RFC 4861 section includes an update 107 to RFC 4861. 109 1.1. Requirements Language 111 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 112 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 113 document are to be interpreted as described in [RFC2119]. 115 1.2. Terminology 117 o DAD-failed state - Duplication Address Detection failure as 118 specified in [RFC4862]. Note even Optimistic DAD as specified in 119 [RFC4429] can fail due to a looped back DAD probe. This document 120 covers looped back detection for Optimistic DAD as well. 122 o Looped back message - also referred to as a reflected message. 123 The message sent by the sender is received by the sender due to 124 the network or an Upper Layer Protocol on the sender looping the 125 message back. 127 o Loopback - A function in which the router's layer-3 interface (or 128 the circuit to which the router's interface is connected) is 129 looped back or connected to itself. Loopback causes packets sent 130 by the interface to be received by the interface and results in 131 interface unavailability for regular data traffic forwarding. See 132 more details in section 9.1 of [RFC2328]. The Loopback function 133 is commonly used in an interface context to gain information on 134 the quality of the interface, by employing mechanisms such as 135 ICMPv6 pings and bit-error tests. In a circuit context, this 136 function is used in wide area environments including optical Dense 137 Wave Division Multiplexing (DWDM) and SONET/SDH for fault 138 isolation (e.g. by placing a loopback at different geographic 139 locations along the path of a wide area circuit to help locate a 140 circuit fault). The Loopback function may be employed locally or 141 remotely. 143 o NS(DAD) - shorthand notation to denote an Neighbor Solicitation 144 (NS) (as specified in [RFC4861]) with unspecified IPv6 source- 145 address issued during DAD. 147 2. Problem Statement 149 Recently, service providers have reported a problem with DAD that 150 arises under the following sets of circumstances: In the first, 151 loopback testing for troubleshooting purposes is underway on a 152 circuit connected to an IPv6-enabled interface on a router. The 153 interface issues a NS for the IPv6 link-local address DAD. The NS is 154 reflected back to the router interface due to the loopback condition 155 of the circuit, and the router interface enters a DAD-failed state. 156 After the loopback condition is removed, IPv4 will return to 157 operation without further manual intervention. However, IPv6 will 158 remain in DAD-failed state until manual intervention on the router 159 restores IPv6 to operation. In the second scenario, two broadband 160 modems are served by the same service provider and terminate to the 161 same layer-3 interface on an IPv6-enabled access concentrator. In 162 this case, the two modems' Ethernet interfaces are also connected to 163 a common local network (collision domain). The access concentrator 164 serving the modems is the first-hop IPv6 router for the modems and 165 issues a NS(DAD) message for the IPv6 link-local address of its 166 layer-3 interface. The NS message reaches one modem first and this 167 modem sends the message to the local network, where the second modem 168 receives the message and then forwards it back to the access 169 concentrator. The looped back NS message causes the network 170 interface on the access concentrator to be in a DAD-failed state. 171 Such a network interface typically serves thousands of broadband 172 modems, and all would have their IPv6 connectivity affected until the 173 DAD-failed state is cleared. Additionally, it may be difficult for 174 the user of the access concentrator to determine the source of the 175 looped back DAD message. Thus in order to avoid IPv6 outages that 176 can potentially affect multiple users, there is a need for automated 177 detection of looped back NS messages during DAD operations by a node. 179 Note: In both examples above, the IPv6 link-local address DAD 180 operation fails due to a looped back DAD probe. However, the problem 181 of a looped back DAD probe exists for any IPv6 address type including 182 global addresses. 184 3. Operational Mitigation Options 186 Two mitigation options are described below that do not require any 187 change to existing implementations. 189 3.1. Disable DAD on an Interface 191 One can disable DAD on an interface so that there are no NS(DAD) 192 messages issued. While this mitigation may be the simplest, the 193 mitigation has three drawbacks: 1) care is needed when making such 194 configuration changes on point-to-point interfaces, 2) this is a one- 195 time manual configuration on each interface, and 3) genuine 196 duplicates on the link will not be detected. 198 A Service Provider router, such as an access concentrator, or network 199 core router, SHOULD support this mitigation strategy. 201 3.2. Dynamic Disable/Enable of DAD Using Layer-2 Protocol 203 Some layer-2 protocols include provisions to detect the existence of 204 a loopback on an interface circuit, usually by comparing protocol 205 data sent and received. For example, the Point-to-Point Protocol 206 (PPP) uses a magic number (section 6.4 of [RFC1661]) to detect a 207 loopback on an interface. 209 When a layer-2 protocol detects that a loopback is present on an 210 interface circuit, the device MUST temporarily disable DAD on the 211 interface. When the protocol detects that a loopback is no longer 212 present (or the interface state has changed), the device MUST 213 (re-)enable DAD on that interface. 215 This mitigation has several benefits. It leverages the layer-2 216 protocol's built-in loopback detection capability, if available. It 217 scales better since it relies on an event-driven model which requires 218 no additional state or timer. This may be significant on devices 219 with hundreds or thousands of interfaces that may be in loopback for 220 long periods of time (e.g., awaiting turn-up). 222 This solution SHOULD be enabled by default, and MUST be a 223 configurable option if the layer-2 technology provides means for 224 detecting loopback messages on an interface circuit. 226 3.3. Operational Considerations 228 The mitigation options discussed above do not require the devices on 229 both ends of the circuit to support the mitigation functionality 230 simultaneously, and do not propose any capability negotiation. They 231 are effective for unidirectional circuit or interface loopback (i.e. 232 the the loopback is placed in one direction on the circuit, rendering 233 the other direction non-operational), but they may not be effective 234 for a bidirectional loopback (i.e. the loopback is placed in both 235 directions of the circuit interface, so as to identify the faulty 236 segment). This is because unless both ends followed a mitigation 237 option specified in this document, the non-compliant device would 238 follow current behavior and disable IPv6 on that interface due to DAD 239 until manual intervention restores it. 241 4. The Enhanced DAD Algorithm 243 The Enhanced DAD algorithm covers detection of a looped back NS(DAD) 244 message. The document proposes use of a random number in the Nonce 245 Option specified in SEND [RFC3971]. Note [RFC3971] does not provide 246 a recommendation for pseudo-random functions. Pseudo-random 247 functions are covered in [RFC4086]. Since a nonce is used only once, 248 the NS(DAD) for each IPv6 address of an interface uses a different 249 nonce. Additional details of the algorithm are included in section 250 4.2. 252 If there is a collision because two nodes used the same Target 253 Address in their NS(DAD) and generated the same random nonce, then 254 the algorithm will incorrectly detect a looped back NS(DAD) when a 255 genuine address collision has occurred. Since each looped back 256 NS(DAD) event is logged to system management, the administrator of 257 the network will have access to the information necessary to 258 intervene manually. Also, because the nodes will have detected what 259 appear to be looped back NS(DAD) messages, they will continue to 260 probe, and it is unlikely that they will choose the same nonce the 261 second time (assuming quality random number generators). 263 The algorithm is capable of detecting any ND solicitation (NS and 264 Router Solicitation) or advertisement (NA and Router Advertisement) 265 that is looped back. However, there may be increased implementation 266 complexity and memory usage for the sender node to store a nonce and 267 nonce related state for all ND messages. Therefore, this document 268 does not recommend using the algorithm outside of the DAD operation 269 by an interface on a node. 271 4.1. Processing Rules for Senders 273 If a node has been configured to use the Enhanced DAD algorithm, when 274 sending an NS(DAD) for a tentative or optimistic interface address 275 the sender MUST generate a random nonce associated with the interface 276 address, MUST store the nonce internally, and MUST include the nonce 277 in the Nonce Option included in the NS(DAD). If the interface does 278 not receive any DAD failure indications within RetransTimer 279 milliseconds (see [RFC4861]) after having sent DupAddrDetectTransmits 280 Neighbor Solicitations, the interface moves the Target Address to the 281 assigned state. 283 If any probe is looped back within RetransTimer milliseconds after 284 having sent DupAddrDetectTransmits NS(DAD) messages, the interface 285 continues with another MAX_MULTICAST_SOLICIT number of NS(DAD) 286 messages transmitted RetransTimer milliseconds apart. Section 2 of 287 [RFC3971] defines a single-use nonce, so each Enhanced DAD probe uses 288 a different nonce. If no probe is looped back within RetransTimer 289 milliseconds after MAX_MULTICAST_SOLICIT NS(DAD) messages are sent, 290 the probing stops. The probing MAY be stopped via manual 291 intervention. When probing is stopped, the interface moves the 292 Target Address to the assigned state. 294 4.2. Processing Rules for Receivers 296 If the node has been configured to use the Enhanced DAD algorithm and 297 an interface on the node receives any NS(DAD) message where the 298 Target Address matches the interface address (in tentative or 299 optimistic state), the receiver compares the nonce included in the 300 message, with any stored nonce on the receiving interface. If a 301 match is found, the node SHOULD log a system management message, 302 SHOULD update any statistics counter, and MUST drop the received 303 message. If the received NS(DAD) message includes a nonce and no 304 match is found with any stored nonce, the node SHOULD log a system 305 management message for a DAD-failed state, and SHOULD update any 306 statistics counter. 308 4.3. Changes to RFC 4861 310 The following text is appended to the RetransTimer variable 311 description in section 6.3.2 of [RFC4861]: 313 The RetransTimer MAY be overridden by a link-specific document if a 314 node supports the Enhanced DAD algorithm. 316 The following text is appended to the Source Address definition in 317 section 4.3 of [RFC4861]: 319 If a node has been configured to use the Enhanced DAD algorithm, an 320 NS with an unspecified source address adds the Nonce option to the 321 message and implements the state machine of the Enhanced DAD 322 algorithm. 324 5. Action to Perform on Detecting a Genuine Duplicate 326 As described in the paragraphs above, the nonce can also serve to 327 detect genuine duplicates even when the network has potential for 328 looping back ND messages. When a genuine duplicate is detected, the 329 node follows the manual intervention specified in section 5.4.5 of 330 [RFC4862]. However, in certain cases, if the genuine duplicate 331 matches the tentative or optimistic IPv6 address of a network 332 interface of the access concentrator, additional automated action is 333 recommended. 335 Some networks follow a trust model where a trusted router serves un- 336 trusted IPv6 host nodes. Operators of such networks have a desire to 337 take automated action if a network interface of the trusted router 338 has a tentative or optimistic address duplicated by a host. One 339 example of a type of access network is cable broadband deployment 340 where the access concentrator is the first-hop IPv6 router to 341 multiple broadband modems and supports proxying of DAD messages. The 342 network interface on the access concentrator initiates DAD for an 343 IPv6 address and detects a genuine duplicate due to receiving an 344 NS(DAD) or an NA message. On detecting such a duplicate, the access 345 concentrator SHOULD log a system management message, drop the 346 received ND message, and block the modem on whose layer-2 service 347 identifier the duplicate NS(DAD) or NA message was received on. Any 348 other network that follows the same trust model MAY use the automated 349 action proposed in this section. 351 6. Security Considerations 353 This document does not improve nor reduce the security posture of 354 [RFC4862]. The nonce can be exploited by a rogue deliberately 355 changing the nonce to fail the looped back detection specified by the 356 Enhanced DAD algorithm. SEND is recommended to circumvent this 357 exploit. Additionally, the nonce does not protect against the DoS 358 caused by a rogue node replying by a fake NA to all DAD probes. SEND 359 is recommended to circumvent this exploit also. Disabling DAD has an 360 obvious security issue before a remote node on the link can issue 361 reflected NS(DAD) messages. Again, SEND is recommended for this 362 exploit. Source Address Validation Improvement (SAVI) [RFC6620] also 363 protects against various attacks by on-link rogues. 365 7. IANA Considerations 367 None. 369 8. Acknowledgements 371 Thanks (in alphabetical order by first name) to Bernie Volz, Brian 372 Haberman, Dmitry Anipko, Eric Levy-Abegnoli, Eric Vyncke, Erik 373 Nordmark, Fred Templin, Hilarie Orman, Jouni Korhonen, Michael 374 Sinatra, Ole Troan, Pascal Thubert, Ray Hunter, Suresh Krishnan, and 375 Tassos Chatzithomaoglou for their guidance and review of the 376 document. Thanks to Thomas Narten for encouraging this work. Thanks 377 to Steinar Haug and Scott Beuker for describing the use cases. 379 9. Normative References 381 [RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, 382 RFC 1661, July 1994. 384 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 385 Requirement Levels", BCP 14, RFC 2119, March 1997. 387 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. 389 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 390 Neighbor Discovery (SEND)", RFC 3971, March 2005. 392 [RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness 393 Requirements for Security", BCP 106, RFC 4086, June 2005. 395 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 396 for IPv6", RFC 4429, April 2006. 398 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 399 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 400 September 2007. 402 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 403 Address Autoconfiguration", RFC 4862, September 2007. 405 [RFC6620] Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS 406 SAVI: First-Come, First-Served Source Address Validation 407 Improvement for Locally Assigned IPv6 Addresses", RFC 408 6620, May 2012. 410 Authors' Addresses 412 Rajiv Asati 413 Cisco Systems, Inc. 414 7025 Kit Creek road 415 Research Triangle Park, NC 27709-4987 416 USA 418 Email: rajiva@cisco.com 419 URI: http://www.cisco.com/ 421 Hemant Singh 422 Cisco Systems, Inc. 423 1414 Massachusetts Ave. 424 Boxborough, MA 01719 425 USA 427 Phone: +1 978 936 1622 428 Email: shemant@cisco.com 429 URI: http://www.cisco.com/ 430 Wes Beebee 431 Cisco Systems, Inc. 432 1414 Massachusetts Ave. 433 Boxborough, MA 01719 434 USA 436 Phone: +1 978 936 2030 437 Email: wbeebee@cisco.com 438 URI: http://www.cisco.com/ 440 Carlos Pignataro 441 Cisco Systems, Inc. 442 7200-12 Kit Creek Road 443 Research Triangle Park, NC 27709 444 USA 446 Email: cpignata@cisco.com 447 URI: http://www.cisco.com/ 449 Eli Dart 450 Lawrence Berkeley National Laboratory 451 1 Cyclotron Road, Berkeley, CA 94720 452 USA 454 Email: dart@es.net 455 URI: http://www.es.net/ 457 Wesley George 458 Time Warner Cable 459 13820 Sunrise Valley Drive 460 Herndon, VA 20171 461 USA 463 Email: wesley.george@twcable.com