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(See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (July 21, 2014) is 3565 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) ** Obsolete normative reference: RFC 1583 (Obsoleted by RFC 2178) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 5 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, 3971 (if approved) W. Beebee 5 Intended status: Standards Track C. Pignataro 6 Expires: January 22, 2015 Cisco Systems, Inc. 7 E. Dart 8 Lawrence Berkeley National Laboratory 9 W. George 10 Time Warner Cable 11 July 21, 2014 13 Enhanced Duplicate Address Detection 14 draft-ietf-6man-enhanced-dad-06 16 Abstract 18 Appendix A of the IPv6 Duplicate Address Detection (DAD) document in 19 RFC 4862 discusses Loopback Suppression and DAD. However, RFC 4862 20 does not settle on one specific automated means to detect loopback of 21 Neighbor Discovery (ND of RFC 4861) messages used by DAD. Several 22 service provider communities have expressed a need for automated 23 detection of looped backed ND messages used by DAD. This document 24 includes mitigation techniques and then outlines the Enhanced DAD 25 algorithm to automate detection of looped back IPv6 ND messages used 26 by DAD. For network loopback tests, the Enhanced DAD algorithm 27 allows IPv6 to self-heal after a loopback is placed and removed. 28 Further, for certain access networks the document automates resolving 29 a specific duplicate address conflict. 31 Status of This Memo 33 This Internet-Draft is submitted in full conformance with the 34 provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF). Note that other groups may also distribute 38 working documents as Internet-Drafts. The list of current Internet- 39 Drafts is at http://datatracker.ietf.org/drafts/current/. 41 Internet-Drafts are draft documents valid for a maximum of six months 42 and may be updated, replaced, or obsoleted by other documents at any 43 time. It is inappropriate to use Internet-Drafts as reference 44 material or to cite them other than as "work in progress." 46 This Internet-Draft will expire on January 22, 2015. 48 Copyright Notice 50 Copyright (c) 2014 IETF Trust and the persons identified as the 51 document authors. All rights reserved. 53 This document is subject to BCP 78 and the IETF Trust's Legal 54 Provisions Relating to IETF Documents 55 (http://trustee.ietf.org/license-info) in effect on the date of 56 publication of this document. Please review these documents 57 carefully, as they describe your rights and restrictions with respect 58 to this document. Code Components extracted from this document must 59 include Simplified BSD License text as described in Section 4.e of 60 the Trust Legal Provisions and are provided without warranty as 61 described in the Simplified BSD License. 63 Table of Contents 65 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 66 1.1. Two Deployment Problems . . . . . . . . . . . . . . . . . 3 67 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 68 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 69 3. Operational Mitigation Options . . . . . . . . . . . . . . . 5 70 3.1. Disable DAD on Interface . . . . . . . . . . . . . . . . 5 71 3.2. Dynamic Disable/Enable of DAD Using Layer-2 Protocol . . 5 72 3.3. Operational Considerations . . . . . . . . . . . . . . . 6 73 4. The Enhanced DAD Algorithm . . . . . . . . . . . . . . . . . 6 74 4.1. General Rules . . . . . . . . . . . . . . . . . . . . . . 7 75 4.2. Processing Rules for Senders . . . . . . . . . . . . . . 7 76 4.3. Processing Rules for Receivers . . . . . . . . . . . . . 7 77 4.4. Impact on SEND . . . . . . . . . . . . . . . . . . . . . 8 78 4.5. Changes to RFC 4862 . . . . . . . . . . . . . . . . . . . 8 79 4.6. Changes to RFC 4861 . . . . . . . . . . . . . . . . . . . 9 80 4.7. Changes to RFC 3971 . . . . . . . . . . . . . . . . . . . 9 81 5. Actions to Perform on Detecting a Genuine Duplicate . . . . . 9 82 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 83 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 84 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 85 9. Normative References . . . . . . . . . . . . . . . . . . . . 10 86 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 88 1. Introduction 90 Appendix A of [RFC4862] discusses Loopback Suppression and Duplicate 91 Address Detection (DAD). However, [RFC4862] does not settle on one 92 specific automated means to detect loopback of ND messages used by 93 DAD. One specific DAD message is a Neighbor Solicitation (NS), 94 specified in [RFC4861]. The NS is issued by the network interface of 95 an IPv6 node for DAD. Another message involved in DAD is a Neighbor 96 Advertisement (NA). The Enhanced DAD algorithm proposed in this 97 document focuses on detecting an NS looped back to the transmitting 98 interface during the DAD operation. Detecting a looped back NA is of 99 no use because no problems with DAD will occur if a node receives a 100 looped back NA. Detection of any other looped back ND messages 101 outside of the DAD operation is not critical and thus this document 102 does not cover such detection. The document also includes a 103 Mitigation section that discusses means already available to mitigate 104 the loopback problem. 106 1.1. Two Deployment Problems 108 In each problem articulated below, the IPv6 link-local address DAD 109 operation fails due to a looped back DAD probe. However, the looped 110 back DAD probe exists for any IPv6 address type including global 111 addresses. 113 Recently, service providers have reported a problem with DAD that is 114 caused by looped back NS messages. The following is a description of 115 the circumstances under which the problem arises. Loopback testing 116 for troubleshooting purposes is underway on a circuit connected to an 117 interface on a router. The interface on the router is enabled for 118 IPv6. The interface issues a NS for the IPv6 link-local address DAD. 119 The NS is reflected back to the router interface due to the loopback 120 condition of the circuit, and the router interface enters a DAD- 121 failed state. After the circuit troubleshooting has concluded and 122 the loopback condition is removed, IPv4 will return to operation 123 without further manual intervention. However, IPv6 will remain in 124 DAD-failed state until manual intervention on the router restores 125 IPv6 to operation. 127 There are other conditions which will also trigger similar problems 128 with DAD Loopback. While the following example is not a common 129 configuration, it has occurred in a large service provider network. 130 It is necessary to address it in the proposed solution because the 131 trigger scenario has the potential to cause significant IPv6 service 132 outages when it does occur. Two broadband modems in the same home 133 are served by the same service provider and both modems are served by 134 one access concentrator and one layer-3 interface on the access 135 concentrator. The two modems have the Ethernet ports of each modem 136 connected to a network hub. The access concentrator serving the 137 modems is the first-hop IPv6 router for the modems. The network 138 interface of the access concentrator serving the two broadband modems 139 is enabled for IPv6 and the interface issues a NS(DAD) message for 140 the IPv6 link-local address. The NS message reaches one modem first 141 and this modem sends the message to the network hub which sends the 142 message to the second modem which forwards the message back to the 143 access concentrator. The looped back NS message causes the network 144 interface on the access concentrator to be in a DAD-failed state. 145 Such a network interface typically serves up to hundred thousands 146 broadband modems causing all the modems (and hosts behind the modems) 147 to fail to get IPv6 online on the access network. Additionally, it 148 may be tedious for the access concentrator to find out which of the 149 hundred thousand or more homes looped back the DAD message. Clearly 150 there is a need for automated detection of looped back NS messages 151 during DAD operations by a node. 153 2. Terminology 155 o DAD-failed state - Duplication Address Detection failure as 156 specified in [RFC4862]. Note even Optimistic DAD as specified in 157 [RFC4429] can fail due to a looped back DAD probe. This document 158 covers looped back detection for Optimistic DAD as well. 160 o Looped back message - also referred to as a reflected message. 161 The message sent by the sender is received by the sender due to 162 the network or a Upper Layer Protocol on the sender looping the 163 message back. 165 o Loopback - A function in which the router's layer-3 interface (or 166 the circuit to which the router's interface is connected) is 167 looped back or connected to itself. Loopback causes packets sent 168 by the interface to be received by the interface, and results in 169 interface unavailability for regular data traffic forwarding. See 170 more details in section 9.1 of [RFC1583]. The Loopback function 171 is commonly used in an interface context to gain information on 172 the quality of the interface, by employing mechanisms such as 173 ICMPv6 pings, bit-error tests, etc. In a circuit context, it is 174 used in wide area environments including optical dense wave 175 division multiplexing (DWDM) and SONET/SDH for fault isolation 176 (e.g. by placing a loopback at different geographic locations 177 along the path of a wide area circuit to help locate a circuit 178 fault). The Loopback function may be employed locally or 179 remotely. 181 o NS(DAD) - shorthand notation to denote an Neighbor Solicitation 182 (NS) (as specified in [RFC4861]) with unspecified IPv6 source- 183 address issued during DAD. 185 2.1. Requirements Language 187 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 188 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 189 document are to be interpreted as described in [RFC2119]. 191 3. Operational Mitigation Options 193 Two mitigation options are described below. The mechanisms do not 194 require any change to existing implementations. 196 3.1. Disable DAD on Interface 198 One can disable DAD on an interface and then there is no NS(DAD) 199 issued to be looped back. DAD is disabled by setting the interface's 200 DupAddrDetectTransmits variable to zero. While this mitigation may 201 be the simplest the mitigation has three drawbacks. 203 It would likely require careful analysis of configuration on such 204 point-to-point interfaces, a one-time manual configuration on each of 205 such interfaces, and more importantly, genuine duplicates in the link 206 will not be detected. 208 A Service Provider router such as an access concentrator or network 209 core router SHOULD support this mitigation strategy. 211 3.2. Dynamic Disable/Enable of DAD Using Layer-2 Protocol 213 It is possible that one or more layer-2 protocols include provisions 214 to detect the existence of a loopback on an interface circuit, 215 usually by comparing protocol data sent and received. For example, 216 PPP uses magic number (section 6.4 of [RFC1661]) to detect a loopback 217 on an interface. 219 When a layer-2 protocol detects that a loopback is present on an 220 interface circuit, the device MUST temporarily disable DAD on the 221 interface, and when the protocol detects that a loopback is no longer 222 present (or the interface state has changed), the device MUST 223 (re-)enable DAD on that interface. 225 This solution requires no protocol changes. This solution SHOULD be 226 enabled by default, and MUST be a configurable option if the layer-2 227 technology provides means for detecting loopback messages on an 228 interface circuit. 230 This mitigation has several benefits. They are 232 1. It leverages layer-2 protocol's built-in loopback detection 233 capability, if available. 235 2. It scales better since it relies on an event-driven model which 236 requires no additional state or timer. This may be a significant 237 scaling consideration on devices with hundreds or thousands of 238 interfaces that may be in loopback for long periods of time (such 239 as while awaiting turn-up or during long-duration intrusive bit 240 error rate tests). 242 3.3. Operational Considerations 244 The mitigation options discussed in the document do not require the 245 devices on both ends of the circuit to support the mitigation 246 functionality simultaneously, and do not propose any capability 247 negotiation. The mitigation options discussed in this document are 248 effective for unidirectional circuit or interface loopback (i.e. the 249 the loopback is placed in one direction on the circuit, rendering the 250 other direction non-operational). 252 The mitigation options may not be effective for the bidirectional 253 loopback (i.e. the loopback is placed in both directions of the 254 circuit interface, so as to identify the faulty segment) if only one 255 device followed a mitigation option specified in this document, since 256 the other device would follow current behavior and disable IPv6 on 257 that interface due to DAD until manual intervention restores it. 259 This is nothing different from what happens today (without the 260 solutions proposed by this document) in case of unidirectional 261 loopback. Hence, it is expected that an operator would resort to 262 manual intervention for the devices not compliant with this document, 263 as usual. 265 4. The Enhanced DAD Algorithm 267 The Enhanced DAD algorithm covers detection of a looped back NS(DAD) 268 message. The document proposes use of the Nonce Option specified in 269 the SEND document of [RFC3971]. The nonce is a random number as 270 specified in [RFC3971]. If SEND is enabled on the router and the 271 router also supports the Enhanced DAD algorithm (specified in this 272 document), there is integration with the Enhanced DAD algorithm and 273 SEND. See more details in the Impact on SEND section in section 4.4. 274 Since a nonce is used only once, DAD for each IPv6 address of an 275 interface uses a different nonce. Additional details of the 276 algorithm are included in section 4.2. 278 Six bytes of random nonce is sufficiently large for collisions. 279 However if there is a collision because two nodes that are using the 280 same Target Address in their NS(DAD) generated the same random nonce, 281 then the algorithm will incorrectly detect a looped back NS(DAD) when 282 a genuine address collision has occurred. Since each looped back 283 NS(DAD) event is logged to system management, the administrator of 284 the network will have access to the information necessary to 285 intervene manually. Also, because the nodes will have detected what 286 appear to be looped back NS(DAD) messages, they will continue to 287 probe and it is unlikely that they will choose the same nonce the 288 second time (assuming quality random number generators). 290 The algorithm is capable of detecting any ND solicitation (NS and 291 Router Solicitation) or advertisement (NA and Router Advertisement) 292 that is looped back. However, saving a nonce and nonce related data 293 for all ND messages has impact on memory of the node and also adds 294 the algorithm state to a substantially larger number of ND messages. 295 Therefore this document does not recommend using the algorithm 296 outside of the DAD operation by an interface on a node. 298 4.1. General Rules 300 If an IPv6 node implements the Enhanced DAD algorithm, the node MUST 301 implement detection of looped back NS(DAD) messages during DAD for an 302 interface address. 304 4.2. Processing Rules for Senders 306 If a node has been configured to use the Enhanced DAD algorithm, when 307 sending a NS(DAD) for a tentative or optimistic interface address the 308 sender MUST generate a random nonce associated with the interface 309 address, MUST save the nonce, and MUST include the nonce in the Nonce 310 Option included in the NS(DAD). If the interface does not receive 311 any DAD failure indications within RetransTimer milliseconds (see 312 [RFC4861]) after having sent DupAddrDetectTransmits Neighbor 313 Solicitations, the interface moves the Target Address to assigned 314 state. 316 If any probe is looped back within RetransTimer milliseconds after 317 having sent DupAddrDetectTransmits NS(DAD) messages, the interface 318 continues with another MAX_MULTICAST_SOLICIT number of NS(DAD) 319 messages transmitted RetransTimer millseconds apart. If no probe is 320 looped back within RetransTimer milliseconds after 321 MAX_MULTICAST_SOLICIT NS(DAD) messages are sent, the probing stops. 322 The probing MAY be stopped via manual intervention. When probing is 323 stopped, the interface moves the Target Address to assigned state. 325 4.3. Processing Rules for Receivers 327 If the node has been configured to use the Enhanced DAD algorithm and 328 an interface on the node receives any NS(DAD) message where the 329 Target Address matches the interface address (in tentative or 330 optimistic state), the receiver compares the nonce included in the 331 message, if any, with any saved nonce on the receiving interface. If 332 a match is found, the node SHOULD log a system management message, 333 SHOULD update any statistics counter, MUST drop the received message. 334 If the received NS(DAD) message includes a nonce and no match is 335 found with any saved nonce, the node SHOULD log a system management 336 message for DAD-failed and SHOULD update any statistics counter. If 337 the interface does not receive any DAD failure indications within 338 RetransTimer milliseconds after having sent DupAddrDetectTransmits 339 Neighbor Solicitations, the interface moves the Target Address to 340 assigned state. 342 4.4. Impact on SEND 344 The SEND document uses the Nonce Option in the context of matching an 345 NA with an NS. However, no text in SEND has an explicit mention of 346 detecting looped back ND messages. If this document updates 347 [RFC4862], SEND should be updated to integrate with the Enhanced DAD 348 algorithm. A minor update to SEND would be to explicitly mention 349 that the nonce in SEND is also used by SEND to detect looped back NS 350 messages during DAD operations by the node. In a mixed SEND 351 environment with SEND and unsecured nodes, the lengths of the nonce 352 used by SEND and unsecured nodes MUST be identical. 354 4.5. Changes to RFC 4862 356 The following text is added to the end of the Introduction section of 357 [RFC4862]. 359 A network interface of an IPv6 node SHOULD implement the Enhanced DAD 360 algorithm. For example, if the interface on an IPv6 node is 361 connected to a circuit that supports loopback testing, then the node 362 should implement the Enhanced DAD algorithm that allows the IPv6 363 interface to self-heal after loopback testing is ended on the 364 circuit. Another example is when the IPv6 interface resides on an 365 access concentrator running DAD Proxy. The interface supports up to 366 hundred thousands IPv6 clients (broadband modems) connected to the 367 interface. If the interface performs DAD for its IPv6 link-local 368 address and if the DAD probe is reflected back to the interface, the 369 interface is stuck in DAD failed state and IPv6 services to the 370 hundred thousands clients is denied. Disabling DAD for such an IPv6 371 interface on an access concentrator is less desirable than 372 implementing the algorithm because the network also needs to detect 373 genuine duplicates in the interface downstream network. The Enhanced 374 DAD algorithm also facilitates detecting a genuine duplicate for the 375 interface on the access concentrator. See the Actions to Perform on 376 Detecting a Genuine Duplicate section of the Enhanced DAD document. 378 The following text is added to the end of Appendix A of [RFC4862]. 380 The Enhanced DAD algorithm from draft-ietf-6man-enhanced-dad is 381 designed to detect looped back DAD probes. A network interface of an 382 IPv6 node SHOULD implement the Enhanced DAD algorithm. 384 4.6. Changes to RFC 4861 386 The following text is appended to the RetransTimer variable 387 description in section 6.3.2 of [RFC4861]. 389 The RetransTimer may be overridden by a link-specific document if a 390 node supports the Enhanced DAD algorithm. 392 The following text is appended to the Source Address definition in 393 section 4.3 of [RFC4861]. 395 If a node has been configured to use the Enhanced DAD algorithm, an 396 NS with an unspecified source address adds the Nonce option to the 397 message and implements the state machine of the Enhanced DAD 398 algorithm. 400 4.7. Changes to RFC 3971 402 The following text is changed in section 5.3.2 of [RFC3971]. 404 The purpose of the Nonce option is to make sure that an advertisement 405 is a fresh response to a solicitation sent earlier by the node. 407 New text is included below. 409 The purpose of the Nonce option is to make sure that an advertisement 410 is a fresh response to a solicitation sent earlier by the node. The 411 nonce is also used to detect looped back NS messages when the network 412 interface performs DAD [RFC4862]. Detecting looped back DAD messages 413 is covered by the Enhanced DAD algorithm as specified in draft-ietf- 414 6man-enhanced-dad. In a mixed SEND environment with SEND and 415 unsecured nodes, the lengths of the nonce used by SEND and unsecured 416 nodes MUST be identical. 418 5. Actions to Perform on Detecting a Genuine Duplicate 420 As described in paragraphs above the nonce can also serve to detect 421 genuine duplicates even when the network has potential for looping 422 back ND messages. When a genuine duplicate is detected, the node 423 follows the manual intervention specified in section 5.4.5 of 424 [RFC4862]. However, in certain networks such as an access network if 425 the genuine duplicate matches the tentative or optimistic IPv6 426 address of a network interface of the access concentrator, automated 427 actions are proposed. 429 One access network is a cable broadband deployment where the access 430 concentrator is the first-hop IPv6 router to several thousand 431 broadband modems. The router also supports proxying of DAD messages. 433 The network interface on the access concentrator initiates DAD for an 434 IPv6 address and detects a genuine duplicate due to receiving an 435 NS(DAD) or an NA message. On detecting such a duplicate the access 436 concentrator logs a system management message, drops the received ND 437 message, and blocks the modem on whose layer-2 service identifier the 438 NS(DAD) or NA message was received on. 440 The network described above follows a trust model where a trusted 441 router serves un-trusted IPv6 host nodes. Operators of such networks 442 have a desire to take automated action if a network interface of the 443 trusted router has a tentative or optimistic address duplicate with a 444 host served by trusted router interface. Any other network that 445 follows the same trust model MAY use the automated actions proposed 446 in this section. 448 6. Security Considerations 450 The nonce can be exploited by a rogue deliberately changing the nonce 451 to fail the looped back detection specified by the Enhanced DAD 452 algorithm. SEND is recommended to circumvent this exploit. 453 Additionally, the nonce does not protect against the DoS caused by a 454 rogue node replying by fake NA to all DAD probes. SEND is 455 recommended to circumvent this exploit. For any mitigation suggested 456 in the document such as disabling DAD has an obvious security issue 457 before a remote node on the link can issue reflected NS(DAD) 458 messages. Again, SEND is recommended for this exploit. 460 7. IANA Considerations 462 None. 464 8. Acknowledgements 466 Thanks (in alphabetical order by first name) to Dmitry Anipko, Eric 467 Levy-Abegnoli, Eric Vyncke, Erik Nordmark, Fred Templin, Jouni 468 Korhonen, Michael Sinatra, Ole Troan, Ray Hunter, Suresh Krishnan, 469 and Tassos Chatzithomaoglou for their guidance and review of the 470 document. Thanks to Thomas Narten for encouraging this work. Thanks 471 to Steinar Haug and Scott Beuker for describing the use cases. 473 9. Normative References 475 [RFC1583] Moy, J., "OSPF Version 2", RFC 1583, March 1994. 477 [RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, 478 RFC 1661, July 1994. 480 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 481 Requirement Levels", BCP 14, RFC 2119, March 1997. 483 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 484 Neighbor Discovery (SEND)", RFC 3971, March 2005. 486 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 487 for IPv6", RFC 4429, April 2006. 489 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 490 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 491 September 2007. 493 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 494 Address Autoconfiguration", RFC 4862, September 2007. 496 Authors' Addresses 498 Rajiv Asati 499 Cisco Systems, Inc. 500 7025 Kit Creek road 501 Research Triangle Park, NC 27709-4987 502 USA 504 Email: rajiva@cisco.com 505 URI: http://www.cisco.com/ 507 Hemant Singh 508 Cisco Systems, Inc. 509 1414 Massachusetts Ave. 510 Boxborough, MA 01719 511 USA 513 Phone: +1 978 936 1622 514 Email: shemant@cisco.com 515 URI: http://www.cisco.com/ 517 Wes Beebee 518 Cisco Systems, Inc. 519 1414 Massachusetts Ave. 520 Boxborough, MA 01719 521 USA 523 Phone: +1 978 936 2030 524 Email: wbeebee@cisco.com 525 URI: http://www.cisco.com/ 526 Carlos Pignataro 527 Cisco Systems, Inc. 528 7200-12 Kit Creek Road 529 Research Triangle Park, NC 27709 530 USA 532 Email: cpignata@cisco.com 533 URI: http://www.cisco.com/ 535 Eli Dart 536 Lawrence Berkeley National Laboratory 537 1 Cyclotron Road, Berkeley, CA 94720 538 USA 540 Email: dart@es.net 541 URI: http://www.es.net/ 543 Wes George 544 Time Warner Cable 545 13820 Sunrise Valley Drive 546 Herndon, VA 20171 547 USA 549 Email: wesley.george@twcable.com