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Weniger 5 Expires: August 13, 2009 February 9, 2009 7 Re-direct Mechanism for IKEv2 8 draft-ietf-ipsecme-ikev2-redirect-04.txt 10 Status of this Memo 12 This Internet-Draft is submitted to IETF in full conformance with the 13 provisions of BCP 78 and BCP 79. 15 Internet-Drafts are working documents of the Internet Engineering 16 Task Force (IETF), its areas, and its working groups. Note that 17 other groups may also distribute working documents as Internet- 18 Drafts. 20 Internet-Drafts are draft documents valid for a maximum of six months 21 and may be updated, replaced, or obsoleted by other documents at any 22 time. 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Please review these documents 42 carefully, as they describe your rights and restrictions with respect 43 to this document. 45 Abstract 47 IKEv2 is a protocol for setting up VPN tunnels from a remote location 48 to a gateway so that the VPN client can access services in the 49 network behind the gateway. Currently there is no standard mechanism 50 specified that allows an overloaded VPN gateway or a VPN gateway that 51 is being shut down for maintenance to re-direct the VPN client to 52 attach to another gateway. This document proposes a re-direct 53 mechanism for IKEv2. The proposed mechanism can also be used in 54 Mobile IPv6 to enable the home agent to re-direct the mobile node to 55 another home agent. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 60 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 61 3. IKEv2 Exchange with Redirect . . . . . . . . . . . . . . . . . 4 62 4. Use of Anycast Addresses with the Re-direct Mechanism . . . . 5 63 5. Gateway Initiated Redirect . . . . . . . . . . . . . . . . . . 6 64 6. Redirect Messages . . . . . . . . . . . . . . . . . . . . . . 7 65 6.1. REDIRECT_SUPPORTED . . . . . . . . . . . . . . . . . . . . 7 66 6.2. REDIRECT . . . . . . . . . . . . . . . . . . . . . . . . . 8 67 6.3. REDIRECTED_FROM . . . . . . . . . . . . . . . . . . . . . 9 68 7. Use of the Redirect Mechanism between IKEv2 Peers . . . . . . 10 69 8. Security Considerations . . . . . . . . . . . . . . . . . . . 10 70 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 71 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 72 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 73 11.1. Normative References . . . . . . . . . . . . . . . . . . . 11 74 11.2. Informative References . . . . . . . . . . . . . . . . . . 11 75 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 77 1. Introduction 79 IKEv2 [2] is used for setting up IPsec-based VPNs. The IP address of 80 the VPN gateway can be configured on the VPN client. But this does 81 not scale well, when the number of VPN gateways is large. Dynamic 82 discovery of VPN gateways using DNS is quite widely used too. 83 However, using DNS is not flexible when it comes to assigning a VPN 84 gateway to the VPN client based on the load on the VPN gateways. The 85 VPN client typically tries to connect to the IP address of the VPN 86 gateways that appears first in the DNS response. If the VPN tunnel 87 setup fails, then the VPN client tries to attach to the other VPN 88 gateways returned in the DNS response. 90 This document proposes a re-direct mechanism for IKEv2 that enables a 91 VPN gateway to re-direct the VPN client to another VPN gateway, for 92 example, based on the load condition. The re-direct can be done 93 during during the IKE_SA_INIT or the IKE_AUTH exchange. Gateway- 94 initiated re-direct in the middle of a session is also supported. 95 The re-direct mechanism can also be used in conjunction with anycast 96 addresses. In this case, anycast address for the cluster of VPN 97 gateways is stored in the DNS instead of a list of unicast IP 98 addresses of the VPN gateways. 100 The re-direct can also happen because of administrative or optimal 101 routing reasons. This document does not attempt to provide an 102 exhaustive list of reasons for re-directing a VPN client to another 103 VPN gateway. 105 Mobile IPv6 [3] may use IKEv2 for mutual authentication between the 106 mobile node and the home agent. IKEv2 may also be used for home 107 address configuration and setting up IPsec security associations for 108 protecting Mobile IPv6 signaling messages [4]. The IKEv2 exchange 109 precedes the exchange of Mobile IPv6 signaling messages. Therefore 110 the mechanism described in this document can be also be used by a 111 Mobile IPv6 home agent to re-direct a mobile node to another home 112 agent. 114 There is a Home Agent Switch mechanism available for re-directing a 115 mobile node to another home agent, described in [5]. The Home Agent 116 Switch mechanism can only be used after the binding cache had been 117 created at the home agent for the mobile node. The disadvantage with 118 this is that quite a bit of state is created on the home agent before 119 the mobile node can be re-directed to another home agent. The 120 mechanism described in this document can be used for re-directing a 121 mobile node before any state related to the Mobile IPv6 binding is 122 created on the home agent. 124 2. Terminology 126 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 127 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 128 document are to be interpreted as described in [1]. 130 3. IKEv2 Exchange with Redirect 132 To redirect an IKEv2 session to another VPN gateway, the VPN gateway 133 that initially received the IKE_SA_INIT request selects another VPN 134 gateway and responds to the VPN client with a REDIRECT Notification 135 payload. The mechanism by which the initial VPN gateway selects 136 another VPN gateway is out of scope for this document. The IP 137 address of the selected VPN gateway is sent in the REDIRECT payload. 139 The VPN client indicates support for the IKEv2 redirect mechanism by 140 including a REDIRECT_SUPPORTED notification message in the initial 141 IKE_SA_INIT request. If the IKE_SA_INIT request did not include the 142 REDIRECT_SUPPORTED payload, the responder MUST NOT send the REDIRECT 143 payload to the VPN client. 145 Initiator Responder (initial VPN GW) 146 --------- ------------------------- 148 (IP_I:500 -> Initial_IP_R:500) 149 HDR(A,0), SAi1, KEi, Ni, --> 150 N(REDIRECT_SUPPORTED) 152 (Initial_IP_R:500 -> IP_I:500) 153 <-- HDR(A,0), N(REDIRECT, IP_R) 155 When the VPN client receives the IKE_SA_INIT response with the 156 REDIRECT payload, it initiates a new IKE_SA_INIT exchange with the 157 VPN gateway listed in the REDIRECT payload. The VPN client includes 158 the IP address of the original VPN gateway that re-directed the 159 client. The IKEv2 exchange then proceeds as normal with the selected 160 VPN gateway. 162 Initiator Responder (Selected VPN GW) 163 --------- --------------------------- 165 (IP_I:500 -> IP_R:500) 166 HDR(A,0), SAi1, KEi, Ni, --> 167 N(REDIRECTED_FROM, Initial_IP_R) 169 (IP_R:500 -> IP_I:500) 170 <-- HDR(A,B), SAr1, KEr, Nr,[CERTREQ] 172 (IP_I:500 -> IP_R:500) 173 HDR(A,B), SK {IDi, [CERT,] [CERTREQ,] 174 [IDr,]AUTH, SAi2, TSi, TSr} --> 176 (IP_R:500 -> IP_I:500) 177 <-- HDR(A,B), SK {IDr, [CERT,] AUTH, 178 SAr2, TSi, TSr} 180 When this mechanism is used with Mobile IPv6, a mobile node's 181 security associations with its home agent may expire while it still 182 has a valid binding cache entry at the home agent. In this case, the 183 mobile node MUST NOT use the original home agent address as the 184 destination address in the IKE_SA_INIT exchange to setup new security 185 associations. It MUST try to setup security associations with its 186 existing home agent. 188 4. Use of Anycast Addresses with the Re-direct Mechanism 190 The use of anycast addresses will avoid having to configure a 191 particular VPN gateway's IP address in the DNS. Instead, the anycast 192 address that represents the group of VPN gateways is stored in the 193 DNS. When the VPN client performs a DNS lookup for the VPN gateway, 194 it receives the anycast address of the VPN gateway in the DNS 195 response. 197 If an anycast address is returned in response to DNS resolution of an 198 FQDN, the IKEv2 transaction between the VPN client and the VPN 199 gateway is slightly modified. The VPN client sends the IKE_SA_INIT 200 request to the anycast address. The IKE_SA_INIT request is routed to 201 one of the VPN gateways that is part of the anycast group. The VPN 202 gateway that receives the IKE_SA_INIT request responds with an 203 IKE_SA_INIT reply from the anycast address. 205 Initiator Responder (any VPN GW) 206 --------- ------------------------- 208 (IP_I:500 -> ANYCAST:500) 209 HDR(A,0), SAi1, KEi, Ni) --> 210 N(REDIRECT_SUPPORTED) 212 (ANYCAST:500 -> IP_I:500) 213 <-- HDR(A,0), N(REDIRECT, IP_R) 215 If the destination address on the IKE_SA_INIT request is an anycast 216 address, the VPN gateway that received the IKE_SA_INIT request MUST 217 include the REDIRECT payload to re-direct the VPN client to a unicast 218 address of one of the VPN gateway. The VPN gateway that received the 219 IKE_SA_INIT request MAY re-direct the client to its own unicast 220 address, if it is not overloaded. 222 The rest of the IKEv2 exchange is the same as described in Section 3. 224 5. Gateway Initiated Redirect 226 The re-direct mechanism may also be used by a VPN gateway to re- 227 direct the client to another VPN gateway in middle of a session. To 228 re-direct a client, the gateway should send an INFORMATIONAL message 229 with the REDIRECT Notify payload. The REDIRECT payload MUST carry 230 information about the new VPN gateway. When the client receives this 231 message, it MUST send an empty message as an acknowledgement. Until 232 the client responds with an acknowledgement, the gateway SHOULD re- 233 transmit the re-direct INFORMATIONAL message as described in [2]. 234 The following illustrates the INFORMATIONAL message exchange for 235 gateway-initiated redirect. 237 Initiator (VPN client) Responder (VPN GW) 238 ---------------------- ------------------ 240 <-- HDR, SK {N[REDIRECT, IP_R/FQDN_R]} 242 HDR, SK {} --> 244 The INFORMATIONAL message exchange described above is protected by 245 the existing IKEv2 SA between the client and the gateway. 247 Once the client sends an acknowledgement to the gateway, it SHOULD 248 delete the existing security associations with the old gateway by 249 sending an Informational message with a DELETE payload. The gateway 250 MAY also decide to delete the security associations without any 251 signaling from the client. However, it should allow sufficient time 252 for the client to setup the required security associations with the 253 new security gateway. This time period should be configurable on the 254 gateway. 256 If the gateway decides to re-direct the client during the IKE_AUTH 257 exchange, it prevents the creation of a CHILD SA by sending the 258 NO_ADDITIONAL_SAS Notify Payload in the IKE_AUTH response. It then 259 follows up with an INFORMATIONAL message with the REDIRECT payload 260 immediately. The following shows the message exchange between the 261 client and the gateway. 263 Initiator Responder ( VPN GW) 264 --------- ------------------- 266 (IP_I:500 -> IP_R:500) 267 HDR(A,0), SAi1, KEi, Ni, --> 268 N(REDIRECTED_SUPPORTED) 270 (IP_R:500 -> IP_I:500) 271 <-- HDR(A,B), SAr1, KEr, Nr,[CERTREQ] 273 (IP_I:500 -> IP_R:500) 274 HDR(A,B), SK {IDi, [CERT,] [CERTREQ,] 275 [IDr,]AUTH, SAi2, TSi, TSr} --> 277 (IP_R:500 -> IP_I:500) 278 <-- HDR(A,B), SK {IDr, [CERT,] AUTH, 279 N(NO_ADDITIONAL_SAS)} 281 <-- HDR, SK {N[REDIRECT, IP_R/FQDN_R]} 283 HDR, SK {} --> 285 When the client receives the IKE_AUTH response with the 286 NO_ADDITIONAL_SAS payload from the gateway, it may decide to delete 287 the IKEv2 SA. In case the gateway receives the INFORMATIONAL message 288 to delete the IKEv2 SA before sending the REDIRECT message, then the 289 gateway includes the REDIRECT payload in the response along with the 290 DELETE payload. 292 6. Redirect Messages 294 6.1. REDIRECT_SUPPORTED 296 The REDIRECT_SUPPORTED payload is included in the initial IKE_SA_INIT 297 request by the initiator to indicate support for the IKEv2 re-direct 298 mechanism described in this document. 300 1 2 3 301 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 1 302 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 303 | Next Payload |C| RESERVED | Payload Length | 304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 305 | Protocol ID | SPI Size (=0) | Notify Message Type | 306 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 308 The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size' and 309 the 'Notify Message Type' fields are the same as described in Section 310 3.10 of [2]. The 'SPI Size' field MUST be set to 0 to indicate that 311 the SPI is not present in this message. 313 The 'Payload Length' field MUST be set to '8'. The 'Notify Message 314 Type' field is set to indicate the REDIRECT_SUPPORTED payload . 317 6.2. REDIRECT 319 The REDIRECT payload is included in an IKE_SA_INIT response from the 320 responder when the responder wants to re-direct the initiator to 321 another VPN gateway. The message includes the new responder's IP 322 address. 324 1 2 3 325 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 1 326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 327 | Next Payload |C| RESERVED | Payload Length | 328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 329 | Protocol ID | SPI Size (=0) | Notify Message Type | 330 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 331 | GW Ident Type | | 332 +---------------+ ~ 333 ~ New Responder GW Identity ~ 334 | | 335 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 337 The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size' and 338 the 'Notify Message Type' fields are the same as described in Section 339 3.10 of [2]. The 'SPI Size' field MUST be set to 0 to indicate that 340 the SPI is not present in this message. 342 If the IP address of the new VPN gateway is sent, the 'Payload 343 Length' field MUST be set to either '13' or '25' depending on whether 344 an IPv4 or IPv6 address is sent in the message. If the FQDN of the 345 new VPN gateway is sent, the 'Payload Length' field is set to the 346 length of the FQDN plus the fixed fields in the message. The 'Notify 347 Message Type' field is set to indicate the REDIRECT payload . The 'GW Identity Type' field indicates the 349 type of information that is sent to identify the new VPN gateway. 350 The following values are reserved by this document. 352 1 - IPv4 address of the new VPN gateway 353 2 - IPv6 address of the new VPN gateway 354 3 - FQDN of the new VPN gateway 356 All other values for this field are reserved and MUST NOT be used. 357 The identity of the new VPN gateway is carried in the 'New Responder 358 GW Identity' field. 360 6.3. REDIRECTED_FROM 362 The REDIRECTED_FROM message type is included in the IKE_SA_INIT 363 request from the initiator to the new VPN gateway to indicate the IP 364 address of the original VPN gateway that re-directed the initiator. 365 The original VPN gateway's IP address is included in the message. 367 1 2 3 368 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 1 369 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 370 | Next Payload |C| RESERVED | Payload Length | 371 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 372 | Protocol ID | SPI Size (=0) | Notify Message Type | 373 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 374 | GW Ident Type | | 375 +---------------+ ~ 376 ~ Original Responder GW Identity ~ 377 | | 378 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 380 The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size' and 381 the 'Notify Message Type' fields are the same as described in Section 382 3.10 of [2] The 'SPI Size' field MUST be set to 0 to indicate that 383 the SPI is not present in this message. 385 The 'Payload Length' field MUST be set to either '13' or '25' 386 depending on whether an IPv4 or IPv6 address of the original VPN 387 gateway is sent in the message. The 'Notify Message Type' field is 388 set to indicate the REDIRECTED_FROM payload . The 'GW Identity Type' field indicates the type of 390 information that is sent to identify the new VPN gateway. The 391 following values are reserved by this document. 393 1 - IPv4 address of the original VPN gateway 394 2 - IPv6 address of the original VPN gateway 396 All other values for this field are reserved and MUST NOT be used. 397 The identity of the original VPN gateway is carried in the 'Original 398 Responder GW Identity' field. 400 7. Use of the Redirect Mechanism between IKEv2 Peers 402 The Re-direct mechanism described in this document is mainly intended 403 for use in client-gateway scenarios. However, the mechanism can also 404 be used between any two IKEv2 peers. This is especially useful for 405 IKEv2 sessions between two gateway peer routers. 407 When used between a client and gateway, the re-direct procedure is 408 always initiated by the gateway. But when used between two IKEv2 409 peers, either of the IKEv2 end points can initiate the re-direct 410 message. In order to prevent any race condition that might occur if 411 both decide to re-direct at the same time, the responder MUST NOT 412 respond to re-direct message from the initiator, if it has already 413 decided to re-direct the initiator. 415 Both IKEv2 peers SHOULD indicate support for the re-direct mechanism 416 if they support it and are willing to process REDIRECT notification 417 messages. This is done by including the REDIRECT_SUPPORTED payload 418 in the IKE_SA_INIT exchange by both peers. REDIRECT Notification 419 messages MUST NOT be sent unless the peer has indicated support for 420 it. 422 8. Security Considerations 424 An eavesdropper on the path between VPN client and server may send a 425 redirect to the client upon receiving an IKE_SA_INIT message from 426 this client. This is no problem regarding DoS attacks for the VPN 427 connection, since an on-path-attacker can as well drop the 428 IKE_SA_INIT requests to prevent VPN access for the client. But an 429 eavesdropper on the path between VPN client and server can redirect a 430 large number of clients to a victim, which is then flooded with 431 IKE_SA_INIT requests. Flooding only happens if many clients initiate 432 IKEv2 exchange at almost the same time, which is considered a rare 433 event. However, this may happen if a Home Agent/VPN server is 434 shutdown for maintenance and all clients need to re-establish VPN 435 connections with another Home Agent/VPN server or if the on-path 436 attacker forces all IPsec security associations to expire by dropping 437 all received IKEv2 messages. 439 The use of REDIRECTED_FROM payload is intended to discourage a rogue 440 VPN gateway from re-directing a large number of VPN clients to a 441 particular VPN gateway. It does not prevent such a DoS attack. 443 9. IANA Considerations 445 This document defines four new IKEv2 Notification Message types as 446 described in Section 6. The three Notify Message Types must be 447 assigned values between 16396 and 40959. 449 o REDIRECT_SUPPORTED 450 o REDIRECT 451 o REDIRECTED_FROM 453 10. Acknowledgements 455 The use of anycast address with IKEv2 was first described in [6]. It 456 was then added to an early draft version of RFC 5026 and later 457 removed before the RFC was published. Therefore the authors of [6] 458 and RFC 5026 are acknowledged. 460 Thanks to Pasi Eronen, with whom the solution described in this 461 document was extensively discussed. Thanks to Tero Kivinen for 462 suggesting the use of REDIRECTED_FROM payload. The authors would 463 also like to thank Yaron Sheffer, Sunil Kumar, Fan Zhao, Yoav Nir and 464 Arnaud Ebalard for their reviews and comments. 466 11. References 468 11.1. Normative References 470 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 471 Levels", BCP 14, RFC 2119, March 1997. 473 [2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC 4306, 474 December 2005. 476 11.2. Informative References 478 [3] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in 479 IPv6", RFC 3775, June 2004. 481 [4] Giaretta, G., Kempf, J., and V. Devarapalli, "Mobile IPv6 482 Bootstrapping in Split Scenario", RFC 5026, October 2007. 484 [5] Haley, B., Devarapalli, V., Deng, H., and J. Kempf, "Mobility 485 Header Home Agent Switch Message", RFC 5142, January 2008. 487 [6] Weniger, K. and F. Dupont, "IKEv2-based Home Agent Assignment in 488 Mobile IPv6/NEMO Bootstrapping", draft-dupont-ikev2-haassign-02 489 (work in progress), January 2007. 491 Authors' Addresses 493 Vijay Devarapalli 494 WiChorus 495 3590 North First St 496 San Jose, CA 95134 497 USA 499 Email: vijay@wichorus.com 501 Kilian Weniger 503 Email: kilian.weniger@googlemail.com