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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) == Missing Reference: 'IDr' is mentioned on line 256, but not defined == Missing Reference: 'KEi' is mentioned on line 315, but not defined == Missing Reference: 'KEr' is mentioned on line 317, but not defined == Missing Reference: 'CERTREQ' is mentioned on line 588, but not defined ** Obsolete normative reference: RFC 4306 (Obsoleted by RFC 5996) ** Obsolete normative reference: RFC 4718 (Obsoleted by RFC 5996) Summary: 3 errors (**), 0 flaws (~~), 5 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Y. Nir 3 Internet-Draft Check Point 4 Intended status: Standards Track F. Detienne 5 Expires: July 23, 2010 P. Sethi 6 Cisco 7 January 19, 2010 9 A Quick Crash Detection Method for IKE 10 draft-nir-ike-qcd-06 12 Status of this Memo 14 This Internet-Draft is submitted to IETF in full conformance with the 15 provisions of BCP 78 and BCP 79. 17 Internet-Drafts are working documents of the Internet Engineering 18 Task Force (IETF), its areas, and its working groups. Note that 19 other groups may also distribute working documents as Internet- 20 Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference 25 material or to cite them other than as "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/ietf/1id-abstracts.txt. 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html. 33 This Internet-Draft will expire on July 23, 2010. 35 Copyright Notice 37 Copyright (c) 2010 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents in effect on the date of 42 publication of this document (http://trustee.ietf.org/license-info). 43 Please review these documents carefully, as they describe your rights 44 and restrictions with respect to this document. 46 Abstract 48 This document describes an extension to the IKEv2 protocol that 49 allows for faster detection of SA desynchronization using a saved 50 token. 52 When an IPsec tunnel between two IKEv2 peers is disconnected due to a 53 restart of one peer, it can take as much as several minutes for the 54 other peer to discover that the reboot has occurred, thus delaying 55 recovery. In this text we propose an extension to the protocol, that 56 allows for recovery immediately following the restart. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 61 1.1. Conventions Used in This Document . . . . . . . . . . . . 4 62 2. RFC 4306 Crash Recovery . . . . . . . . . . . . . . . . . . . 5 63 3. Protocol Outline . . . . . . . . . . . . . . . . . . . . . . . 5 64 4. Formats and Exchanges . . . . . . . . . . . . . . . . . . . . 6 65 4.1. Notification Format . . . . . . . . . . . . . . . . . . . 6 66 4.2. Passing a Token in the AUTH Exchange . . . . . . . . . . . 7 67 4.3. Replacing Tokens After Rekey or Resumption . . . . . . . . 8 68 4.4. Replacing the Token for an Existing SA . . . . . . . . . . 9 69 4.5. Presenting the Token in an INFORMATIONAL Exchange . . . . 9 70 5. Token Generation and Verification . . . . . . . . . . . . . . 10 71 5.1. A Stateless Method of Token Generation . . . . . . . . . . 10 72 5.2. A Stateless Method with IP addresses . . . . . . . . . . . 11 73 5.3. Token Lifetime . . . . . . . . . . . . . . . . . . . . . . 11 74 6. Backup Gateways . . . . . . . . . . . . . . . . . . . . . . . 11 75 7. Alternative Solutions . . . . . . . . . . . . . . . . . . . . 12 76 7.1. Initiating a new IKE SA . . . . . . . . . . . . . . . . . 12 77 7.2. Birth Certificates . . . . . . . . . . . . . . . . . . . . 12 78 7.3. Reducing Liveness Check Length . . . . . . . . . . . . . . 13 79 8. Interaction with Session Resumption . . . . . . . . . . . . . 13 80 9. Operational Considerations . . . . . . . . . . . . . . . . . . 14 81 9.1. Who should implement this specification . . . . . . . . . 14 82 9.2. Response to unknown child SPI . . . . . . . . . . . . . . 15 83 9.3. Using Tokens that Depend on IP Addresses . . . . . . . . . 16 84 10. Security Considerations . . . . . . . . . . . . . . . . . . . 16 85 10.1. QCD Token Generation and Handling . . . . . . . . . . . . 16 86 10.2. QCD Token Transmission . . . . . . . . . . . . . . . . . . 17 87 10.3. QCD Token Enumeration . . . . . . . . . . . . . . . . . . 17 88 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 89 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18 90 13. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 18 91 13.1. Changes from draft-nir-ike-qcd-03 and -04 . . . . . . . . 18 92 13.2. Changes from draft-nir-ike-qcd-02 . . . . . . . . . . . . 18 93 13.3. Changes from draft-nir-ike-qcd-01 . . . . . . . . . . . . 19 94 13.4. Changes from draft-nir-ike-qcd-00 . . . . . . . . . . . . 19 95 13.5. Changes from draft-nir-qcr-00 . . . . . . . . . . . . . . 19 96 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19 97 14.1. Normative References . . . . . . . . . . . . . . . . . . . 19 98 14.2. Informative References . . . . . . . . . . . . . . . . . . 19 99 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 101 1. Introduction 103 IKEv2, as described in [RFC4306] has a method for recovering from a 104 reboot of one peer. As long as traffic flows in both directions, the 105 rebooted peer should re-establish the tunnels immediately. However, 106 in many cases the rebooted peer is a VPN gateway that protects only 107 servers, or else the non-rebooted peer has a dynamic IP address. In 108 such cases, the rebooted peer will not be able to re-establish the 109 tunnels. Section 2 describes how recovery works under RFC 4306, and 110 explains why it may take several minutes. 112 The method proposed here, is to send an octet string, called a "QCD 113 token" in the IKE_AUTH exchange that establishes the tunnel. That 114 token can be stored on the peer as part of the IKE SA. After a 115 reboot, the rebooted implementation can re-generate the token, and 116 send it to the peer, so as to delete the IKE SA. Deleting the IKE SA 117 results is a quick establishment of new IPsec tunnels. This is 118 described in Section 3. 120 1.1. Conventions Used in This Document 122 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 123 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 124 document are to be interpreted as described in [RFC2119]. 126 The term "token" refers to an octet string that an implementation can 127 generate using only the properties of a protected IKE message (such 128 as IKE SPIs) as input. A conforming implementation MUST be able to 129 generate the same token from the same input even after rebooting. 131 The term "token maker" refers to an implementation that generates a 132 token and sends it to the peer as specified in this document. 134 The term "token taker" refers to an implementation that stores such a 135 token or a digest thereof, in order to verify that a new token it 136 receives is identical to the old token it has stored. 138 The term "non-volatile storage" in this document refers to a data 139 storage module, that persists across restarts of the token maker. 140 Examples of such a storage module include an internal disk, an 141 internal flash memory module, an external disk and an external 142 database. A small non-volatile storage module is required for a 143 token maker, but a larger one can be used to enhance performance, as 144 described in Section 9.2. 146 2. RFC 4306 Crash Recovery 148 When one peer loses state or reboots, the other peer does not get any 149 notification, so unidirectional IPsec traffic can still flow. The 150 rebooted peer will not be able to decrypt it, however, and the only 151 remedy is to send an unprotected INVALID_SPI notification as 152 described in section 3.10.1 of [RFC4306]. That section also 153 describes the processing of such a notification: 155 "If this Informational Message is sent outside the 156 context of an IKE_SA, it should be used by the recipient 157 only as a "hint" that something might be wrong (because it 158 could easily be forged)." 160 Since the INVALID_SPI can only be used as a hint, the non-rebooted 161 peer has to determine whether the IPsec SA, and indeed the parent IKE 162 SA are still valid. The method of doing this is described in section 163 2.4 of [RFC4306]. This method, called "liveness check" involves 164 sending a protected empty INFORMATIONAL message, and awaiting a 165 response. This procedure is sometimes referred to as "Dead Peer 166 Detection" or DPD. 168 Section 2.4 does not mandate how many times the liveness check 169 message should be retransmitted, or for how long, but does recommend 170 the following: 172 "It is 173 suggested that messages be retransmitted at least a dozen times over 174 a period of at least several minutes before giving up on an SA..." 176 Those "at least several minutes" are a time during which both peers 177 are active, but IPsec cannot be used. 179 3. Protocol Outline 181 Supporting implementations will send a notification, called a "QCD 182 token", as described in Section 4.1 in the last IKE_AUTH exchange 183 messages. These are the final IKE_AUTH request and final IKE_AUTH 184 response that contain the AUTH payloads. The generation of these 185 tokens is a local matter for implementations, but considerations are 186 described in Section 5. Implementations that send such a token will 187 be called "token makers". 189 A supporting implementation receiving such a token MUST store it (or 190 a digest thereof) as part of the IKE SA. Implementations that 191 support this part of the protocol will be called "token takers". 192 Section 9.1 has considerations for which implementations need to be 193 token takers, and which should be token makers. Implementation that 194 are not token takers will silently ignore QCD tokens. 196 When a token maker receives a protected IKE request message with 197 unknown IKE SPIs, it MUST generate a new token that is identical to 198 the previous token, and send it to the requesting peer in an 199 unprotected IKE message as described in Section 4.5. 201 When a token taker receives the QCD token in an unprotected 202 notification, it MUST verify that the TOKEN_SECRET_DATA matches the 203 token stored in the matching IKE SA. If the verification fails, or 204 if the IKE SPIs in the message do not match any existing IKE SA, it 205 SHOULD log the event. If it succeeds, it MUST silently delete the 206 IKE SA associated with the IKE_SPI fields, and all dependant child 207 SAs. This event MAY also be logged. The token taker MUST accept 208 such tokens from any IP address and port combination, so as to allow 209 different kinds of high-availability configurations of the token 210 maker. 212 A supporting token taker MAY immediately create new SAs using an 213 Initial exchange, or it may wait for subsequent traffic to trigger 214 the creation of new SAs. 216 There is ongoing work on IKEv2 Session Resumption ([resumption]). 217 See Section 8 for a short discussion about this extensions's 218 interaction with session resumption. 220 4. Formats and Exchanges 222 4.1. Notification Format 224 The notification payload called "QCD token" is formatted as follows: 226 1 2 3 227 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 1 228 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 229 ! Next Payload !C! RESERVED ! Payload Length ! 230 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 231 ! Protocol ID ! SPI Size ! QCD Token Notify Message Type ! 232 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 233 ! ! 234 ~ TOKEN_SECRET_DATA ~ 235 ! ! 236 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 238 o Protocol ID (1 octet) MUST be 1, as this message is related to an 239 IKE SA. 240 o SPI Size (1 octet) MUST be zero, in conformance with section 3.10 241 of [RFC4306]. 242 o QCD Token Notify Message Type (2 octets) - MUST be xxxxx, the 243 value assigned for QCD token notifications. TBA by IANA. 244 o TOKEN_SECRET_DATA (16-128 octets) contains a generated token as 245 described in Section 5. 247 4.2. Passing a Token in the AUTH Exchange 249 For brevity, only the EAP version of an AUTH exchange will be 250 presented here. The non-EAP version is very similar. The figures 251 below are based on appendix A.3 of [RFC4718]. 253 first request --> IDi, 254 [N(INITIAL_CONTACT)], 255 [[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+], 256 [IDr], 257 [CP(CFG_REQUEST)], 258 [N(IPCOMP_SUPPORTED)+], 259 [N(USE_TRANSPORT_MODE)], 260 [N(ESP_TFC_PADDING_NOT_SUPPORTED)], 261 [N(NON_FIRST_FRAGMENTS_ALSO)], 262 SA, TSi, TSr, 263 [V+] 265 first response <-- IDr, [CERT+], AUTH, 266 EAP, 267 [V+] 269 / --> EAP 270 repeat 1..N times | 271 \ <-- EAP 273 last request --> AUTH 274 [N(QCD_TOKEN)] 276 last response <-- AUTH, 277 [N(QCD_TOKEN)] 278 [CP(CFG_REPLY)], 279 [N(IPCOMP_SUPPORTED)], 280 [N(USE_TRANSPORT_MODE)], 281 [N(ESP_TFC_PADDING_NOT_SUPPORTED)], 282 [N(NON_FIRST_FRAGMENTS_ALSO)], 283 SA, TSi, TSr, 284 [N(ADDITIONAL_TS_POSSIBLE)], 285 [V+] 287 Note that the QCD_TOKEN notification is marked as optional because it 288 is not required by this specification that every implementation be 289 both token maker and token taker. If only one peer sends the QCD 290 token, then a reboot of the other peer will not be recoverable by 291 this method. This may be acceptable if traffic typically originates 292 from the other peer. 294 In any case, the lack of a QCD_TOKEN notification MUST NOT be taken 295 as an indication that the peer does not support this standard. 296 Conversely, if a peer does not understand this notification, it will 297 simply ignore it. Therefore a peer MAY send this notification 298 freely, even if it does not know whether the other side supports it. 300 The QCD_TOKEN notification is related to the IKE SA and MUST follow 301 the AUTH payload and precede the Configuration payload and all 302 payloads related to the child SA. 304 4.3. Replacing Tokens After Rekey or Resumption 306 After rekeying an IKE SA, the IKE SPIs are replaced, so the new SA 307 also needs to have a token. If only the responder in the rekey 308 exchange is the token maker, this can be done within the 309 CREATE_CHILD_SA exchange. If the initiator is a token maker, then we 310 need an extra informational exchange. 312 The following figure shows the CREATE_CHILD_SA exchange for rekeying 313 the IKE SA. Only the responder sends a QCD token. 315 request --> SA, Ni, [KEi] 317 response <-- SA, Nr, [KEr], N(QCD_TOKEN) 319 If the initiator is also a token maker, it SHOULD soon initiate an 320 INFORMATIONAL exchange as follows: 322 request --> N(QCD_TOKEN) 324 response <-- 326 For session resumption, as specified in [resumption], the situation 327 is similar. The responder, which is necessarily the peer that has 328 crashed, SHOULD send a new ticket within the protected payload of the 329 IKE_SESSION_RESUME exchange. If the Initiator is also a token maker, 330 it needs to send a QCD_TOKEN in a separate INFORMATIONAL exchange. 332 The INFORMATIONAL exchange described in this section can also be used 333 if QCD tokens need to be replaced due to a key rollover. However, 334 since token takers are required to verify at least 4 QCD tokens, this 335 is only necessary if secret QCD keys are rolled over more than four 336 times as often as IKE SAs are rekeyed. 338 4.4. Replacing the Token for an Existing SA 340 With some token generation methods, such as that described in 341 Section 5.2, a QCD token may sometimes become invalid, although the 342 IKE SA is still perfectly valid. 344 In such a case, the token maker MUST send the new token in a 345 protected message under that IKE SA. That exchange could be a simple 346 INFORMATIONAL, such as in the last figure in the previous section, or 347 else it can be part of a MOBIKE INFORMATIONAL exchange such as in the 348 following figure taken from section 2.2 of [RFC4555] and modified by 349 adding a QCD_TOKEN notification: 351 (IP_I2:4500 -> IP_R1:4500) 352 HDR, SK { N(UPDATE_SA_ADDRESSES), 353 N(NAT_DETECTION_SOURCE_IP), 354 N(NAT_DETECTION_DESTINATION_IP) } --> 356 <-- (IP_R1:4500 -> IP_I2:4500) 357 HDR, SK { N(NAT_DETECTION_SOURCE_IP), 358 N(NAT_DETECTION_DESTINATION_IP) } 360 <-- (IP_R1:4500 -> IP_I2:4500) 361 HDR, SK { N(COOKIE2), [N(QCD_TOKEN)] } 363 (IP_I2:4500 -> IP_R1:4500) 364 HDR, SK { N(COOKIE2), [N(QCD_TOKEN)] } --> 366 A token taker MUST accept such gratuitous QCD_TOKEN notifications as 367 long as they are carried in protected exchanges. A token maker 368 SHOULD NOT generate them unless it is no longer able to generate the 369 old QCD_TOKEN. 371 4.5. Presenting the Token in an INFORMATIONAL Exchange 373 This QCD_TOKEN notification is unprotected, and is sent as a response 374 to a protected IKE request, which uses an IKE SA that is unknown. 376 request --> N(INVALID_IKE_SPI), N(QCD_TOKEN)+ 378 If child SPIs are persistently mapped to IKE SPIs as described in 379 Section 9.2, a token taker may get the following unprotected message 380 in response to an ESP or AH packet. 382 request --> N(INVALID_SPI), N(QCD_TOKEN)+ 384 The QCD_TOKEN and INVALID_IKE_SPI notifications are sent together to 385 support both implementations that conform to this specification and 386 implementations that don't. Similar to the description in section 387 2.21 of [RFC4306], The IKE SPI and message ID fields in the packet 388 headers are taken from the protected IKE request. 390 To support a periodic rollover of the secret used for token 391 generation, the token taker MUST support at least four QCD_TOKEN 392 notifications in a single packet. The token is considered verified 393 if any of the QCD_TOKEN notifications matches. The token maker MAY 394 generate up to four QCD_TOKEN notifications, based on several 395 generations of keys. 397 If the QCD_TOKEN verifies OK, an empty response MUST be sent. If the 398 QCD_TOKEN cannot be validated, a response MUST NOT be sent. 399 Section 5 defines token verification. 401 5. Token Generation and Verification 403 No token generation method is mandated by this document. Two method 404 are documented in the following sub-sections, but they only serve as 405 examples. 407 The following lists the requirements from a token generation 408 mechanism: 409 o Tokens MUST be at least 16 octets long, and no more than 128 410 octets long, to facilitate storage and transmission. Tokens 411 SHOULD be indistinguishable from random data. 412 o It should not be possible for an external attacker to guess the 413 QCD token generated by an implementation. Cryptographic 414 mechanisms such as PRNG and hash functions are RECOMMENDED. 415 o The token maker, MUST be able to re-generate or retrieve the token 416 based on the IKE SPIs even after it reboots. 418 5.1. A Stateless Method of Token Generation 420 This describes a stateless method of generating a token: 421 o At installation or immediately after the first boot of the token 422 maker, 32 random octets are generated using a secure random number 423 generator or a PRNG. 424 o Those 32 bytes, called the "QCD_SECRET", are stored in non- 425 volatile storage on the machine, and kept indefinitely. 426 o If key rollover is required by policy, the implementation MAY 427 periodically generate a new QCD_SECRET and keep up to 3 previous 428 generations. When sending an unprotected QCD_TOKEN, as many as 4 429 notification payloads may be sent, each from a different 430 QCD_SECRET. 432 o The TOKEN_SECRET_DATA is calculated as follows: 434 TOKEN_SECRET_DATA = HASH(QCD_SECRET | SPI-I | SPI-R) 436 5.2. A Stateless Method with IP addresses 438 This method is similar to the one in the previous section, except 439 that the IP address of the token taker is also added to the block 440 being hashed. This has the disadvantage that the token needs to be 441 replaced (as described in Section 4.4) whenever the token taker 442 changes its address. 444 The reason to use this method is described in Section 9.3. When 445 using this method, the TOKEN_SECRET_DATA field is calculated as 446 follows: 448 TOKEN_SECRET_DATA = HASH(QCD_SECRET | SPI-I | SPI-R | IPaddr-T) 450 The IPaddr-T field specifies the IP address of the token taker. 451 Secret rollover considerations are similar to those in the previous 452 section. 454 5.3. Token Lifetime 456 The token is associated with a single IKE SA, and SHOULD be deleted 457 by the token taker when the SA is deleted or expires. More formally, 458 the token is associated with the pair (SPI-I, SPI-R). 460 6. Backup Gateways 462 Making crash detection and recovery quick is a worthy goal, but since 463 rebooting a gateway takes a non-zero amount of time, many 464 implementations choose to have a stand-by gateway ready to take over 465 as soon as the primary gateway fails for any reason. 467 If such a configuration is available, it is RECOMMENDED that the 468 stand-by gateway be able to generate the same token as the active 469 gateway. if the method described in Section 5.1 is used, this means 470 that the QCD_SECRET field is identical in both gateways. This has 471 the effect of having the crash recovery available immediately. 473 Note that this refers to "high availability" configurations, where 474 only one gateway is active at any given moment. This is different 475 from "load sharing" configurations where more than one gateway is 476 active at the same time. This is also different from high 477 availability configurations where the SAs are synchronized. For load 478 sharing configurations, please see Section 10.2 for security 479 considerations. 481 7. Alternative Solutions 483 7.1. Initiating a new IKE SA 485 Instead of sending a QCD token, we could have the rebooted 486 implementation start an Initial exchange with the peer, including the 487 INITIAL_CONTACT notification. This would have the same effect, 488 instructing the peer to erase the old IKE SA, as well as establishing 489 a new IKE SA with fewer rounds. 491 The disadvantage here, is that in IKEv2 an authentication exchange 492 MUST have a piggy-backed Child SA set up. Since our use case is such 493 that the rebooted implementation does not have traffic flowing to the 494 peer, there are no good selectors for such a Child SA. 496 Additionally, when authentication is asymmetric, such as when EAP is 497 used, it is not possible for the rebooted implementation to initiate 498 IKE. 500 7.2. Birth Certificates 502 Birth Certificates is a method of crash detection that has never been 503 formally defined. Bill Sommerfeld suggested this idea in a mail to 504 the IPsec mailing list on August 7, 2000, in a thread discussing 505 methods of crash detection: 507 If we have the system sign a "birth certificate" when it 508 reboots (including a reboot time or boot sequence number), 509 we could include that with a "bad spi" ICMP error and in 510 the negotiation of the IKE SA. 512 We believe that this method would have some problems. First, it 513 requires Alice to store the certificate, so as to be able to compare 514 the public keys. That requires more storage than does a QCD token. 515 Additionally, the public-key operations needed to verify the self- 516 signed certificates are more expensive for Alice. 518 We believe that a symmetric-key operation such as proposed here is 519 more light-weight and simple than that implied by the Birth 520 Certificate idea. 522 7.3. Reducing Liveness Check Length 524 Some have suggested that the RFC 4306 procedure described in 525 Section 2 can be tweaked by requiring fewer retransmissions over a 526 shorter period of time for cases of liveness check started because of 527 an INVALID_SPI or INVALID_IKE_SPI notification. 529 We believe that the default retransmission policy should represent a 530 good balance between the need for a timely discovery of a dead peer, 531 and a low probability of false detection. We expect the policy to be 532 set to take the shortest time such that this probability achieves a 533 certain target. Therefore, reducing elapsed time and retransmission 534 count will create an unacceptably high probability of false 535 detection, and this can be triggered by a single INVALID_IKE_SPI 536 notification. 538 Additionally, even if the retransmission policy is reduced to, say, 539 one minute, it is still a very noticeable delay from a human 540 perspective, from the time that the gateway has come up until the 541 tunnels are active, or from the time the backup gateway has taken 542 over until the tunnels are active. 544 8. Interaction with Session Resumption 546 Session Resumption, specified in [resumption] proposes to make 547 setting up a new IKE SA consume less computing resources. This is 548 particularly useful in the case of a remote access gateway that has 549 many tunnels. A failure of such a gateway would require all these 550 many remote access clients to establish an IKE SA either with the 551 rebooted gateway or with a backup gateway. This tunnel re- 552 establishment should occur within a short period of time, creating a 553 burden on the remote access gateway. Session Resumption addresses 554 this problem by having the clients store an encrypted derivative of 555 the IKE SA for quick re-establishment. 557 What Session Resumption does not help, is the problem of detecting 558 that the peer gateway has failed. A failed gateway may go undetected 559 for as long as the lifetime of a child SA, because IPsec does not 560 have packet acknowledgement, and applications cannot signal the IPsec 561 layer that the tunnel "does not work". Before establishing a new IKE 562 SA using Session Resumption, a client should ascertain that the 563 gateway has indeed failed. This could be done using either a 564 liveness check (as in RFC 4306) or using the QCD tokens described in 565 this document. 567 A remote access client conforming to both specifications will store 568 QCD tokens, as well as the Session Resumption ticket, if provided by 569 the gateway. A remote access gateway conforming to both 570 specifications will generate a QCD token for the client. When the 571 gateway reboots, the client will discover this in either of two ways: 572 1. The client does regular liveness checks, or else the time for 573 some other IKE exchange has come. Since the gateway is still 574 down, the IKE exchange times out after several minutes. In this 575 case QCD does not help. 576 2. Either the primary gateway or a backup gateway (see Section 6) is 577 ready and sends a QCD token to the client. In that case the 578 client will quickly re-establish the IPsec tunnel, either with 579 the rebooted primary gateway or the backup gateway as described 580 in this document. 582 The full combined protocol looks like this: 584 Initiator Responder 585 ----------- ----------- 586 HDR, SAi1, KEi, Ni --> 588 <-- HDR, SAr1, KEr, Nr, [CERTREQ] 590 HDR, SK {IDi, [CERT,] 591 [CERTREQ,] [IDr,] 592 AUTH, N(QCD_TOKEN) 593 SAi2, TSi, TSr, 594 N(TICKET_REQUEST)} --> 595 <-- HDR, SK {IDr, [CERT,] AUTH, 596 N(QCD_TOKEN), SAr2, TSi, TSr, 597 N(TICKET_LT_OPAQUE) } 599 ---- Reboot ----- 601 HDR, {} --> 602 <-- HDR, N(QCD_TOKEN) 604 HDR, [N(COOKIE),] 605 Ni, N(TICKET_OPAQUE) 606 [,N+] --> 607 <-- HDR, Nr [,N+] 609 9. Operational Considerations 611 9.1. Who should implement this specification 613 Throughout this document, we have referred to reboot time 614 alternatingly as the time that the implementation crashes and the 615 time when it is ready to process IPsec packets and IKE exchanges. 616 Depending on the hardware and software platforms and the cause of the 617 reboot, rebooting may take anywhere from a few seconds to several 618 minutes. If the implementation is down for a long time, the benefit 619 of this protocol extension is reduced. For this reason critical 620 systems should implement backup gateways as described in Section 6. 622 Implementing the "token maker" side of QCD makes sense for IKE 623 implementation where protected connections originate from the peer, 624 such as inter-domain VPNs and remote access gateways. Implementing 625 the "token taker" side of QCD makes sense for IKE implementations 626 where protected connections originate, such as inter-domain VPNs and 627 remote access clients. 629 To clarify the requirements: 630 o A remote-access client MUST be a token taker and MAY be a token 631 maker. 632 o A remote-access gateway MAY be a token taker and MUST be a token 633 maker. 634 o An inter-domain VPN gateway MUST be both token maker and token 635 taker. 637 In order to limit the effects of DoS attacks, a token taker SHOULD 638 limit the rate of QCD_TOKENs verified from a particular source. 640 If excessive amounts of IKE requests protected with unknown IKE SPIs 641 arrive at a token maker, the IKE module SHOULD revert to the behavior 642 described in section 2.21 of [RFC4306] and either send an 643 INVALID_IKE_SPI notification, or ignore it entirely. 645 9.2. Response to unknown child SPI 647 After a reboot, it is more likely that an implementation receives 648 IPsec packets than IKE packets. In that case, the rebooted 649 implementation will send an INVALID_SPI notification, triggering a 650 liveness check. The token will only be sent in a response to the 651 liveness check, thus requiring an extra round-trip. 653 To avoid this, an implementation that has access to non-volatile 654 storage MAY store a mapping of child SPIs to owning IKE SPIs, or to 655 generated tokens. If such a mapping is available and persistent 656 across reboots, the rebooted implementation SHOULD respond to the 657 IPsec packet with an INVALID_SPI notification, along with the 658 appropriate QCD_Token notifications. A token taker SHOULD verify the 659 QCD token that arrives with an INVALID_SPI notification the same as 660 if it arrived with the IKE SPIs of the parent IKE SA. 662 However, a persistent storage module might not be updated in a timely 663 manner, and could be populated with tokens relating to IKE SPIs that 664 have already been rekeyed. A token taker MUST NOT take an invalid 665 QCD Token sent along with an INVALID_SPI notification as evidence 666 that the peer is either malfunctioning or attacking, but it SHOULD 667 limit the rate at which such notifications are processed. 669 9.3. Using Tokens that Depend on IP Addresses 671 This section describes the rationale for token generation methods 672 such as the one described in Section 5.2. Note that this section 673 merely provides a possible rationale, and does not specify or 674 recommend any kind of configuration. 676 Some configurations of security gateway use a load-sharing cluster of 677 hosts, all sharing the same IP addresses, where the SAs (IKE and 678 child) are not synchronized between the cluster members. In such a 679 configuration, a single member does not know about all the IKE SAs 680 that are active for the configuration. A load balancer (usually a 681 networking switch) sends IKE and IPsec packets to the several members 682 based on source IP address. 684 In such a configuration, an attacker can send a forged protected IKE 685 packet with the IKE SPIs of an existing IKE SA, but from a different 686 IP address. This packet will likely be processed by a different 687 cluster member from the one that owns the IKE SA. Since no IKE SA 688 state is stored on this member, it will send a QCD token to the 689 attacker. If the QCD token does not depend on IP address, this token 690 can immediately be used to tell the token taker to tear down the IKE 691 SA using an unprotected QCD_TOKEN notification. 693 To thwart this possible attack, such configurations should use a 694 method that considers the taker's IP address, such as the method 695 described in Section 5.2. 697 10. Security Considerations 699 10.1. QCD Token Generation and Handling 701 Tokens MUST be hard to guess. This is critical, because if an 702 attacker can guess the token associated with an IKE SA, she can tear 703 down the IKE SA and associated tunnels at will. When the token is 704 delivered in the IKE_AUTH exchange, it is encrypted. When it is sent 705 again in an unprotected notification, it is not, but that is the last 706 time this token is ever used. 708 An aggregation of some tokens generated by one maker together with 709 the related IKE SPIs MUST NOT give an attacker the ability to guess 710 other tokens. Specifically, if one taker does not properly secure 711 the QCD tokens and an attacker gains access to them, this attacker 712 MUST NOT be able to guess other tokens generated by the same maker. 713 This is the reason that the QCD_SECRET in Section 5.1 needs to be 714 sufficiently long. 716 The token taker MUST store the token in a secure manner. No attacker 717 should be able to gain access to a stored token. 719 The QCD_SECRET MUST be protected from access by other parties. 720 Anyone gaining access to this value will be able to delete all the 721 IKE SAs for this token maker. 723 The QCD token is sent by the rebooted peer in an unprotected message. 724 A message like that is subject to modification, deletion and replay 725 by an attacker. However, these attacks will not compromise the 726 security of either side. Modification is meaningless because a 727 modified token is simply an invalid token. Deletion will only cause 728 the protocol not to work, resulting in a delay in tunnel re- 729 establishment as described in Section 2. Replay is also meaningless, 730 because the IKE SA has been deleted after the first transmission. 732 10.2. QCD Token Transmission 734 A token maker MUST NOT send a QCD token in an unprotected message for 735 an existing IKE SA. This implies that a conforming QCD token maker 736 MUST be able to tell whether a particular pair of IKE SPIs represent 737 a valid IKE SA. 739 This requirement is obvious and easy in the case of a single gateway. 740 However, some implementations use a load balancer to divide the load 741 between several physical gateways. It MUST NOT be possible even in 742 such a configuration to trick one gateway into sending a QCD token 743 for an IKE SA which is valid on another gateway. 745 This document does not specify how a load sharing sharing 746 configuration of IPsec gateways would work, but in order to support 747 this specification, all members MUST be able to tell whether a 748 particular IKE SA is active anywhere in the cluster. One way to do 749 it is to synchronize a list of active IKE SPIs among all the cluster 750 members. 752 10.3. QCD Token Enumeration 754 An attacker may try to attack QCD if the generation algorithm 755 described in Section 5.1 is used. The attacker will send several 756 fake IKE requests to the gateway under attack, receiving and 757 recording the QCD Tokens in the responses. This will allow the 758 attacker to create a dictionary of IKE SPIs to QCD Tokens, which can 759 later be used to tear down any IKE SA. 761 Three factors mitigate this threat: 762 o The space of all possible IKE SPI pairs is huge: 2^128, so making 763 such a dictionary is impractical. Even if we assume that one 764 implementation is faulty and always generates predictable IKE 765 SPIs, the space is still at least 2^64 entries, so making the 766 dictionary is extremely hard. 767 o Throttling the amount of QCD_TOKEN notifications sent out, as 768 discussed in Section 9.1, especially when not soon after a crash 769 will limit the attacker's ability to construct a dictionary. 770 o The methods in Section 5.1 and Section 5.2 allow for a periodic 771 change of the QCD_SECRET. Any such change invalidates the entire 772 dictionary. 774 11. IANA Considerations 776 IANA is requested to assign a notify message type from the status 777 types range (16406-40959) of the "IKEv2 Notify Message Types" 778 registry with name "QUICK_CRASH_DETECTION". 780 12. Acknowledgements 782 We would like to thank Hannes Tschofenig and Yaron Sheffer for their 783 comments about Session Resumption. 785 13. Change Log 787 This section lists all changes in this document 789 NOTE TO RFC EDITOR : Please remove this section in the final RFC 791 13.1. Changes from draft-nir-ike-qcd-03 and -04 793 Mostly editorial changes and cleaning up. 795 13.2. Changes from draft-nir-ike-qcd-02 797 o Described QCD token enumeration, following a question by 798 Lakshminath Dondeti. 799 o Added the ability to replace the QCD token for an existing IKE SA. 800 o Added tokens dependant on peer IP address and their interaction 801 with MOBIKE. 803 13.3. Changes from draft-nir-ike-qcd-01 805 o Removed stateless method. 806 o Added discussion of rekeying and resumption. 807 o Added discussion of non-synchronized load-balanced clusters of 808 gateways in the security considerations. 809 o Other wording fixes. 811 13.4. Changes from draft-nir-ike-qcd-00 813 o Merged proposal with draft-detienne-ikev2-recovery [recovery] 814 o Changed the protocol so that the rebooted peer generates the 815 token. This has the effect, that the need for persistent storage 816 is eliminated. 817 o Added discussion of birth certificates. 819 13.5. Changes from draft-nir-qcr-00 821 o Changed name to reflect that this relates to IKE. Also changed 822 from quick crash recovery to quick crash detection to avoid 823 confusion with IFARE. 824 o Added more operational considerations. 825 o Added interaction with IFARE. 826 o Added discussion of backup gateways. 828 14. References 830 14.1. Normative References 832 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 833 Requirement Levels", BCP 14, RFC 2119, March 1997. 835 [RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", 836 RFC 4306, December 2005. 838 [RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol 839 (MOBIKE)", RFC 4555, June 2006. 841 [RFC4718] Eronen, P. and P. Hoffman, "IKEv2 Clarifications and 842 Implementation Guidelines", RFC 4718, October 2006. 844 14.2. Informative References 846 [recovery] 847 Detienne, F., Sethi, P., and Y. Nir, "Safe IKE Recovery", 848 draft-detienne-ikev2-recovery (work in progress), 849 August 2008. 851 [resumption] 852 Sheffer, Y. and H. Tschofenig, "IKEv2 Session Resumption", 853 draft-ietf-ipsecme-ikev2-resumption (work in progress), 854 June 2009. 856 Authors' Addresses 858 Yoav Nir 859 Check Point Software Technologies Ltd. 860 5 Hasolelim st. 861 Tel Aviv 67897 862 Israel 864 Email: ynir@checkpoint.com 866 Frederic Detienne 867 Cisco Systems, Inc. 868 De Kleetlaan, 7 869 Diegem B-1831 870 Belgium 872 Phone: +32 2 704 5681 873 Email: fd@cisco.com 875 Pratima Sethi 876 Cisco Systems, Inc. 877 O'Shaugnessy Road, 11 878 Bangalore, Karnataka 560027 879 India 881 Phone: +91 80 4154 1654 882 Email: psethi@cisco.com