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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: August 10, 2015 Cisco Systems, Inc. 7 E. Dart 8 Lawrence Berkeley National Laboratory 9 W. George 10 Time Warner Cable 11 February 6, 2015 13 Enhanced Duplicate Address Detection 14 draft-ietf-6man-enhanced-dad-13 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 August 10, 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. 106 1.1. Requirements Language 108 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 109 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 110 document are to be interpreted as described in [RFC2119]. 112 1.2. Terminology 114 o DAD-failed state - Duplication Address Detection failure as 115 specified in [RFC4862]. Note even Optimistic DAD as specified in 116 [RFC4429] can fail due to a looped back DAD probe. This document 117 covers looped back detection for Optimistic DAD as well. 119 o Looped back message - also referred to as a reflected message. 120 The message sent by the sender is received by the sender due to 121 the network or an Upper Layer Protocol on the sender looping the 122 message back. 124 o Loopback - A function in which the router's layer-3 interface (or 125 the circuit to which the router's interface is connected) is 126 looped back or connected to itself. Loopback causes packets sent 127 by the interface to be received by the interface and results in 128 interface unavailability for regular data traffic forwarding. See 129 more details in section 9.1 of [RFC2328]. The Loopback function 130 is commonly used in an interface context to gain information on 131 the quality of the interface, by employing mechanisms such as 132 ICMPv6 pings and bit-error tests. In a circuit context, this 133 function is used in wide area environments including optical Dense 134 Wave Division Multiplexing (DWDM) and SONET/SDH for fault 135 isolation (e.g. by placing a loopback at different geographic 136 locations along the path of a wide area circuit to help locate a 137 circuit fault). The Loopback function may be employed locally or 138 remotely. 140 o NS(DAD) - shorthand notation to denote an Neighbor Solicitation 141 (NS) (as specified in [RFC4861]) with unspecified IPv6 source- 142 address issued during DAD. 144 2. Problem Statement 146 Recently, service providers have reported a problem with DAD that 147 arises under the following sets of circumstances: In the first, 148 loopback testing for troubleshooting purposes is underway on a 149 circuit connected to an IPv6-enabled interface on a router. The 150 interface issues a NS for the IPv6 link-local address DAD. The NS is 151 reflected back to the router interface due to the loopback condition 152 of the circuit, and the router interface enters a DAD-failed state. 153 After the loopback condition is removed, IPv4 will return to 154 operation without further manual intervention. However, IPv6 will 155 remain in DAD-failed state until manual intervention on the router 156 restores IPv6 to operation. In the second scenario, two broadband 157 modems are served by the same service provider and terminate to the 158 same layer-3 interface on an IPv6-enabled access concentrator. In 159 this case, the two modems' Ethernet interfaces are also connected to 160 a common local network (collision domain). The access concentrator 161 serving the modems is the first-hop IPv6 router for the modems and 162 issues a NS(DAD) message for the IPv6 link-local address of its 163 layer-3 interface. The NS message reaches one modem first and this 164 modem sends the message to the local network, where the second modem 165 receives the message and then forwards it back to the access 166 concentrator. The looped back NS message causes the network 167 interface on the access concentrator to be in a DAD-failed state. 168 Such a network interface typically serves thousands of broadband 169 modems, and all would have their IPv6 connectivity affected until the 170 DAD-failed state is cleared. Additionally, it may be difficult for 171 the user of the access concentrator to determine the source of the 172 looped back DAD message. Thus in order to avoid IPv6 outages that 173 can potentially affect multiple users, there is a need for automated 174 detection of looped back NS messages during DAD operations by a node. 176 Note: In both examples above, the IPv6 link-local address DAD 177 operation fails due to a looped back DAD probe. However, the problem 178 of a looped back DAD probe exists for any IPv6 address type including 179 global addresses. 181 3. Operational Mitigation Options 183 Two mitigation options are described below that do not require any 184 change to existing implementations. 186 3.1. Disable DAD on an Interface 188 One can disable DAD on an interface so that there are no NS(DAD) 189 messages issued. While this mitigation may be the simplest, the 190 mitigation has three drawbacks: 1) care is needed when making such 191 configuration changes on point-to-point interfaces, 2) this is a one- 192 time manual configuration on each interface, and 3) genuine 193 duplicates on the link will not be detected. 195 A Service Provider router, such as an access concentrator, or network 196 core router, SHOULD support this mitigation strategy. 198 3.2. Dynamic Disable/Enable of DAD Using Layer-2 Protocol 200 Some layer-2 protocols include provisions to detect the existence of 201 a loopback on an interface circuit, usually by comparing protocol 202 data sent and received. For example, the Point-to-Point Protocol 203 (PPP) uses a magic number (section 6.4 of [RFC1661]) to detect a 204 loopback on an interface. 206 When a layer-2 protocol detects that a loopback is present on an 207 interface circuit, the device MUST temporarily disable DAD on the 208 interface. When the protocol detects that a loopback is no longer 209 present (or the interface state has changed), the device MUST 210 (re-)enable DAD on that interface. 212 This mitigation has several benefits. It leverages the layer-2 213 protocol's built-in loopback detection capability, if available. It 214 scales better since it relies on an event-driven model which requires 215 no additional state or timer. This may be significant on devices 216 with hundreds or thousands of interfaces that may be in loopback for 217 long periods of time (e.g., awaiting turn-up). 219 This solution SHOULD be enabled by default, and MUST be a 220 configurable option if the layer-2 technology provides means for 221 detecting loopback messages on an interface circuit. 223 3.3. Operational Considerations 225 The mitigation options discussed above do not require the devices on 226 both ends of the circuit to support the mitigation functionality 227 simultaneously, and do not propose any capability negotiation. They 228 are effective for unidirectional circuit or interface loopback (i.e. 229 the the loopback is placed in one direction on the circuit, rendering 230 the other direction non-operational), but they may not be effective 231 for a bidirectional loopback (i.e. the loopback is placed in both 232 directions of the circuit interface, so as to identify the faulty 233 segment). This is because unless both ends followed a mitigation 234 option specified in this document, the non-compliant device would 235 follow current behavior and disable IPv6 on that interface due to DAD 236 until manual intervention restores it. 238 4. The Enhanced DAD Algorithm 240 The Enhanced DAD algorithm covers detection of a looped back NS(DAD) 241 message. The document proposes use of a random number in the Nonce 242 Option specified in SEND [RFC3971]. Note [RFC3971] does not provide 243 a recommendation for pseudo-random functions. Pseudo-random 244 functions are covered in [RFC4086]. Since a nonce is used only once, 245 the NS(DAD) for each IPv6 address of an interface uses a different 246 nonce. Additional details of the algorithm are included in section 247 4.2. 249 If there is a collision because two nodes used the same Target 250 Address in their NS(DAD) and generated the same random nonce, then 251 the algorithm will incorrectly detect a looped back NS(DAD) when a 252 genuine address collision has occurred. Since each looped back 253 NS(DAD) event is logged to system management, the administrator of 254 the network will have access to the information necessary to 255 intervene manually. Also, because the nodes will have detected what 256 appear to be looped back NS(DAD) messages, they will continue to 257 probe, and it is unlikely that they will choose the same nonce the 258 second time (assuming quality random number generators). 260 The algorithm is capable of detecting any ND solicitation (NS and 261 Router Solicitation) or advertisement (NA and Router Advertisement) 262 that is looped back. However, there may be increased implementation 263 complexity and memory usage for the sender node to store a nonce and 264 nonce related state for all ND messages. Therefore, this document 265 does not recommend using the algorithm outside of the DAD operation 266 by an interface on a node. 268 4.1. Processing Rules for Senders 270 If a node has been configured to use the Enhanced DAD algorithm, when 271 sending an NS(DAD) for a tentative or optimistic interface address 272 the sender MUST generate a random nonce associated with the interface 273 address, MUST store the nonce internally, and MUST include the nonce 274 in the Nonce Option included in the NS(DAD). If the interface does 275 not receive any DAD failure indications within RetransTimer 276 milliseconds (see [RFC4861]) after having sent DupAddrDetectTransmits 277 Neighbor Solicitations, the interface moves the Target Address to the 278 assigned state. 280 If any probe is looped back within RetransTimer milliseconds after 281 having sent DupAddrDetectTransmits NS(DAD) messages, the interface 282 continues with another MAX_MULTICAST_SOLICIT number of NS(DAD) 283 messages transmitted RetransTimer milliseconds apart. Section 2 of 284 [RFC3971] defines a single-use nonce, so each Enhanced DAD probe uses 285 a different nonce. If no probe is looped back within RetransTimer 286 milliseconds after MAX_MULTICAST_SOLICIT NS(DAD) messages are sent, 287 the probing stops. The probing MAY be stopped via manual 288 intervention. When probing is stopped, the interface moves the 289 Target Address to the assigned state. 291 4.2. Processing Rules for Receivers 293 If the node has been configured to use the Enhanced DAD algorithm and 294 an interface on the node receives any NS(DAD) message where the 295 Target Address matches the interface address (in tentative or 296 optimistic state), the receiver compares the nonce included in the 297 message, with any stored nonce on the receiving interface. If a 298 match is found, the node SHOULD log a system management message, 299 SHOULD update any statistics counter, and MUST drop the received 300 message. If the received NS(DAD) message includes a nonce and no 301 match is found with any stored nonce, the node SHOULD log a system 302 management message for a DAD-failed state, and SHOULD update any 303 statistics counter. 305 4.3. Changes to RFC 4861 307 The following text is appended to the RetransTimer variable 308 description in section 6.3.2 of [RFC4861]: 310 The RetransTimer MAY be overridden by a link-specific document if a 311 node supports the Enhanced DAD algorithm. 313 The following text is appended to the Source Address definition in 314 section 4.3 of [RFC4861]: 316 If a node has been configured to use the Enhanced DAD algorithm, an 317 NS with an unspecified source address adds the Nonce option to the 318 message and implements the state machine of the Enhanced DAD 319 algorithm. 321 5. Action to Perform on Detecting a Genuine Duplicate 323 As described in the paragraphs above, the nonce can also serve to 324 detect genuine duplicates even when the network has potential for 325 looping back ND messages. When a genuine duplicate is detected, the 326 node follows the manual intervention specified in section 5.4.5 of 327 [RFC4862]. However, in certain cases, if the genuine duplicate 328 matches the tentative or optimistic IPv6 address of a network 329 interface of the access concentrator, additional automated action is 330 recommended. 332 Some networks follow a trust model where a trusted router serves un- 333 trusted IPv6 host nodes. Operators of such networks have a desire to 334 take automated action if a network interface of the trusted router 335 has a tentative or optimistic address duplicated by a host. One 336 example of a type of access network is cable broadband deployment 337 where the access concentrator is the first-hop IPv6 router to 338 multiple broadband modems and supports proxying of DAD messages. The 339 network interface on the access concentrator initiates DAD for an 340 IPv6 address and detects a genuine duplicate due to receiving an 341 NS(DAD) or an NA message. On detecting such a duplicate, the access 342 concentrator SHOULD log a system management message, drop the 343 received ND message, and block the modem on whose layer-2 service 344 identifier the duplicate NS(DAD) or NA message was received on. Any 345 other network that follows the same trust model MAY use the automated 346 action proposed in this section. 348 6. Security Considerations 350 This document does not improve nor reduce the security posture of 351 [RFC4862]. The nonce can be exploited by a rogue deliberately 352 changing the nonce to fail the looped back detection specified by the 353 Enhanced DAD algorithm. SEND is recommended to circumvent this 354 exploit. Additionally, the nonce does not protect against the DoS 355 caused by a rogue node replying by a fake NA to all DAD probes. SEND 356 is recommended to circumvent this exploit also. Disabling DAD has an 357 obvious security issue before a remote node on the link can issue 358 reflected NS(DAD) messages. Again, SEND is recommended for this 359 exploit. Source Address Validation Improvement (SAVI) [RFC6620] also 360 protects against various attacks by on-link rogues. 362 7. IANA Considerations 364 None. 366 8. Acknowledgements 368 Thanks (in alphabetical order by first name) to Bernie Volz, Brian 369 Haberman, Dmitry Anipko, Eric Levy-Abegnoli, Eric Vyncke, Erik 370 Nordmark, Fred Templin, Hilarie Orman, Jouni Korhonen, Michael 371 Sinatra, Ole Troan, Pascal Thubert, Ray Hunter, Suresh Krishnan, and 372 Tassos Chatzithomaoglou for their guidance and review of the 373 document. Thanks to Thomas Narten for encouraging this work. Thanks 374 to Steinar Haug and Scott Beuker for describing the use cases. 376 9. Normative References 378 [RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, 379 RFC 1661, July 1994. 381 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 382 Requirement Levels", BCP 14, RFC 2119, March 1997. 384 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. 386 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 387 Neighbor Discovery (SEND)", RFC 3971, March 2005. 389 [RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness 390 Requirements for Security", BCP 106, RFC 4086, June 2005. 392 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 393 for IPv6", RFC 4429, April 2006. 395 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 396 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 397 September 2007. 399 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 400 Address Autoconfiguration", RFC 4862, September 2007. 402 [RFC6620] Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS 403 SAVI: First-Come, First-Served Source Address Validation 404 Improvement for Locally Assigned IPv6 Addresses", RFC 405 6620, May 2012. 407 Authors' Addresses 409 Rajiv Asati 410 Cisco Systems, Inc. 411 7025 Kit Creek road 412 Research Triangle Park, NC 27709-4987 413 USA 415 Email: rajiva@cisco.com 416 URI: http://www.cisco.com/ 418 Hemant Singh 419 Cisco Systems, Inc. 420 1414 Massachusetts Ave. 421 Boxborough, MA 01719 422 USA 424 Phone: +1 978 936 1622 425 Email: shemant@cisco.com 426 URI: http://www.cisco.com/ 427 Wes Beebee 428 Cisco Systems, Inc. 429 1414 Massachusetts Ave. 430 Boxborough, MA 01719 431 USA 433 Phone: +1 978 936 2030 434 Email: wbeebee@cisco.com 435 URI: http://www.cisco.com/ 437 Carlos Pignataro 438 Cisco Systems, Inc. 439 7200-12 Kit Creek Road 440 Research Triangle Park, NC 27709 441 USA 443 Email: cpignata@cisco.com 444 URI: http://www.cisco.com/ 446 Eli Dart 447 Lawrence Berkeley National Laboratory 448 1 Cyclotron Road, Berkeley, CA 94720 449 USA 451 Email: dart@es.net 452 URI: http://www.es.net/ 454 Wesley George 455 Time Warner Cable 456 13820 Sunrise Valley Drive 457 Herndon, VA 20171 458 USA 460 Email: wesley.george@twcable.com