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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) ** Obsolete normative reference: RFC 4306 (ref. '2') (Obsoleted by RFC 5996) -- Obsolete informational reference (is this intentional?): RFC 3775 (ref. '3') (Obsoleted by RFC 6275) Summary: 2 errors (**), 0 flaws (~~), 2 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group V. Devarapalli 3 Internet-Draft WiChorus 4 Intended status: Standards Track K. Weniger 5 Expires: November 20, 2009 May 19, 2009 7 Redirect Mechanism for IKEv2 8 draft-ietf-ipsecme-ikev2-redirect-10.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. This document may not be modified, 14 and derivative works of it may not be created, except to format it 15 for publication as an RFC or to translate it into languages other 16 than English. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on November 20, 2009. 36 Copyright Notice 38 Copyright (c) 2009 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents in effect on the date of 43 publication of this document (http://trustee.ietf.org/license-info). 44 Please review these documents carefully, as they describe your rights 45 and restrictions with respect to this document. 47 Abstract 49 IKEv2 is a protocol for setting up VPN tunnels from a remote location 50 to a gateway so that the VPN client can access services in the 51 network behind the gateway. Currently there is no standard mechanism 52 specified that allows an overloaded VPN gateway or a VPN gateway that 53 is being shut down for maintenance to redirect the VPN client to 54 attach to another gateway. This document proposes a redirect 55 mechanism for IKEv2. The proposed mechanism can also be used in 56 Mobile IPv6 to enable the home agent to redirect the mobile node to 57 another home agent. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 62 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 63 3. IKEv2 Initial Exchange with Redirect . . . . . . . . . . . . . 4 64 4. Use of Anycast Addresses with the Redirect Mechanism . . . . . 6 65 5. Gateway Initiated Redirect . . . . . . . . . . . . . . . . . . 7 66 6. Redirect During IKE_AUTH Exchange . . . . . . . . . . . . . . 7 67 7. Redirect Messages . . . . . . . . . . . . . . . . . . . . . . 8 68 7.1. REDIRECT_SUPPORTED . . . . . . . . . . . . . . . . . . . . 8 69 7.2. REDIRECT . . . . . . . . . . . . . . . . . . . . . . . . . 9 70 7.3. REDIRECTED_FROM . . . . . . . . . . . . . . . . . . . . . 10 71 8. Use of the Redirect Mechanism between IKEv2 Peers . . . . . . 11 72 9. Security Considerations . . . . . . . . . . . . . . . . . . . 11 73 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 74 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 75 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 76 12.1. Normative References . . . . . . . . . . . . . . . . . . . 13 77 12.2. Informative References . . . . . . . . . . . . . . . . . . 13 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 80 1. Introduction 82 IKEv2 [2] is used for setting up IPsec-based VPNs. The IP address of 83 the VPN gateway can be configured on the VPN client. But this does 84 not scale well, when the number of VPN gateways is large. Dynamic 85 discovery of VPN gateways using DNS is quite widely used too. 86 However, using DNS is not flexible when it comes to assigning a VPN 87 gateway to the VPN client based on the load on the VPN gateways. The 88 VPN client typically tries to connect to the IP address of the VPN 89 gateway that appears first in the DNS response. If the VPN tunnel 90 setup fails, then the VPN client tries to attach to the other VPN 91 gateways returned in the DNS response. 93 This document proposes a redirect mechanism for IKEv2 that enables a 94 VPN gateway to redirect the VPN client to another VPN gateway, for 95 example, based on the load condition. The redirect can be done 96 during the IKE_SA_INIT or the IKE_AUTH exchange. Gateway-initiated 97 redirect in the middle of a session is also supported. The redirect 98 mechanism can also be used in conjunction with anycast addresses. In 99 this case, anycast address for the cluster of VPN gateways is stored 100 in the DNS instead of a list of unicast IP addresses of the VPN 101 gateways. 103 The redirect can also happen because of administrative or optimal 104 routing reasons. This document does not attempt to provide an 105 exhaustive list of reasons for redirecting a VPN client to another 106 VPN gateway. 108 Mobile IPv6 [3] may use IKEv2 for mutual authentication between the 109 mobile node and the home agent. IKEv2 may also be used for home 110 address configuration and setting up IPsec security associations for 111 protecting Mobile IPv6 signaling messages [4]. The IKEv2 exchange 112 precedes the exchange of Mobile IPv6 signaling messages. Therefore 113 the mechanism described in this document can also be used by a Mobile 114 IPv6 home agent to redirect a mobile node to another home agent. 116 There is a Home Agent Switch mechanism available for redirecting a 117 mobile node to another home agent, described in [5]. The Home Agent 118 Switch mechanism can only be used after the binding cache had been 119 created at the home agent for the mobile node. The disadvantage with 120 this is that quite a bit of state is created on the home agent before 121 the mobile node can be redirected to another home agent. The 122 mechanism described in this document can be used for redirecting a 123 mobile node before any state related to the Mobile IPv6 binding is 124 created on the home agent. 126 2. Terminology 128 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 129 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 130 document are to be interpreted as described in [1]. 132 3. IKEv2 Initial Exchange with Redirect 134 This section describes the use of Redirect mechanism during the 135 IKE_SA_INIT exchange. Gateway-initiated redirect and the use of 136 redirect during IKE_AUTH exchange are explained in subsequent 137 sections. 139 The VPN client indicates support for the IKEv2 redirect mechanism and 140 the willingness to be redirected by including a REDIRECT_SUPPORTED 141 notification message in the initial IKE_SA_INIT request. If the 142 IKE_SA_INIT request did not include the REDIRECT_SUPPORTED payload, 143 the responder MUST NOT send the REDIRECT payload to the VPN client. 145 To redirect an IKEv2 session to another VPN gateway, the VPN gateway 146 that initially received the IKE_SA_INIT request selects another VPN 147 gateway (how the selection is made is beyond the scope of this 148 document), and replies with an IKE_SA_INIT response containing a 149 REDIRECT notification message. The notification includes information 150 about the selected VPN gateway, and the nonce data from the Ni 151 payload in the IKE_SA_INIT request. 153 Note that when the IKE_SA_INIT response includes the REDIRECT 154 notification, the exchange does not result in the creation of an 155 IKE_SA and the responder SPI will be zero. 157 Initiator Responder (initial VPN GW) 158 --------- ------------------------- 160 (IP_I:500 -> Initial_IP_R:500) 161 HDR(A,0), SAi1, KEi, Ni, --> 162 N(REDIRECT_SUPPORTED) 164 (Initial_IP_R:500 -> IP_I:500) 165 <-- HDR(A,0), N(REDIRECT, New_GW_ID, Ni_data) 167 When the client receives the IKE_SA_INIT response, it MUST verify 168 that the nonce data matches the value sent in the IKE_SA_INIT 169 request. If the values do not match, the client MUST silently 170 discard the response (and keep waiting for another response). This 171 prevents certain Denial-of-Service attacks on the initiator that 172 could be caused by an attacker injecting IKE_SA_INIT responses with 173 the REDIRECT payloads. 175 Next, the client initiates a new IKE_SA_INIT exchange with the VPN 176 gateway listed in the REDIRECT payload provided this is allowed by 177 its IPsec policy. The VPN client includes the IP address of the 178 original VPN gateway that redirected the client in the 179 REDIRECTED_FROM notification. The IKEv2 exchange then proceeds as it 180 would have proceeded with the original VPN gateway. 182 Initiator Responder (Selected VPN GW) 183 --------- --------------------------- 185 (IP_I:500 -> IP_R:500) 186 HDR(A,0), SAi1, KEi, Ni, --> 187 N(REDIRECTED_FROM, Initial_IP_R) 189 (IP_R:500 -> IP_I:500) 190 <-- HDR(A,B), SAr1, KEr, Nr,[CERTREQ] 192 (IP_I:500 -> IP_R:500) 193 HDR(A,B), SK {IDi, [CERT,] [CERTREQ,] 194 [IDr,]AUTH, SAi2, TSi, TSr} --> 196 (IP_R:500 -> IP_I:500) 197 <-- HDR(A,B), SK {IDr, [CERT,] AUTH, 198 SAr2, TSi, TSr} 200 In particular, the client MUST use the same Peer Authorization 201 Database (PAD) and Security Policy Database (SPD) entries as it would 202 have used with the original gateway. Receiving a redirect 203 notification MUST NOT result in the modification of any PAD or SPD 204 entries. In practice, this means the new gateway either has to use 205 the same responder identity (IDr) as the original gateway, or both 206 should be part of a group of responders that are authorized by the 207 same PAD entry. See section 4.4.3.1 of [8] on using DNS names to 208 represent a group of peers in a PAD entry. 210 When running IKEv2 between a Mobile IPv6 Mobile Node (MN) and Home 211 Agent (HA), redirecting the IKEv2 exchange to another HA is not 212 enough; the Mobile IPv6 signalling also needs to be sent to the new 213 HA address. The MN MAY treat the information received in the 214 IKE_SA_INIT response in similar way as it would treat HA discovery 215 information received from other unauthenticated (and potentially 216 untrustworthy) sources (such as DNS lookups not protected with 217 DNSSEC). However, if the MN has authenticated information about its 218 Home Agent, it MUST NOT be updated based on the IKE_SA_INIT response. 220 If the REDIRECT notification is received during the IKE_AUTH exchange 221 (after the HA has been authenticated; see Section 6), the MN MAY pass 222 the new address to Mobile IPv6 and treat it in similar fashion as 223 information from the Home Agent Switch Message [5]. 225 Gateway-initiated REDIRECT notifications exchanged in INFORMATIONAL 226 exchanges (see Section 5) MUST NOT result in updating any Mobile IPv6 227 state. In such cases, the Home Agent Switch Message specified in [5] 228 is used instead. 230 4. Use of Anycast Addresses with the Redirect Mechanism 232 The use of anycast addresses will avoid having to configure a 233 particular VPN gateway's IP address in the DNS. Instead, the anycast 234 address that represents the group of VPN gateways is stored in the 235 DNS. When the VPN client performs a DNS lookup for the VPN gateway, 236 it receives the anycast address of the VPN gateway in the DNS 237 response. 239 If an anycast address is returned in response to DNS resolution of an 240 FQDN, the VPN client sends the IKE_SA_INIT request to the anycast 241 address. The IKE_SA_INIT request is routed to one of the VPN 242 gateways that is part of the anycast group. The VPN gateway that 243 receives the IKE_SA_INIT request responds with an IKE_SA_INIT reply 244 from the anycast address. 246 Initiator Responder (any VPN GW) 247 --------- ------------------------- 249 (IP_I:500 -> ANYCAST:500) 250 HDR(A,0), SAi1, KEi, Ni) --> 251 N(REDIRECT_SUPPORTED) 253 (ANYCAST:500 -> IP_I:500) 254 <-- HDR(A,0), N(REDIRECT, New_GW_ID, Ni_data) 256 If the destination address on the IKE_SA_INIT request is an anycast 257 address, the VPN gateway that received the IKE_SA_INIT request MUST 258 include the REDIRECT payload to redirect the VPN client to a unicast 259 address of one of the VPN gateway. The VPN gateway that received the 260 IKE_SA_INIT request MAY redirect the client to its own unicast 261 address, if it is not overloaded. 263 The rest of the IKEv2 exchange is the same as described in Section 3. 265 5. Gateway Initiated Redirect 267 The redirect mechanism may also be used by a VPN gateway to redirect 268 the client to another VPN gateway in middle of a session. To 269 redirect a client, the gateway should send an INFORMATIONAL message 270 with the REDIRECT Notify payload. The REDIRECT payload MUST carry 271 information about the new VPN gateway. The gateway MUST NOT include 272 any nonce data in the REDIRECT payload, since it is a gateway- 273 initiated message and is protected by the IKEv2 security association. 274 When the client receives this message, it MUST send an empty message 275 as an acknowledgement. Until the client responds with an 276 acknowledgement, the gateway SHOULD re-transmit the redirect 277 INFORMATIONAL message as described in [2]. The following illustrates 278 the INFORMATIONAL message exchange for gateway-initiated redirect. 280 Initiator (VPN client) Responder (VPN GW) 281 ---------------------- ------------------ 283 <-- HDR, SK {N(REDIRECT, New_GW_ID)} 285 HDR, SK {} --> 287 The INFORMATIONAL message exchange described above is protected by 288 the existing IKEv2 SA between the client and the gateway. 290 Once the client sends an acknowledgement to the gateway, it SHOULD 291 delete the existing security associations with the old gateway by 292 sending an Informational message with a DELETE payload. The gateway 293 MAY also decide to delete the security associations without any 294 signaling from the client, again by sending an Informational message 295 with a DELETE payload. However, it should allow sufficient time for 296 the client to setup the required security associations with the new 297 security gateway. This time period should be configurable on the 298 gateway. 300 6. Redirect During IKE_AUTH Exchange 302 If the gateway decides to redirect the client during the IKE_AUTH 303 exchange, based on the identity presented by the client in the 304 IKE_AUTH request message, it prevents the creation of a CHILD SA and 305 sends the REDIRECT payload in the IKE_AUTH response. When the client 306 receives the IKE_AUTH response with the REDIRECT payload, it SHOULD 307 delete the existing IKEv2 security association with the gateway by 308 sending an Informational message with a DELETE payload. The gateway 309 MUST verify the client's AUTH payload before sending the Redirect 310 payload, and the client MUST verify the gateway's AUTH payload before 311 acting on the Redirect payload. 313 Initiator Responder ( VPN GW) 314 --------- ------------------- 316 (IP_I:500 -> IP_R:500) 317 HDR(A,0), SAi1, KEi, Ni, --> 318 N(REDIRECTED_SUPPORTED) 320 (IP_R:500 -> IP_I:500) 321 <-- HDR(A,B), SAr1, KEr, Nr,[CERTREQ] 323 (IP_I:500 -> IP_R:500) 324 HDR(A,B), SK {IDi, [CERT,] [CERTREQ,] 325 [IDr,]AUTH, SAi2, TSi, TSr} --> 327 (IP_R:500 -> IP_I:500) 328 <-- HDR(A,B), SK {IDr, [CERT,] AUTH, 329 N(REDIRECT, New_GW_ID)} 331 In case the IKE_AUTH exchange involves EAP authentication as 332 described in Section 2.16 of RFC 4306 [2], or multiple authentication 333 methods as described in RFC 4739 [6], the gateway may decide to 334 redirect the client based on the interaction with the AAA server or 335 the external authentication server. In this case, the gateway MUST 336 send the REDIRECT Notification payload in either the first or the 337 last IKE_AUTH response. The client and the gateway MUST verify the 338 AUTH payloads as described above. 340 When EAP is used, the gateway MAY also redirect the client based on 341 the unauthenticated identity presented by the client in the first 342 IKE_AUTH exchange itself. Since EAP is used as the authentication 343 mechanism, the client does not include AUTH payload to authenticate 344 his identity, but the server still MUST include his own AUTH payload, 345 and client MUST verify it. Note that the IKEv2 SA is not created in 346 this case and the client does not have to explicitly delete the IKEv2 347 SA. 349 In all of the cases above, the client MUST accept the REDIRECT 350 notification only in the first IKE_AUTH response or the last IKE_AUTH 351 response. It MUST NOT accept the REDIRECT notification in an 352 intermediate IKE_AUTH response. 354 7. Redirect Messages 356 7.1. REDIRECT_SUPPORTED 358 The REDIRECT_SUPPORTED payload is included in the initial IKE_SA_INIT 359 request by the initiator to indicate support for the IKEv2 redirect 360 mechanism described in this document. 362 1 2 3 363 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 1 364 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 365 | Next Payload |C| RESERVED | Payload Length | 366 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 367 | Protocol ID | SPI Size (=0) | Notify Message Type | 368 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 370 The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size' and 371 the 'Notify Message Type' fields are the same as described in Section 372 3.10 of [2]. The 'SPI Size' field MUST be set to 0 to indicate that 373 the SPI is not present in this message. The 'Protocol ID' MUST be 374 set to 0, since the notification is not specific to a particular 375 security association. 377 The 'Payload Length' field is set to the length in octets of the 378 entire payload, including the generic payload header. The 'Notify 379 Message Type' field is set to indicate the REDIRECT_SUPPORTED payload 380 . 382 7.2. REDIRECT 384 The REDIRECT payload is included in an IKE_SA_INIT response from the 385 responder or an INFORMATIONAL message from the responder, when the 386 responder wants to redirect the initiator to another VPN gateway. 387 The message includes the new responder's IP address or DNS name. 389 1 2 3 390 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 1 391 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 392 | Next Payload |C| RESERVED | Payload Length | 393 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 394 | Protocol ID | SPI Size (=0) | Notify Message Type | 395 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 396 | GW Ident Type | GW Ident Len | | 397 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 398 ~ New Responder GW Identity ~ 399 | | 400 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 401 | | 402 ~ Nonce Data ~ 403 | | 404 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 406 The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size' and 407 the 'Notify Message Type' fields are the same as described in Section 408 3.10 of [2]. The 'SPI Size' field MUST be set to 0 to indicate that 409 the SPI is not present in this message. The 'Protocol ID' MUST be 410 set to 0, since the notification is not specific to a particular 411 security association. 413 The 'Payload Length' field is set to the length in octets of the 414 entire payload, including the generic payload header. 'Notify 415 Message Type' field is set to indicate the REDIRECT payload . The 'GW Identity Type' field indicates the 417 type of information that is sent to identify the new VPN gateway. 418 The following values are valid in the REDIRECT payload. 420 1 - IPv4 address of the new VPN gateway 421 2 - IPv6 address of the new VPN gateway 422 3 - FQDN of the new VPN gateway 424 The 'GW Ident Len' field is set to the length of the gateway identity 425 information. The identity of the new VPN gateway is carried in the 426 'New Responder GW Identity' field. The IPv4 address, the IPv6 427 address or the FQDN of the new VPN gateway MUST be encoded as 428 described in section 3.5 of [2]. 430 The 'Nonce Data' field carries the nonce data from the Ni payload 431 sent by the initiator. The size of the nonce MUST be between 16 and 432 256 bytes as described in Section 3.9 of [2]. The 'Nonce Data' field 433 is present in the REDIRECT payload only when the REDIRECT payload is 434 sent in the IKE_SA_INIT response message. It MUST NOT be included in 435 the REDIRECT payload if sent in an IKE_AUTH response or in a gateway- 436 initiated redirect message. 438 7.3. REDIRECTED_FROM 440 The REDIRECTED_FROM message type is included in the IKE_SA_INIT 441 request from the initiator to the new VPN gateway to indicate the IP 442 address of the original VPN gateway that redirected the initiator. 443 The original VPN gateway's IP address is included in the message. 445 1 2 3 446 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 1 447 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 448 | Next Payload |C| RESERVED | Payload Length | 449 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 450 | Protocol ID | SPI Size (=0) | Notify Message Type | 451 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 452 | GW Ident Type | GW Ident Len | | 453 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 454 ~ Original Responder GW Identity ~ 455 | | 456 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 458 The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size' and 459 the 'Notify Message Type' fields are the same as described in Section 460 3.10 of [2] The 'SPI Size' field MUST be set to 0 to indicate that 461 the SPI is not present in this message. The 'Protocol ID' MUST be 462 set to 0, since the notification is not specific to a particular 463 security association. 465 The 'Payload Length' field is set to the length in octets of the 466 entire payload, including the generic payload header. The 'Notify 467 Message Type' field is set to indicate the REDIRECTED_FROM payload 468 . The 'GW Identity Type' field 469 indicates the type of information that is sent to identify the new 470 VPN gateway. The following values are valid in the REDIRECTED_FROM 471 payload. 473 1 - IPv4 address of the original VPN gateway 474 2 - IPv6 address of the original VPN gateway 476 The 'GW Ident Len' field is set to the length of the gateway identity 477 information. The identity of the original VPN gateway is carried in 478 the 'Original Responder GW Identity' field. 480 8. Use of the Redirect Mechanism between IKEv2 Peers 482 The Redirect mechanism described in this document is mainly intended 483 for use in client-gateway scenarios. However, the mechanism can also 484 be used between any two IKEv2 peers. But this protocol is 485 asymmetric, meaning that only the original responder can redirect the 486 original initiator to another server. 488 9. Security Considerations 490 An eavesdropper on the path between VPN client and server may send a 491 redirect to the client upon receiving an IKE_SA_INIT message from 492 this client. This is no problem regarding DoS attacks for the VPN 493 connection, since an on-path-attacker can as well drop the 494 IKE_SA_INIT requests to prevent VPN access for the client. But an 495 eavesdropper on the path between VPN client and server can redirect a 496 large number of clients to a victim, which is then flooded with 497 IKE_SA_INIT requests. Flooding only happens if many clients initiate 498 IKEv2 exchange at almost the same time, which is considered a rare 499 event. However, this may happen if a Home Agent/VPN server is 500 shutdown for maintenance and all clients need to re-establish VPN 501 connections with another Home Agent/VPN server or if the on-path 502 attacker forces all IPsec security associations to expire by dropping 503 all received IKEv2 messages. 505 The use of REDIRECTED_FROM payload is intended to discourage a rogue 506 VPN gateway from redirecting a large number of VPN clients to a 507 particular VPN gateway. It does not prevent such a DoS attack. 509 The redirect mechanism MUST NOT update any state on the client apart 510 from the VPN gateway information. When used with Mobile IPv6, care 511 must be taken to ensure that the home agent information that the 512 mobile node has configured is not modified wrongly by the redirect 513 message. 515 The client could end up getting redirected multiple times in a 516 sequence, either because of wrong configuration or a DoS attack. The 517 client could even end up in a loop with two or more gateways 518 redirecting the client to each other. This could deny service to the 519 client. To prevent this, the client should be configured not to 520 accept more a certain number of redirects within a short time period. 521 This should be configurable on the client. 523 Redirecting based on the unauthenticated identities from the client 524 might leak out information about the user when an active attacker, 525 pretending to be a VPN client can get information to which gateway 526 the real user was redirected to. If redirection is based on some 527 internal information of the user, it might leak information to 528 attacker about the user which might not available otherwise. To 529 prevent these kind of attacks, redirection based on unauthenticated 530 ID should be avoided and should be done only after the client has 531 also authenticated itself. 533 10. IANA Considerations 535 This document defines three new IKEv2 Notification Message types as 536 described in Section 7. The three Notify Message Types must be 537 assigned values between 16396 and 40959. 539 o REDIRECT_SUPPORTED 540 o REDIRECT 541 o REDIRECTED_FROM 543 This document creates a new namespace called the "Gateway Identity 544 Type". This is used to indicate the type of information regarding 545 the VPN gateway that is carried in the REDIRECT (Section 7.2) and 546 REDIRECTED_FROM (Section 7.3) Notification payloads. The following 547 values are assigned. 549 1 - IPv4 address of the new VPN gateway 550 2 - IPv6 address of the new VPN gateway 551 3 - FQDN of the new VPN gateway 553 Values '0', and 4-255 are reserved. New values can be allocated by 554 expert review. A specification that extends this registry MUST also 555 mention which of the new values are valid in which Notification 556 payload. 558 11. Acknowledgements 560 The use of anycast address with IKEv2 was first described in [7]. It 561 was then added to an early draft version of RFC 5026 and later 562 removed before the RFC was published. Therefore the authors of [7] 563 and RFC 5026 are acknowledged. 565 Thanks to Pasi Eronen, with whom the solution described in this 566 document was extensively discussed. Thanks to Tero Kivinen for 567 suggesting the use of REDIRECTED_FROM payload and other comments 568 which helped improve the document. The authors would also like to 569 thank Yaron Sheffer, Sunil Kumar, Fan Zhao, Yoav Nir, Richard 570 Graveman, Kanagavel Rajan, Srini Addepalli, and Arnaud Ebalard for 571 their reviews and comments. 573 12. References 575 12.1. Normative References 577 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 578 Levels", BCP 14, RFC 2119, March 1997. 580 [2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC 4306, 581 December 2005. 583 12.2. Informative References 585 [3] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in 586 IPv6", RFC 3775, June 2004. 588 [4] Giaretta, G., Kempf, J., and V. Devarapalli, "Mobile IPv6 589 Bootstrapping in Split Scenario", RFC 5026, October 2007. 591 [5] Haley, B., Devarapalli, V., Deng, H., and J. Kempf, "Mobility 592 Header Home Agent Switch Message", RFC 5142, January 2008. 594 [6] Eronen, P. and J. Korhonen, "Multiple Authentication Exchanges 595 in the Internet Key Exchange (IKEv2) Protocol", RFC 4739, 596 November 2006. 598 [7] Weniger, K. and F. Dupont, "IKEv2-based Home Agent Assignment in 599 Mobile IPv6/NEMO Bootstrapping", draft-dupont-ikev2-haassign-02 600 (work in progress), January 2007. 602 [8] Kent, S. and K. Seo, "Security Architecture for the Internet 603 Protocol", RFC 4301, December 2005. 605 Authors' Addresses 607 Vijay Devarapalli 608 WiChorus 609 3590 North First St 610 San Jose, CA 95134 611 USA 613 Email: vijay@wichorus.com 615 Kilian Weniger 617 Email: kilian.weniger@googlemail.com