idnits 2.17.1 draft-ietf-ipsecme-failure-detection-06.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (March 10, 2011) is 4796 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) == Missing Reference: 'IDr' is mentioned on line 309, but not defined == Missing Reference: 'KEi' is mentioned on line 368, but not defined == Missing Reference: 'KEr' is mentioned on line 370, but not defined == Missing Reference: 'CERTREQ' is mentioned on line 591, but not defined ** Obsolete normative reference: RFC 5996 (Obsoleted by RFC 7296) Summary: 1 error (**), 0 flaws (~~), 5 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IPsecME Working Group Y. Nir, Ed. 3 Internet-Draft Check Point 4 Intended status: Standards Track D. Wierbowski 5 Expires: September 11, 2011 IBM 6 F. Detienne 7 P. Sethi 8 Cisco 9 March 10, 2011 11 A Quick Crash Detection Method for IKE 12 draft-ietf-ipsecme-failure-detection-06 14 Abstract 16 This document describes an extension to the IKEv2 protocol that 17 allows for faster detection of SA desynchronization using a saved 18 token. 20 When an IPsec tunnel between two IKEv2 peers is disconnected due to a 21 restart of one peer, it can take as much as several minutes for the 22 other peer to discover that the reboot has occurred, thus delaying 23 recovery. In this text we propose an extension to the protocol, that 24 allows for recovery immediately following the restart. 26 Status of this Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at http://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on September 11, 2011. 43 Copyright Notice 45 Copyright (c) 2011 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (http://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 61 1.1. Conventions Used in This Document . . . . . . . . . . . . 4 62 2. RFC 5996 Crash Recovery . . . . . . . . . . . . . . . . . . . 5 63 3. Protocol Outline . . . . . . . . . . . . . . . . . . . . . . . 6 64 4. Formats and Exchanges . . . . . . . . . . . . . . . . . . . . 7 65 4.1. Notification Format . . . . . . . . . . . . . . . . . . . 7 66 4.2. Passing a Token in the AUTH Exchange . . . . . . . . . . 8 67 4.3. Replacing Tokens After Rekey or Resumption . . . . . . . 9 68 4.4. Replacing the Token for an Existing SA . . . . . . . . . 10 69 4.5. Presenting the Token in an Unprotected Message . . . . . 10 70 5. Token Generation and Verification . . . . . . . . . . . . . . 11 71 5.1. A Stateless Method of Token Generation . . . . . . . . . 11 72 5.2. A Stateless Method with IP addresses . . . . . . . . . . 12 73 5.3. Token Lifetime . . . . . . . . . . . . . . . . . . . . . 12 74 6. Backup Gateways . . . . . . . . . . . . . . . . . . . . . . . 12 75 7. Interaction with Session Resumption . . . . . . . . . . . . . 13 76 8. Operational Considerations . . . . . . . . . . . . . . . . . . 14 77 8.1. Who should implement this specification . . . . . . . . . 14 78 8.2. Response to unknown child SPI . . . . . . . . . . . . . . 15 79 9. Security Considerations . . . . . . . . . . . . . . . . . . . 16 80 9.1. QCD Token Generation and Handling . . . . . . . . . . . . 16 81 9.2. QCD Token Transmission . . . . . . . . . . . . . . . . . 17 82 9.3. QCD Token Enumeration . . . . . . . . . . . . . . . . . . 17 83 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 84 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18 85 12. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 18 86 12.1. Changes from draft-ietf-ipsecme-failure-detection-05 . . 18 87 12.2. Changes from draft-ietf-ipsecme-failure-detection-04 . . 19 88 12.3. Changes from draft-ietf-ipsecme-failure-detection-03 . . 19 89 12.4. Changes from draft-ietf-ipsecme-failure-detection-02 . . 19 90 12.5. Changes from draft-ietf-ipsecme-failure-detection-01 . . 19 91 12.6. Changes from draft-ietf-ipsecme-failure-detection-00 . . 19 92 12.7. Changes from draft-nir-ike-qcd-07 . . . . . . . . . . . . 19 93 12.8. Changes from draft-nir-ike-qcd-03 and -04 . . . . . . . . 20 94 12.9. Changes from draft-nir-ike-qcd-02 . . . . . . . . . . . . 20 95 12.10. Changes from draft-nir-ike-qcd-01 . . . . . . . . . . . . 20 96 12.11. Changes from draft-nir-ike-qcd-00 . . . . . . . . . . . . 20 97 12.12. Changes from draft-nir-qcr-00 . . . . . . . . . . . . . . 20 98 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21 99 13.1. Normative References . . . . . . . . . . . . . . . . . . 21 100 13.2. Informative References . . . . . . . . . . . . . . . . . 21 101 Appendix A. The Path Not Taken . . . . . . . . . . . . . . . . . 21 102 A.1. Initiating a new IKE SA . . . . . . . . . . . . . . . . . 21 103 A.2. SIR . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 104 A.3. Birth Certificates . . . . . . . . . . . . . . . . . . . 22 105 A.4. Reducing Liveness Check Length . . . . . . . . . . . . . 22 106 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23 108 1. Introduction 110 IKEv2, as described in [RFC5996] and its predecessor RFC 4306, has a 111 method for recovering from a reboot of one peer. As long as traffic 112 flows in both directions, the rebooted peer should re-establish the 113 tunnels immediately. However, in many cases the rebooted peer is a 114 VPN gateway that protects only servers, so all traffic is inbound. 115 In other cases, the non-rebooted peer has a dynamic IP address, so 116 the rebooted peer cannot initiate IKE because its current IP address 117 is unknown. In such cases, the rebooted peer will not be able to re- 118 establish the tunnels. Section 2 describes how recovery works under 119 RFC 5996, and explains why it may take several minutes. 121 The method proposed here, is to send an octet string, called a "QCD 122 token" in the IKE_AUTH exchange that establishes the tunnel. That 123 token can be stored on the peer as part of the IKE SA. After a 124 reboot, the rebooted implementation can re-generate the token, and 125 send it to the peer, so as to delete the IKE SA. Deleting the IKE SA 126 results in a quick establishment of new IPsec tunnels. This is 127 described in Section 3. 129 1.1. Conventions Used in This Document 131 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 132 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 133 document are to be interpreted as described in [RFC2119]. 135 The term "token" refers to an octet string that an implementation can 136 generate using only the properties of a protected IKE message (such 137 as IKE SPIs) as input. A conforming implementation MUST be able to 138 generate the same token from the same input even after rebooting. 140 The term "token maker" refers to an implementation that generates a 141 token and sends it to the peer as specified in this document. 143 The term "token taker" refers to an implementation that stores such a 144 token or a digest thereof, in order to verify that a new token it 145 receives is identical to the old token it has stored. 147 The term "non-volatile storage" in this document refers to a data 148 storage module, that persists across restarts of the token maker. 149 Examples of such a storage module include an internal disk, an 150 internal flash memory module, an external disk and an external 151 database. A small non-volatile storage module is required for a 152 token maker, but a larger one can be used to enhance performance, as 153 described in Section 8.2. 155 2. RFC 5996 Crash Recovery 157 When one peer loses state or reboots, the other peer does not get any 158 notification, so unidirectional IPsec traffic can still flow. The 159 rebooted peer will not be able to decrypt it, however, and the only 160 remedy is to send an unprotected INVALID_SPI notification as 161 described in section 3.10.1 of [RFC5996]. That section also 162 describes the processing of such a notification: 164 "If this Informational Message is sent outside the 165 context of an IKE_SA, it should be used by the recipient 166 only as a "hint" that something might be wrong (because it 167 could easily be forged)." 169 Since the INVALID_SPI can only be used as a hint, the non-rebooted 170 peer has to determine whether the IPsec SA, and indeed the parent IKE 171 SA are still valid. The method of doing this is described in section 172 2.4 of [RFC5996]. This method, called "liveness check" involves 173 sending a protected empty INFORMATIONAL message, and awaiting a 174 response. This procedure is sometimes referred to as "Dead Peer 175 Detection" or DPD. 177 Section 2.4 does not mandate how many times the liveness check 178 message should be retransmitted, or for how long, but does recommend 179 the following: 181 "It is 182 suggested that messages be retransmitted at least a dozen times over 183 a period of at least several minutes before giving up on an SA..." 185 Those "at least several minutes" are a time during part of which both 186 peers are active, but IPsec cannot be used. 188 Especially in the case of a reboot (rather than fail-over or 189 administrative clearing of state), the peer does not recover 190 immediately. Reboot, depending on the system, may take from a few 191 seconds to a few minutes. This means that at first the peer just 192 goes silent, i.e., does not send or respond to any messages. IKEv2 193 implementations can detect this situation and follow the rules given 194 in section 2.4: 196 If there has only been outgoing traffic on all of 197 the SAs associated with an IKE SA, it is essential to confirm 198 liveness of the other endpoint to avoid black holes. If no 199 cryptographically protected messages have been received on an IKE 200 SA or any of its Child SAs recently, the system needs to perform a 201 liveness check in order to prevent sending messages to a dead peer. 203 [RFC5996] does not mandate any time limits, but it is possible that 204 the peer will start liveness checks even before the other end is 205 sending INVALID_SPI notification, as it detected that the other end 206 is not sending any packets anymore while it is still rebooting or 207 recovering from the situation. 209 This means that the several minutes recovery period is overlaping the 210 actual recover time of the other peer, i.e., if the security gateway 211 requires several minutes to boot up from the crash then the other 212 peers have already finished their liveness checks before the crashing 213 peer even has a chance to send INVALID_SPI notifications. 215 There are cases where the peer loses state and is able to recover 216 immediately; in those cases it might take several minutes to recreate 217 the IPsec SAs. 219 Note that the IKEv2 specification specifically gives no guidance for 220 the number of retries or the length of timeouts, as these do not 221 affect interoperability. This means that implementations are allowed 222 to use the hints provided by the INVALID_SPI messages to shorten 223 those timeouts (i.e., different environment and situation requiring 224 different rules). 226 Some existing IKEv2 implementations already do that (i.e., both 227 shorten timeouts or limit number of retries) based on these kind of 228 hints and also start liveness checks quickly after the other end goes 229 silent. However, see Appendix A.4 for a discussion of why this may 230 not be enough. 232 3. Protocol Outline 234 Supporting implementations will send a notification, called a "QCD 235 token", as described in Section 4.1 in the first IKE_AUTH exchange 236 messages. These are the first IKE_AUTH request and final IKE_AUTH 237 response that contain the AUTH payloads. The generation of these 238 tokens is a local matter for implementations, but considerations are 239 described in Section 5. Implementations that send such a token will 240 be called "token makers". 242 A supporting implementation receiving such a token MUST store it (or 243 a digest thereof) along with the IKE SA. Implementations that 244 support this part of the protocol will be called "token takers". 245 Section 8.1 has considerations for which implementations need to be 246 token takers, and which should be token makers. Implementations that 247 are not token takers will silently ignore QCD tokens. 249 When a token maker receives a protected IKE request message with 250 unknown IKE SPIs, it SHOULD generate a new token that is identical to 251 the previous token, and send it to the requesting peer in an 252 unprotected IKE message as described in Section 4.5. 254 When a token taker receives the QCD token in an unprotected 255 notification, it MUST verify that the TOKEN_SECRET_DATA matches the 256 token stored with the matching IKE SA. If the verification fails, or 257 if the IKE SPIs in the message do not match any existing IKE SA, it 258 SHOULD log the event. If it succeeds, it MUST silently delete the 259 IKE SA associated with the IKE_SPI fields, and all dependent child 260 SAs. This event MAY also be logged. The token taker MUST accept 261 such tokens from any IP address and port combination, so as to allow 262 different kinds of high-availability configurations of the token 263 maker. 265 A supporting token taker MAY immediately create new SAs using an 266 Initial exchange, or it may wait for subsequent traffic to trigger 267 the creation of new SAs. 269 See Section 7 for a short discussion about this extensions's 270 interaction with IKEv2 Session Resumption ([RFC5723]). 272 4. Formats and Exchanges 274 4.1. Notification Format 276 The notification payload called "QCD token" is formatted as follows: 278 1 2 3 279 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 1 280 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 281 ! Next Payload !C! RESERVED ! Payload Length ! 282 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 283 ! Protocol ID ! SPI Size ! QCD Token Notify Message Type ! 284 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 285 ! ! 286 ~ TOKEN_SECRET_DATA ~ 287 ! ! 288 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 290 o Protocol ID (1 octet) MUST be 1, as this message is related to an 291 IKE SA. 292 o SPI Size (1 octet) MUST be zero, in conformance with section 3.10 293 of [RFC5996]. 294 o QCD Token Notify Message Type (2 octets) - MUST be xxxxx, the 295 value assigned for QCD token notifications. TBA by IANA. 297 o TOKEN_SECRET_DATA (variable) contains a generated token as 298 described in Section 5. 300 4.2. Passing a Token in the AUTH Exchange 302 For brevity, only the EAP version of an AUTH exchange will be 303 presented here. The non-EAP version is very similar. The figures 304 below are based on appendix C.3 of [RFC5996]. 306 first request --> IDi, 307 [N(INITIAL_CONTACT)], 308 [[N(HTTP_CERT_LOOKUP_SUPPORTED)], CERTREQ+], 309 [IDr], 310 [N(QCD_TOKEN)] 311 [CP(CFG_REQUEST)], 312 [N(IPCOMP_SUPPORTED)+], 313 [N(USE_TRANSPORT_MODE)], 314 [N(ESP_TFC_PADDING_NOT_SUPPORTED)], 315 [N(NON_FIRST_FRAGMENTS_ALSO)], 316 SA, TSi, TSr, 317 [V+] 319 first response <-- IDr, [CERT+], AUTH, 320 EAP, 321 [V+] 323 / --> EAP 324 repeat 1..N times | 325 \ <-- EAP 327 last request --> AUTH 329 last response <-- AUTH, 330 [N(QCD_TOKEN)] 331 [CP(CFG_REPLY)], 332 [N(IPCOMP_SUPPORTED)], 333 [N(USE_TRANSPORT_MODE)], 334 [N(ESP_TFC_PADDING_NOT_SUPPORTED)], 335 [N(NON_FIRST_FRAGMENTS_ALSO)], 336 SA, TSi, TSr, 337 [N(ADDITIONAL_TS_POSSIBLE)], 338 [V+] 340 Note that the QCD_TOKEN notification is marked as optional because it 341 is not required by this specification that every implementation be 342 both token maker and token taker. If only one peer sends the QCD 343 token, then a reboot of the other peer will not be recoverable by 344 this method. This may be acceptable if traffic typically originates 345 from the other peer. 347 In any case, the lack of a QCD_TOKEN notification MUST NOT be taken 348 as an indication that the peer does not support this standard. 349 Conversely, if a peer does not understand this notification, it will 350 simply ignore it. Therefore a peer may send this notification 351 freely, even if it does not know whether the other side supports it. 353 The QCD_TOKEN notification is related to the IKE SA and should follow 354 the AUTH payload and precede the Configuration payload and all 355 payloads related to the child SA. 357 4.3. Replacing Tokens After Rekey or Resumption 359 After rekeying an IKE SA, the IKE SPIs are replaced, so the new SA 360 also needs to have a token. If only the responder in the rekey 361 exchange is the token maker, this can be done within the 362 CREATE_CHILD_SA exchange. If the initiator is a token maker, then we 363 need an extra informational exchange. 365 The following figure shows the CREATE_CHILD_SA exchange for rekeying 366 the IKE SA. Only the responder sends a QCD token. 368 request --> SA, Ni, [KEi] 370 response <-- SA, Nr, [KEr], N(QCD_TOKEN) 372 If the initiator is also a token maker, it SHOULD initiate an 373 INFORMATIONAL exchange immediately after the CREATE_CHILD_SA exchange 374 as follows: 376 request --> N(QCD_TOKEN) 378 response <-- 380 For session resumption, as specified in [RFC5723], the situation is 381 similar. The responder, which is necessarily the peer that has 382 crashed, SHOULD send a new ticket within the protected payload of the 383 IKE_SESSION_RESUME exchange. If the Initiator is also a token maker, 384 it needs to send a QCD_TOKEN in a separate INFORMATIONAL exchange. 386 The INFORMATIONAL exchange described in this section can also be used 387 if QCD tokens need to be replaced due to a key rollover. However, 388 since token takers are required to verify at least 4 QCD tokens, this 389 is only necessary if secret QCD keys are rolled over more than four 390 times as often as IKE SAs are rekeyed. See Section 5.1 for an 391 example method that uses secret keys which may require rollover. 393 4.4. Replacing the Token for an Existing SA 395 With some token generation methods, such as that described in 396 Section 5.2, a QCD token may sometimes become invalid, although the 397 IKE SA is still perfectly valid. 399 In such a case, the token maker MUST send the new token in a 400 protected message under that IKE SA. That exchange could be a simple 401 INFORMATIONAL, such as in the last figure in the previous section, or 402 else it can be part of a MOBIKE INFORMATIONAL exchange such as in the 403 following figure taken from section 2.2 of [RFC4555] and modified by 404 adding a QCD_TOKEN notification: 406 (IP_I2:4500 -> IP_R1:4500) 407 HDR, SK { N(UPDATE_SA_ADDRESSES), 408 N(NAT_DETECTION_SOURCE_IP), 409 N(NAT_DETECTION_DESTINATION_IP) } --> 411 <-- (IP_R1:4500 -> IP_I2:4500) 412 HDR, SK { N(NAT_DETECTION_SOURCE_IP), 413 N(NAT_DETECTION_DESTINATION_IP) } 415 <-- (IP_R1:4500 -> IP_I2:4500) 416 HDR, SK { N(COOKIE2), [N(QCD_TOKEN)] } 418 (IP_I2:4500 -> IP_R1:4500) 419 HDR, SK { N(COOKIE2), [N(QCD_TOKEN)] } --> 421 A token taker MUST accept such gratuitous QCD_TOKEN notifications as 422 long as they are carried in protected exchanges. A token maker 423 SHOULD NOT generate them unless it is no longer able to generate the 424 old QCD_TOKEN. 426 4.5. Presenting the Token in an Unprotected Message 428 This QCD_TOKEN notification is unprotected, and is sent as a response 429 to a protected IKE request, which uses an IKE SA that is unknown. 431 message --> N(INVALID_IKE_SPI), N(QCD_TOKEN)+ 433 If child SPIs are persistently mapped to IKE SPIs as described in 434 Section 8.2, a token taker may get the following unprotected message 435 in response to an ESP or AH packet. 437 message --> N(INVALID_SPI), N(QCD_TOKEN)+ 439 The QCD_TOKEN and INVALID_IKE_SPI notifications are sent together to 440 support both implementations that conform to this specification and 441 implementations that don't. Similar to the description in section 442 2.21 of [RFC5996], the IKE SPI and message ID fields in the packet 443 headers are taken from the protected IKE request. 445 To support a periodic rollover of the secret used for token 446 generation, the token taker MUST support at least four QCD_TOKEN 447 notifications in a single packet. The token is considered verified 448 if any of the QCD_TOKEN notifications matches. The token maker MAY 449 generate up to four QCD_TOKEN notifications, based on several 450 generations of keys. 452 If the QCD_TOKEN verifies OK, the receiver MUST silently discard the 453 IKE SA and all associated child SAs. If the QCD_TOKEN cannot be 454 validated, a response MUST NOT be sent, and the event may be logged. 455 Section 5 defines token verification. 457 5. Token Generation and Verification 459 No token generation method is mandated by this document. Two methods 460 are documented in the following sub-sections, but they only serve as 461 examples. 463 The following lists the requirements for a token generation 464 mechanism: 465 o Tokens MUST be at least 16 octets long, and no more than 128 466 octets long, to facilitate storage and transmission. Tokens 467 SHOULD be indistinguishable from random data. 468 o It should not be possible for an external attacker to guess the 469 QCD token generated by an implementation. Cryptographic 470 mechanisms such as PRNG and hash functions are RECOMMENDED. 471 o The token maker MUST be able to re-generate or retrieve the token 472 based on the IKE SPIs even after it reboots. 473 o The method of token generation MUST be such that a collision of 474 QCD tokens between different pairs of IKE SPI will be highly 475 unlikely. 477 5.1. A Stateless Method of Token Generation 479 The following describes a stateless method of generating a token. In 480 this case, 'stateless' means not maintaining any per-tunnel state, 481 although there is a small amount of non-volatile storage required. 482 o At installation or immediately after the first boot of the token 483 maker, 32 random octets are generated using a secure random number 484 generator or a PRNG. 485 o Those 32 bytes, called the "QCD_SECRET", are stored in non- 486 volatile storage on the machine, and kept indefinitely. 488 o If key rollover is required by policy, the implementation MAY 489 periodically generate a new QCD_SECRET and keep up to 3 previous 490 generations. When sending an unprotected QCD_TOKEN, as many as 4 491 notification payloads may be sent, each from a different 492 QCD_SECRET. 493 o The TOKEN_SECRET_DATA is calculated as follows: 495 TOKEN_SECRET_DATA = HASH(QCD_SECRET | SPI-I | SPI-R) 497 5.2. A Stateless Method with IP addresses 499 This method is similar to the one in the previous section, except 500 that the IP address of the token taker is also added to the block 501 being hashed. This has the disadvantage that the token needs to be 502 replaced (as described in Section 4.4) whenever the token taker 503 changes its address. 505 See Section 9.2 for a discussion of a use-case for this method. When 506 using this method, the TOKEN_SECRET_DATA field is calculated as 507 follows: 509 TOKEN_SECRET_DATA = HASH(QCD_SECRET | SPI-I | SPI-R | IPaddr-T) 511 The IPaddr-T field specifies the IP address of the token taker. 512 Secret rollover considerations are similar to those in the previous 513 section. 515 5.3. Token Lifetime 517 The token is associated with a single IKE SA, and SHOULD be deleted 518 by the token taker when the SA is deleted or expires. More formally, 519 the token is associated with the pair (SPI-I, SPI-R). 521 6. Backup Gateways 523 Making crash detection and recovery quick is a worthy goal, but since 524 rebooting a gateway takes a non-zero amount of time, many 525 implementations choose to have a stand-by gateway ready to take over 526 as soon as the primary gateway fails for any reason. [cluster] 527 describes considerations for such clusters of gateways with 528 synchronized state, but the rest of this section is relevant even 529 when there is no synchronized state. 531 If such a configuration is available, it is RECOMMENDED that the 532 stand-by gateway be able to generate the same token as the active 533 gateway. if the method described in Section 5.1 is used, this means 534 that the QCD_SECRET field is identical in both gateways. This has 535 the effect of having the crash recovery available immediately. 537 Note that this refers to "high availability" configurations, where 538 only one gateway is active at any given moment. This is different 539 from "load sharing" configurations where more than one gateway is 540 active at the same time. For load sharing configurations, please see 541 Section 9.2 for security considerations. 543 7. Interaction with Session Resumption 545 Session resumption, specified in [RFC5723], allows the setting up of 546 a new IKE SA to consume less computing resources. This is 547 particularly useful in the case of a remote access gateway that has 548 many tunnels. A failure of such a gateway requires all these many 549 remote access clients to establish an IKE SA either with the rebooted 550 gateway or with a backup. This tunnel re-establishment occurs within 551 a short period of time, creating a burden on the remote access 552 gateway. Session resumption addresses this problem by having the 553 clients store an encrypted derivative of the IKE SA for quick re- 554 establishment. 556 What Session Resumption does not help is the problem of detecting 557 that the peer gateway has failed. A failed gateway may go undetected 558 for an arbitrarily long time, because IPsec does not have packet 559 acknowledgement, and applications cannot signal the IPsec layer that 560 the tunnel "does not work". Section 2.4 of RFC 5996 does not specify 561 how long an implementation needs to wait before beginning a liveness 562 check, and only says "not recently" (see full quote in Section 2). 563 In practice some mobile devices wait a very long time before 564 beginning liveness check, in order to extend battery life by allowing 565 parts of the device to remain in low-power modes. 567 QCD tokens provide a way to detect the failure of the peer in the 568 case where liveness check has not yet ended (or begun). 570 A remote access client conforming to both specifications will store 571 QCD tokens, as well as the Session Resumption ticket, if provided by 572 the gateway. A remote access gateway conforming to both 573 specifications will generate a QCD token for the client. When the 574 gateway reboots, the client will discover this in either of two ways: 575 1. The client does regular liveness checks, or else the time for 576 some other IKE exchange has come. Since the gateway is still 577 down, the IKE exchange times out after several minutes. In this 578 case QCD does not help. 579 2. Either the primary gateway or a backup gateway (see Section 6) is 580 ready and sends a QCD token to the client. In that case the 581 client will quickly re-establish the IPsec tunnel, either with 582 the rebooted primary gateway or the backup gateway as described 583 in this document. 585 The full combined protocol looks like this: 587 Initiator Responder 588 ----------- ----------- 589 HDR, SAi1, KEi, Ni --> 591 <-- HDR, SAr1, KEr, Nr, [CERTREQ] 593 HDR, SK {IDi, [CERT,] 594 [CERTREQ,] [IDr,] 595 AUTH, N(QCD_TOKEN) 596 SAi2, TSi, TSr, 597 N(TICKET_REQUEST)} --> 598 <-- HDR, SK {IDr, [CERT,] AUTH, 599 N(QCD_TOKEN), SAr2, TSi, TSr, 600 N(TICKET_LT_OPAQUE) } 602 ---- Reboot ----- 604 HDR, {} --> 605 <-- HDR, N(QCD_TOKEN) 607 HDR, [N(COOKIE),] 608 Ni, N(TICKET_OPAQUE) 609 [,N+] --> 610 <-- HDR, Nr [,N+] 612 8. Operational Considerations 614 8.1. Who should implement this specification 616 Throughout this document, we have referred to reboot time 617 alternatingly as the time that the implementation crashes and the 618 time when it is ready to process IPsec packets and IKE exchanges. 619 Depending on the hardware and software platforms and the cause of the 620 reboot, rebooting may take anywhere from a few seconds to several 621 minutes. If the implementation is down for a long time, the benefit 622 of this protocol extension is reduced. For this reason critical 623 systems should implement backup gateways as described in Section 6. 625 Implementing the "token maker" side of QCD makes sense for IKE 626 implementation where protected connections originate from the peer, 627 such as inter-domain VPNs and remote access gateways. Implementing 628 the "token taker" side of QCD makes sense for IKE implementations 629 where protected connections originate, such as inter-domain VPNs and 630 remote access clients. 632 To clarify the this discussion: 633 o For remote-access clients it makes sense to implement the token 634 taker role. 635 o For remote-access gateways it makes sense to implement the token 636 maker role. 637 o For inter-domain VPN gateways it makes sense to implement both 638 roles, because it can't be known in advance where the traffic 639 originates. 640 o It is perfectly valid to implement both roles in any case, for 641 example when using a single library or a single gateway to perform 642 several roles. 644 In order to limit the effects of DoS attacks, a token taker SHOULD 645 limit the rate of QCD_TOKENs verified from a particular source. 647 If excessive amounts of IKE requests protected with unknown IKE SPIs 648 arrive at a token maker, the IKE module SHOULD revert to the behavior 649 described in section 2.21 of [RFC5996] and either send an 650 INVALID_IKE_SPI notification, or ignore it entirely. 652 8.2. Response to unknown child SPI 654 After a reboot, it is more likely that an implementation receives 655 IPsec packets than IKE packets. In that case, the rebooted 656 implementation will send an INVALID_SPI notification, triggering a 657 liveness check. The token will only be sent in a response to the 658 liveness check, thus requiring an extra round-trip. 660 To avoid this, an implementation that has access to enough non- 661 volatile storage MAY store a mapping of child SPIs to owning IKE 662 SPIs, or to generated tokens. If such a mapping is available and 663 persistent across reboots, the rebooted implementation SHOULD respond 664 to the IPsec packet with an INVALID_SPI notification, along with the 665 appropriate QCD_Token notifications. A token taker SHOULD verify the 666 QCD token that arrives with an INVALID_SPI notification the same as 667 if it arrived with the IKE SPIs of the parent IKE SA. 669 However, a persistent storage module might not be updated in a timely 670 manner, and could be populated with tokens relating to IKE SPIs that 671 have already been rekeyed. A token taker MUST NOT take an invalid 672 QCD Token sent along with an INVALID_SPI notification as evidence 673 that the peer is either malfunctioning or attacking, but it SHOULD 674 limit the rate at which such notifications are processed. 676 9. Security Considerations 678 The extension described in this document must not reduce the security 679 of IKEv2 or IPsec. Specifically, an eavesdropper must not learn any 680 non-public information about the peers. 682 The proposed mechanism should be secure against attacks by a passive 683 MITM (eavesdropper). Such an attacker must not be able to disrupt an 684 existing IKE session, either by resetting the session or by 685 introducing significant delays. This requirement is especially 686 significant, because this document introduces a new way to reset an 687 IKE SA. 689 The mechanism need not be similarly secure against an active MITM, 690 since this type of attacker is already able to disrupt IKE sessions. 692 9.1. QCD Token Generation and Handling 694 Tokens MUST be hard to guess. This is critical, because if an 695 attacker can guess the token associated with an IKE SA, she can tear 696 down the IKE SA and associated tunnels at will. When the token is 697 delivered in the IKE_AUTH exchange, it is encrypted. When it is sent 698 again in an unprotected notification, it is not, but that is the last 699 time this token is ever used. 701 An aggregation of some tokens generated by one maker together with 702 the related IKE SPIs MUST NOT give an attacker the ability to guess 703 other tokens. Specifically, if one taker does not properly secure 704 the QCD tokens and an attacker gains access to them, this attacker 705 MUST NOT be able to guess other tokens generated by the same maker. 706 This is the reason that the QCD_SECRET in Section 5.1 needs to be 707 sufficiently long. 709 The token taker MUST store the token in a secure manner. No attacker 710 should be able to gain access to a stored token. 712 The QCD_SECRET MUST be protected from access by other parties. 713 Anyone gaining access to this value will be able to delete all the 714 IKE SAs for this token maker. 716 The QCD token is sent by the rebooted peer in an unprotected message. 717 A message like that is subject to modification, deletion and replay 718 by an attacker. However, these attacks will not compromise the 719 security of either side. Modification is meaningless because a 720 modified token is simply an invalid token. Deletion will only cause 721 the protocol not to work, resulting in a delay in tunnel re- 722 establishment as described in Section 2. Replay is also meaningless, 723 because the IKE SA has been deleted after the first transmission. 725 9.2. QCD Token Transmission 727 A token maker MUST NOT send a valid QCD token in an unprotected 728 message for an existing IKE SA. 730 This requirement is obvious and easy in the case of a single gateway. 731 However, some implementations use a load balancer to divide the load 732 between several physical gateways. It MUST NOT be possible even in 733 such a configuration to trick one gateway into sending a valid QCD 734 token for an IKE SA which is valid on another gateway. This is true 735 whether the attempt to trick the gateway uses the token taker's IP 736 address or a different IP address. 738 IPsec Failure Detection is not applicable to deployments where the 739 QCD secret is shared by multiple gateways and the gateways cannot 740 assess whether the token can be legitimately sent in the clear while 741 another gateway may actually still own the SA's. Load balancer 742 configurations typically fall in this category. In order for a load 743 balancing configuration of IPsec gateways to support this 744 specification, all members MUST be able to tell whether a particular 745 IKE SA is active anywhere in the cluster. One way to do it is to 746 synchronize a list of active IKE SPIs among all the cluster members. 748 Because it includes the token taker's IP address in the token 749 generation, the method in Section 5.2 can (under certain conditions) 750 prevent revealing the QCD token for an existing pair of IKE SPIs to 751 an attacker who is using a different IP address, even in a load- 752 sharing cluster without state synchronization. That method does not 753 prevent revealing the QCD token to an active attacker who is spoofing 754 the token taker's IP address. Such an attacker may attempt to direct 755 messages to a cluster member other than the member responsible for 756 the IKE SA in an attempt to trick that gateway into sending a QCD 757 token for a valid IKE SA. That method should not be used unless the 758 load balancer guarantees that IKE packets from the same source IP 759 address always go to the same cluster member. 761 9.3. QCD Token Enumeration 763 An attacker may try to attack QCD if the generation algorithm 764 described in Section 5.1 is used. The attacker will send several 765 fake IKE requests to the gateway under attack, receiving and 766 recording the QCD Tokens in the responses. This will allow the 767 attacker to create a dictionary of IKE SPIs to QCD Tokens, which can 768 later be used to tear down any IKE SA. 770 Three factors mitigate this threat: 771 o The space of all possible IKE SPI pairs is huge: 2^128, so making 772 such a dictionary is impractical. Even if we assume that one 773 implementation always generates predictable IKE SPIs, the space is 774 still at least 2^64 entries, so making the dictionary is extremely 775 hard. To ensure this, token makers MUST generate unpredictable 776 IKE SPIs by using a cryptographically strong pseudo-random number 777 generator. 778 o Throttling the amount of QCD_TOKEN notifications sent out, as 779 discussed in Section 8.1, especially when not soon after a crash 780 will limit the attacker's ability to construct a dictionary. 781 o The methods in Section 5.1 and Section 5.2 allow for a periodic 782 change of the QCD_SECRET. Any such change invalidates the entire 783 dictionary. 785 10. IANA Considerations 787 IANA is requested to assign a notify message type from the status 788 types range (16406-40959) of the "IKEv2 Notify Message Types" 789 registry with name "QUICK_CRASH_DETECTION". 791 11. Acknowledgements 793 We would like to thank Hannes Tschofenig and Yaron Sheffer for their 794 comments about Session Resumption. 796 Others who have contributed valuable comments are, in alphabetical 797 order, Lakshminath Dondeti, Paul Hoffman, Tero Kivinen, Scott C 798 Moonen, Magnus Nystrom, and Keith Welter. 800 12. Change Log 802 This section lists all changes in this document 804 NOTE TO RFC EDITOR : Please remove this section in the final RFC 806 12.1. Changes from draft-ietf-ipsecme-failure-detection-05 808 o Some clarifications suggested by Magnus Nystrom. 810 12.2. Changes from draft-ietf-ipsecme-failure-detection-04 812 o Some more rephrasing of section 9.2 based on suggestions by Tero 813 Kivinen and Dave Wierbowski. 815 12.3. Changes from draft-ietf-ipsecme-failure-detection-03 817 o Merged section 9.4 into section 9.2. 818 o Multiple typos discovered by Scott Moonen, Keith Welter and Yaron. 820 12.4. Changes from draft-ietf-ipsecme-failure-detection-02 822 o Moved section 7 to Appendix A. Also changed some wording. 823 o Fixed some language in the "interaction with session resumption" 824 section to say that although liveness check MUST be done, there 825 are no time limits to how long an implementation takes before 826 starting liveness check, or ending it. 828 12.5. Changes from draft-ietf-ipsecme-failure-detection-01 830 o Fixed the language requiring random IKE SPIs. 831 o Some better explanation of the reasons to choose the methods in 832 Section 5.2 and the method in Section 5.1, to close issue #193. 833 o Added text to the beginning of Section 9 to accomodate issue #194. 835 12.6. Changes from draft-ietf-ipsecme-failure-detection-00 837 o Nits pointed out by Scott and Yaron. 838 o Pratima and Frederic are back on board. 839 o Changed IKEv2bis draft reference to RFC 5996. 840 o Resolved issues #189, #190, #191, and #192: 841 * Renamed section 4.5 and removed the requirement to send an 842 acknowledgement for the unprotected message. 843 * Moved the QCD token from the last to the first IKE_AUTH 844 request. 845 * Added a MUST to Section 9.3 to require that IKE SPIs be 846 randomly generated. 847 * Changed the language in Section 8.1, to not use RFC 2119 848 terminology. 849 * Moved the section describing why one would want the method 850 dependant on IP addresses (in Section 5.2 from operational 851 considerations to security considerations. 853 12.7. Changes from draft-nir-ike-qcd-07 855 o First WG version. 857 o Addressed Scott C Moonen's concern about collisions of QCD tokens. 858 o Updated references to point to IKEv2bis instead of RFC 4306 and 859 4718. Also converted draft reference for resumption to RFC 5723. 860 o Added Dave Wiebrowski as author, and removed Pratima and Frederic. 862 12.8. Changes from draft-nir-ike-qcd-03 and -04 864 Mostly editorial changes and cleaning up. 866 12.9. Changes from draft-nir-ike-qcd-02 868 o Described QCD token enumeration, following a question by 869 Lakshminath Dondeti. 870 o Added the ability to replace the QCD token for an existing IKE SA. 871 o Added tokens dependent on peer IP address and their interaction 872 with MOBIKE. 874 12.10. Changes from draft-nir-ike-qcd-01 876 o Removed stateless method. 877 o Added discussion of rekeying and resumption. 878 o Added discussion of non-synchronized load-balanced clusters of 879 gateways in the security considerations. 880 o Other wording fixes. 882 12.11. Changes from draft-nir-ike-qcd-00 884 o Merged proposal with draft-detienne-ikev2-recovery 885 o Changed the protocol so that the rebooted peer generates the 886 token. This has the effect, that the need for persistent storage 887 is eliminated. 888 o Added discussion of birth certificates. 890 12.12. Changes from draft-nir-qcr-00 892 o Changed name to reflect that this relates to IKE. Also changed 893 from quick crash recovery to quick crash detection to avoid 894 confusion with IFARE. 895 o Added more operational considerations. 896 o Added interaction with IFARE. 897 o Added discussion of backup gateways. 899 13. References 900 13.1. Normative References 902 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 903 Requirement Levels", BCP 14, RFC 2119, March 1997. 905 [RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol 906 (MOBIKE)", RFC 4555, June 2006. 908 [RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, 909 "Internet Key Exchange Protocol: IKEv2", RFC 5996, 910 September 2010. 912 13.2. Informative References 914 [RFC5723] Sheffer, Y. and H. Tschofenig, "IKEv2 Session Resumption", 915 RFC 5723, January 2010. 917 [cluster] Nir, Y., Ed., "IPsec Cluster Problem Statement", 918 draft-ietf-ipsecme-ipsec-ha (work in progress), July 2010. 920 [recovery] 921 Detienne, F., Sethi, P., and Y. Nir, "Safe IKE Recovery", 922 draft-detienne-ikev2-recovery (work in progress), 923 January 2010. 925 Appendix A. The Path Not Taken 927 A.1. Initiating a new IKE SA 929 Instead of sending a QCD token, we could have the rebooted 930 implementation start an Initial exchange with the peer, including the 931 INITIAL_CONTACT notification. This would have the same effect, 932 instructing the peer to erase the old IKE SA, as well as establishing 933 a new IKE SA with fewer rounds. 935 The disadvantage here, is that in IKEv2 an authentication exchange 936 MUST have a piggy-backed Child SA set up. Since our use case is such 937 that the rebooted implementation does not have traffic flowing to the 938 peer, there are no good selectors for such a Child SA. 940 Additionally, when authentication is asymmetric, such as when EAP is 941 used, it is not possible for the rebooted implementation to initiate 942 IKE. 944 A.2. SIR 946 Another proposal that was considered for this work item is the SIR 947 extension, which is described in [recovery]. Under that proposal, 948 the non-rebooted peer sends a non-protected query to the possibly 949 rebooted peer, asking whether the IKE SA exists. The peer replies 950 with either a positive or negative response, and the absence of a 951 positive response, along with the existence of a negative response is 952 taken as proof that the IKE SA has really been lost. 954 The working group preferred the QCD proposal to this one. 956 A.3. Birth Certificates 958 Birth Certificates is a method of crash detection that has never been 959 formally defined. Bill Sommerfeld suggested this idea in a mail to 960 the IPsec mailing list on August 7, 2000, in a thread discussing 961 methods of crash detection: 963 If we have the system sign a "birth certificate" when it 964 reboots (including a reboot time or boot sequence number), 965 we could include that with a "bad spi" ICMP error and in 966 the negotiation of the IKE SA. 968 We believe that this method would have some problems. First, it 969 requires Alice to store the certificate, so as to be able to compare 970 the public keys. That requires more storage than does a QCD token. 971 Additionally, the public-key operations needed to verify the self- 972 signed certificates are more expensive for Alice. 974 We believe that a symmetric-key operation such as proposed here is 975 more light-weight and simple than that implied by the Birth 976 Certificate idea. 978 A.4. Reducing Liveness Check Length 980 Some implementations require fewer retransmissions over a shorter 981 period of time for cases of liveness check started because of an 982 INVALID_SPI or INVALID_IKE_SPI notification. 984 We believe that the default retransmission policy should represent a 985 good balance between the need for a timely discovery of a dead peer, 986 and a low probability of false detection. We expect the policy to be 987 set to take the shortest time such that this probability achieves a 988 certain target. Therefore, we believe that reducing the elapsed time 989 and retransmission count may create an unacceptably high probability 990 of false detection, and this can be triggered by a single 991 INVALID_IKE_SPI notification. 993 Additionally, even if the retransmission policy is reduced to, say, 994 one minute, it is still a very noticeable delay from a human 995 perspective, from the time that the gateway has come up (i.e., is 996 able to respond with an INVALID_SPI or INVALID_IKE_SPI notification) 997 and until the tunnels are active, or from the time the backup gateway 998 has taken over until the tunnels are active. The use of QCD tokens 999 can reduce this delay. 1001 Authors' Addresses 1003 Yoav Nir (editor) 1004 Check Point Software Technologies Ltd. 1005 5 Hasolelim st. 1006 Tel Aviv 67897 1007 Israel 1009 Email: ynir@checkpoint.com 1011 David Wierbowski 1012 International Business Machines 1013 1701 North Street 1014 Endicott, New York 13760 1015 United States 1017 Email: wierbows@us.ibm.com 1019 Frederic Detienne 1020 Cisco Systems, Inc. 1021 De Kleetlaan, 7 1022 Diegem B-1831 1023 Belgium 1025 Phone: +32 2 704 5681 1026 Email: fd@cisco.com 1028 Pratima Sethi 1029 Cisco Systems, Inc. 1030 O'Shaugnessy Road, 11 1031 Bangalore, Karnataka 560027 1032 India 1034 Phone: +91 80 4154 1654 1035 Email: psethi@cisco.com