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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) -- Obsolete informational reference (is this intentional?): RFC 5226 (ref. '9') (Obsoleted by RFC 8126) Summary: 2 errors (**), 0 flaws (~~), 1 warning (==), 4 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: January 31, 2010 July 30, 2009 7 Redirect Mechanism for IKEv2 8 draft-ietf-ipsecme-ikev2-redirect-12.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 contain material 14 from IETF Documents or IETF Contributions published or made publicly 15 available before November 10, 2008. The person(s) controlling the 16 copyright in some of this material may not have granted the IETF 17 Trust the right to allow modifications of such material outside the 18 IETF Standards Process. Without obtaining an adequate license from 19 the person(s) controlling the copyright in such materials, this 20 document may not be modified outside the IETF Standards Process, and 21 derivative works of it may not be created outside the IETF Standards 22 Process, except to format it for publication as an RFC or to 23 translate it into languages other than English. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF), its areas, and its working groups. Note that 27 other groups may also distribute working documents as Internet- 28 Drafts. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 The list of current Internet-Drafts can be accessed at 36 http://www.ietf.org/ietf/1id-abstracts.txt. 38 The list of Internet-Draft Shadow Directories can be accessed at 39 http://www.ietf.org/shadow.html. 41 This Internet-Draft will expire on January 31, 2010. 43 Copyright Notice 45 Copyright (c) 2009 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 in effect on the date of 50 publication of this document (http://trustee.ietf.org/license-info). 51 Please review these documents carefully, as they describe your rights 52 and restrictions with respect to this document. 54 Abstract 56 IKEv2 is a protocol for setting up Virtual Private Network (VPN) 57 tunnels from a remote location to a gateway so that the VPN client 58 can access services in the network behind the gateway. This document 59 defines an IKEv2 extension that allows an overloaded VPN gateway or a 60 VPN gateway that is being shot down for maintenance to redirect the 61 VPN client to attach to another gateway. The proposed mechanism can 62 also be used in Mobile IPv6 to enable the home agent to redirect the 63 mobile node to another home agent. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 68 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 69 3. IKEv2 Initial Exchange with Redirect . . . . . . . . . . . . . 3 70 4. Use of Anycast Addresses with the Redirect Mechanism . . . . . 5 71 5. Redirect During an Active Session . . . . . . . . . . . . . . 6 72 6. Redirect During IKE_AUTH Exchange . . . . . . . . . . . . . . 7 73 7. Handling Redirect Loops . . . . . . . . . . . . . . . . . . . 8 74 8. Using the Redirect Mechanism with Mobile IPv6 . . . . . . . . 8 75 9. Redirect Messages . . . . . . . . . . . . . . . . . . . . . . 9 76 9.1. REDIRECT_SUPPORTED . . . . . . . . . . . . . . . . . . . . 9 77 9.2. REDIRECT . . . . . . . . . . . . . . . . . . . . . . . . . 10 78 9.3. REDIRECTED_FROM . . . . . . . . . . . . . . . . . . . . . 11 79 10. Use of the Redirect Mechanism between IKEv2 Peers . . . . . . 12 80 11. Security Considerations . . . . . . . . . . . . . . . . . . . 12 81 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 82 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 83 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 84 14.1. Normative References . . . . . . . . . . . . . . . . . . . 14 85 14.2. Informative References . . . . . . . . . . . . . . . . . . 14 86 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 88 1. Introduction 90 IKEv2 [2] is used for setting up IPsec [8] based VPNs. The IP 91 address of the VPN gateway can be configured on the VPN client. But 92 this does not scale well, when the number of VPN gateways is large. 93 Dynamic discovery of VPN gateways using DNS is quite widely used too. 94 However, using DNS is not flexible when it comes to assigning a VPN 95 gateway to the VPN client based on the load on the VPN gateways. The 96 VPN client typically tries to connect to the IP address of the VPN 97 gateway that appears first in the DNS response. If the VPN tunnel 98 setup fails, then the VPN client tries to attach to the other VPN 99 gateways returned in the DNS response. 101 This document proposes a redirect mechanism for IKEv2 that enables a 102 VPN gateway to redirect the VPN client to another VPN gateway, for 103 example, based on the load condition. The redirect can be done 104 during the IKE_SA_INIT or the IKE_AUTH exchange. Gateway-initiated 105 redirect in the middle of a session is also supported. The redirect 106 mechanism can also be used in conjunction with anycast addresses. In 107 this case, anycast address for the cluster of VPN gateways is stored 108 in the DNS instead of a list of unicast IP addresses of the VPN 109 gateways. 111 The redirect can also happen because of administrative or optimal 112 routing reasons. This document does not attempt to provide an 113 exhaustive list of reasons for redirecting a VPN client to another 114 VPN gateway. 116 2. Terminology 118 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 119 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 120 document are to be interpreted as described in [1]. 122 3. IKEv2 Initial Exchange with Redirect 124 This section describes the use of Redirect mechanism during the 125 IKE_SA_INIT exchange. Gateway-initiated redirect during an active 126 session and the use of redirect during IKE_AUTH exchange are 127 explained in subsequent sections. 129 The VPN client indicates support for the IKEv2 redirect mechanism and 130 the willingness to be redirected by including a REDIRECT_SUPPORTED 131 notification message in the initial IKE_SA_INIT request. (See 132 Section 9.1). The gateway MUST keep track of those clients that 133 indicated support for the redirect mechanism and those that didn't. 135 To redirect an IKEv2 session to another VPN gateway, the VPN gateway 136 that initially received the IKE_SA_INIT request selects another VPN 137 gateway (how the selection is made is beyond the scope of this 138 document), and replies with an IKE_SA_INIT response containing a 139 REDIRECT notification message. (See Section 9.2). The notification 140 includes information about the selected VPN gateway, and the nonce 141 data from the Ni payload in the IKE_SA_INIT request. If the 142 IKE_SA_INIT request did not indicate support for the redirect 143 mechanism, the responder MUST NOT send the REDIRECT payload to the 144 VPN client. This is applicable to all REDIRECT scenarios described 145 in this document. 147 Note that when the IKE_SA_INIT response includes the REDIRECT 148 notification, the exchange does not result in the creation of an 149 IKE_SA and the responder SPI will be zero. 151 Initiator Responder (initial VPN GW) 152 --------- ------------------------- 154 (IP_I:500 -> Initial_IP_R:500) 155 HDR(A,0), SAi1, KEi, Ni, --> 156 N(REDIRECT_SUPPORTED) 158 (Initial_IP_R:500 -> IP_I:500) 159 <-- HDR(A,0), N(REDIRECT, New_GW_ID, Ni_data) 161 When the client receives the IKE_SA_INIT response, it MUST verify 162 that the nonce data matches the value sent in the IKE_SA_INIT 163 request. If the values do not match, the client MUST silently 164 discard the response (and keep waiting for another response). This 165 prevents certain Denial-of-Service attacks on the initiator that 166 could be caused by an attacker injecting IKE_SA_INIT responses with 167 the REDIRECT payloads. 169 After verifying the nonce data, the client initiates a new 170 IKE_SA_INIT exchange with the VPN gateway listed in the REDIRECT 171 payload provided this is allowed by its PAD entries. In the 172 IKE_SA_INIT exchange with the new VPN gateway, the client MUST 173 include the REDIRECTED_FROM payload. (See Section 9.3). The VPN 174 client includes the IP address of the original VPN gateway that 175 redirected the client in the REDIRECTED_FROM notification. The IKEv2 176 exchange then proceeds as it would have proceeded with the original 177 VPN gateway. 179 Initiator Responder (Selected VPN GW) 180 --------- --------------------------- 182 (IP_I:500 -> IP_R:500) 183 HDR(A,0), SAi1, KEi, Ni, --> 184 N(REDIRECTED_FROM, Initial_IP_R) 186 (IP_R:500 -> IP_I:500) 187 <-- HDR(A,B), SAr1, KEr, Nr,[CERTREQ] 189 (IP_I:500 -> IP_R:500) 190 HDR(A,B), SK {IDi, [CERT,] [CERTREQ,] 191 [IDr,]AUTH, SAi2, TSi, TSr} --> 193 (IP_R:500 -> IP_I:500) 194 <-- HDR(A,B), SK {IDr, [CERT,] AUTH, 195 SAr2, TSi, TSr} 197 The client MAY get redirected again by the new VPN gateway if the new 198 VPN gateway cannot also serve the client. The client does not have 199 to include the REDIRECT_SUPPORTED payload again in the IKE_SA_INIT 200 exchange with the new gateway after a redirect. The presence of the 201 REDIRECT_FROM payload in the IKE_SA_INIT exchange with the new 202 gateway indicates to the new gateway that the client supports the 203 redirect mechanism. 205 When the client gets redirected, it MUST use the same Peer 206 Authorization Database (PAD) and Security Policy Database (SPD) 207 entries as it would have used with the original gateway. Receiving a 208 redirect notification MUST NOT result in the modification of any PAD 209 or SPD entries. In practice, this means the new gateway either has 210 to use the same responder identity (IDr) as the original gateway, or 211 both should be part of a group of responders that are authorized by 212 the same PAD entry. See section 4.4.3.1 of [8] on using DNS names to 213 represent a group of peers in a PAD entry. 215 4. Use of Anycast Addresses with the Redirect Mechanism 217 The use of anycast addresses will avoid having to configure a 218 particular VPN gateway's IP address in the DNS. Instead, the anycast 219 address that represents the group of VPN gateways is stored in the 220 DNS. When the VPN client performs a DNS lookup for the VPN gateway, 221 it receives the anycast address of the VPN gateway in the DNS 222 response. 224 If an anycast address is returned in response to DNS resolution of an 225 FQDN, the VPN client sends the IKE_SA_INIT request to the anycast 226 address. The REDIRECT_SUPPORTED payload is included in the 227 IKE_SA_INIT request sent to the anycast address. The IKE_SA_INIT 228 request is routed to one of the VPN gateways that is part of the 229 anycast group. The VPN gateway that receives the IKE_SA_INIT request 230 responds with an IKE_SA_INIT reply from the anycast address. 232 Initiator Responder (any VPN GW) 233 --------- ------------------------- 235 (IP_I:500 -> ANYCAST:500) 236 HDR(A,0), SAi1, KEi, Ni) --> 237 N(REDIRECT_SUPPORTED) 239 (ANYCAST:500 -> IP_I:500) 240 <-- HDR(A,0), N(REDIRECT, New_GW_ID, Ni_data) 242 If the destination address on the IKE_SA_INIT request is an anycast 243 address, the VPN gateway that received the IKE_SA_INIT request MUST 244 include the REDIRECT payload to redirect the VPN client to a unicast 245 address of one of the VPN gateway. The VPN gateway that received the 246 IKE_SA_INIT request MAY redirect the client to its own unicast 247 address, if it is not overloaded. 249 The rest of the IKEv2 exchange is the same as described in Section 3. 251 5. Redirect During an Active Session 253 The redirect mechanism may also be used by a VPN gateway to redirect 254 the client to another VPN gateway in middle of a session. To 255 redirect a client, the gateway should send an INFORMATIONAL message 256 with the REDIRECT Notify payload. The REDIRECT payload MUST carry 257 information about the new VPN gateway. The gateway MUST NOT include 258 any nonce data in the REDIRECT payload, since it is a gateway- 259 initiated redirect and is protected by the IKEv2 security 260 association. When the client receives this message, it sends a 261 response (usually empty) to the gateway. The gateway retransmits the 262 redirect INFORMATIONAL message as described in [2], until it gets a 263 response. The following illustrates the INFORMATIONAL message 264 exchange for gateway-initiated redirect. 266 Initiator (VPN client) Responder (VPN GW) 267 ---------------------- ------------------ 269 <-- HDR, SK {N(REDIRECT, New_GW_ID)} 271 HDR, SK {} --> 273 The INFORMATIONAL message exchange described above is protected by 274 the existing IKEv2 SA between the client and the gateway. 276 Once the client sends an acknowledgement to the gateway, it SHOULD 277 delete the existing security associations with the old gateway by 278 sending an INFORMATIONAL message with a DELETE payload. The gateway 279 MAY also decide to delete the security associations without any 280 signaling from the client, again by sending an INFORMATIONAL message 281 with a DELETE payload. However, it should allow sufficient time for 282 the client to setup the required security associations with the new 283 security gateway. This time period should be configurable on the 284 gateway. 286 6. Redirect During IKE_AUTH Exchange 288 If the gateway decides to redirect the client during the IKE_AUTH 289 exchange, based on the identity presented by the client in the 290 IKE_AUTH request message, it prevents the creation of a CHILD SA and 291 sends the REDIRECT payload in the IKE_AUTH response. The gateway 292 MUST verify the client's AUTH payload before sending the Redirect 293 payload, and the client MUST verify the gateway's AUTH payload before 294 acting on the Redirect payload. Since the AUTH payloads were 295 exchanged and successfully verified, the IKEv2 security association 296 is valid. When the client receives the IKE_AUTH response with the 297 REDIRECT payload, it SHOULD delete the IKEv2 security association 298 with the gateway by sending an INFORMATIONAL message with a DELETE 299 payload. 301 Initiator Responder ( VPN GW) 302 --------- ------------------- 304 (IP_I:500 -> IP_R:500) 305 HDR(A,0), SAi1, KEi, Ni, --> 306 N(REDIRECTED_SUPPORTED) 308 (IP_R:500 -> IP_I:500) 309 <-- HDR(A,B), SAr1, KEr, Nr,[CERTREQ] 311 (IP_I:500 -> IP_R:500) 312 HDR(A,B), SK {IDi, [CERT,] [CERTREQ,] 313 [IDr,]AUTH, SAi2, TSi, TSr} --> 315 (IP_R:500 -> IP_I:500) 316 <-- HDR(A,B), SK {IDr, [CERT,] AUTH, 317 N(REDIRECT, New_GW_ID)} 319 In case the IKE_AUTH exchange involves EAP authentication as 320 described in Section 2.16 of RFC 4306 [2], or multiple authentication 321 methods as described in RFC 4739 [6], the gateway may decide to 322 redirect the client based on the interaction with the AAA server or 323 the external authentication server. In this case, the gateway MUST 324 send the REDIRECT Notification payload in either the first or the 325 last IKE_AUTH response. The client and the gateway MUST verify the 326 AUTH payloads as described above. 328 When EAP is used, the gateway MAY also redirect the client based on 329 the unauthenticated identity presented by the client in the first 330 IKE_AUTH exchange itself. Since EAP is used as the authentication 331 mechanism, the client does not include AUTH payload to authenticate 332 his identity, but the server still MUST include his own AUTH payload, 333 and client MUST verify it. Note that the IKEv2 SA is not created in 334 this case and the client does not have to explicitly delete the IKEv2 335 SA. 337 In all of the cases above, the client MUST accept the REDIRECT 338 notification only in the first IKE_AUTH response or the last IKE_AUTH 339 response. It MUST NOT accept the REDIRECT notification in an 340 intermediate IKE_AUTH response. 342 7. Handling Redirect Loops 344 The client could end up getting redirected multiple times in a 345 sequence, either because of wrong configuration or a DoS attack. The 346 client could even end up in a loop with two or more gateways 347 redirecting the client to each other. This could deny service to the 348 client. To prevent this, the client SHOULD be configured not to 349 accept more than a certain number of redirects (MAX_REDIRECTS) within 350 a short time period (REDIRECT_LOOP_DETECT_PERIOD) for a particular 351 IKEv2 SA setup. The default value for MAX_REDIRECTS configuration 352 variable is 5. The default value for REDIRECT_LOOP_DETECT_PERIOD 353 configuration variable is 300 seconds. Client implementations may 354 allow these variables to be configured depending on a specific 355 deployment or system configuration. 357 8. Using the Redirect Mechanism with Mobile IPv6 359 Mobile IPv6 [3] may use IKEv2 for mutual authentication between the 360 mobile node and the home agent, for home address configuration and 361 for setting up security associations for protecting Mobile IPv6 362 signaling messages [4]. The IKEv2 exchange, if IKEv2 is used, 363 precedes the exchange of Mobile IPv6 signaling messages. Therefore, 364 the mechanism described in this document can also be used by a Mobile 365 IPv6 home agent to redirect a mobile node to another home agent. 367 There is a Home Agent Switch mechanism available for redirecting a 368 mobile node to another home agent, described in [5]. The Home Agent 369 Switch mechanism can only be used after the binding cache had been 370 created at the home agent for the mobile node. The disadvantage with 371 this is that quite a bit of state is created on the home agent before 372 the mobile node can be redirected to another home agent. The 373 mechanism described in this document can be used for redirecting a 374 mobile node before any state related to the Mobile IPv6 binding is 375 created on the home agent. 377 When running IKEv2 between a Mobile IPv6 Mobile Node (MN) and Home 378 Agent (HA), redirecting the IKEv2 exchange to another HA is not 379 enough; the Mobile IPv6 signalling also needs to be sent to the new 380 HA address. The MN MAY treat the information received in the 381 IKE_SA_INIT response in similar way as it would treat HA discovery 382 information received from other unauthenticated (and potentially 383 untrustworthy) sources (such as DNS lookups not protected with 384 DNSSEC). However, if the MN has authenticated information about its 385 Home Agent, it MUST NOT be updated based on the IKE_SA_INIT response. 387 If the REDIRECT notification is received during the IKE_AUTH exchange 388 (after the HA has been authenticated; see Section 6), the MN MAY pass 389 the new address to Mobile IPv6 and treat it in similar fashion as 390 information from the Home Agent Switch Message [5]. 392 Gateway-initiated REDIRECT notifications exchanged in INFORMATIONAL 393 exchanges (see Section 5) MUST NOT result in updating any Mobile IPv6 394 state. In such cases, the Home Agent Switch Message specified in [5] 395 is used instead. 397 9. Redirect Messages 399 9.1. REDIRECT_SUPPORTED 401 The REDIRECT_SUPPORTED payload is included in the initial IKE_SA_INIT 402 request by the initiator to indicate support for the IKEv2 redirect 403 mechanism described in this document. 405 1 2 3 406 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 1 407 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 408 | Next Payload |C| RESERVED | Payload Length | 409 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 410 |Protocol ID(=0)| SPI Size (=0) | Notify Message Type | 411 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 413 The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size' and 414 the 'Notify Message Type' fields are the same as described in Section 415 3.10 of [2]. The 'SPI Size' field MUST be set to 0 to indicate that 416 the SPI is not present in this message. The 'Protocol ID' MUST be 417 set to 0, since the notification is not specific to a particular 418 security association. 420 The 'Payload Length' field is set to the length in octets of the 421 entire payload, including the generic payload header. The 'Notify 422 Message Type' field is set to indicate the REDIRECT_SUPPORTED payload 423 . 425 9.2. REDIRECT 427 The REDIRECT payload is included in an IKE_SA_INIT response from the 428 responder or an INFORMATIONAL message from the responder, when the 429 responder wants to redirect the initiator to another VPN gateway. 430 The message includes the new responder's IP address or DNS name. 432 1 2 3 433 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 1 434 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 435 | Next Payload |C| RESERVED | Payload Length | 436 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 437 |Protocol ID(=0)| SPI Size (=0) | Notify Message Type | 438 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 439 | GW Ident Type | GW Ident Len | | 440 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 441 ~ New Responder GW Identity ~ 442 | | 443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 444 | | 445 ~ Nonce Data ~ 446 | | 447 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 449 The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size' and 450 the 'Notify Message Type' fields are the same as described in Section 451 3.10 of [2]. The 'SPI Size' field MUST be set to 0 to indicate that 452 the SPI is not present in this message. The 'Protocol ID' MUST be 453 set to 0, since the notification is not specific to a particular 454 security association. 456 The 'Payload Length' field is set to the length in octets of the 457 entire payload, including the generic payload header. 'Notify 458 Message Type' field is set to indicate the REDIRECT payload . The 'GW Identity Type' field indicates the 460 type of information that is sent to identify the new VPN gateway. 461 The following values are valid in the REDIRECT payload. 463 1 - IPv4 address of the new VPN gateway 464 2 - IPv6 address of the new VPN gateway 465 3 - FQDN of the new VPN gateway 467 The 'GW Ident Len' field is set to the length of the gateway identity 468 information. The identity of the new VPN gateway is carried in the 469 'New Responder GW Identity' field. The IPv4 address, the IPv6 470 address or the FQDN of the new VPN gateway MUST be encoded as 471 described in section 3.5 of [2]. 473 The 'Nonce Data' field carries the nonce data from the Ni payload 474 sent by the initiator. The size of the nonce MUST be between 16 and 475 256 bytes as described in Section 3.9 of [2]. The 'Nonce Data' field 476 is present in the REDIRECT payload only when the REDIRECT payload is 477 sent in the IKE_SA_INIT response message. It MUST NOT be included in 478 the REDIRECT payload if sent in an IKE_AUTH response or in a gateway- 479 initiated redirect message. 481 9.3. REDIRECTED_FROM 483 The REDIRECTED_FROM notification payload is included in the 484 IKE_SA_INIT request from the initiator to the new VPN gateway to 485 indicate the IP address of the original VPN gateway that redirected 486 the initiator. The original VPN gateway's IP address is included in 487 the message. If the IKE_SA_INIT request was sent to any anycast 488 address (see Section 4), then the anycast address is included in the 489 message. This payload also serves the purpose of indicating support 490 for the redirect mechanism to the new VPN gateway after a redirect. 492 1 2 3 493 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 1 494 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 495 | Next Payload |C| RESERVED | Payload Length | 496 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 497 |Protocol ID(=0)| SPI Size (=0) | Notify Message Type | 498 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 499 | GW Ident Type | GW Ident Len | | 500 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 501 ~ Original Responder GW Identity ~ 502 | | 503 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 505 The 'Next Payload', 'Payload Length', 'Protocol ID', 'SPI Size' and 506 the 'Notify Message Type' fields are the same as described in Section 507 3.10 of [2] The 'SPI Size' field MUST be set to 0 to indicate that 508 the SPI is not present in this message. The 'Protocol ID' MUST be 509 set to 0, since the notification is not specific to a particular 510 security association. 512 The 'Payload Length' field is set to the length in octets of the 513 entire payload, including the generic payload header. The 'Notify 514 Message Type' field is set to indicate the REDIRECTED_FROM payload 515 . The 'GW Identity Type' field 516 indicates the type of information that is sent to identify the new 517 VPN gateway. The following values are valid in the REDIRECTED_FROM 518 payload. 520 1 - IPv4 address of the original VPN gateway 521 2 - IPv6 address of the original VPN gateway 523 The 'GW Ident Len' field is set to the length of the gateway identity 524 information. The identity of the original VPN gateway is carried in 525 the 'Original Responder GW Identity' field. 527 10. Use of the Redirect Mechanism between IKEv2 Peers 529 The Redirect mechanism described in this document is mainly intended 530 for use in client-gateway scenarios. However, the mechanism can also 531 be used between any two IKEv2 peers. But this protocol is 532 asymmetric, meaning that only the original responder can redirect the 533 original initiator to another server. 535 11. Security Considerations 537 An eavesdropper on the path between VPN client and server may send a 538 redirect to the client upon receiving an IKE_SA_INIT message from 539 this client. This is no problem regarding DoS attacks for the VPN 540 connection, since an on-path-attacker can as well drop the 541 IKE_SA_INIT requests to prevent VPN access for the client. But an 542 eavesdropper on the path between VPN client and server can redirect a 543 large number of clients to a victim, which is then flooded with 544 IKE_SA_INIT requests. Flooding only happens if many clients initiate 545 IKEv2 exchange at almost the same time, which is considered a rare 546 event. However, this may happen if a Home Agent/VPN server is 547 shutdown for maintenance and all clients need to re-establish VPN 548 connections with another Home Agent/VPN server or if the on-path 549 attacker forces all IPsec security associations to expire by dropping 550 all received IKEv2 messages. 552 The use of REDIRECTED_FROM payload is intended to discourage a rogue 553 VPN gateway from redirecting a large number of VPN clients to a 554 particular VPN gateway. It does not prevent such a DoS attack. 556 The redirect mechanism MUST NOT update any state on the client apart 557 from the VPN gateway information. When used with Mobile IPv6, care 558 must be taken to ensure that the home agent information that the 559 mobile node has configured is not modified wrongly by the redirect 560 message. 562 Redirecting based on the unauthenticated identities from the client 563 might leak out information about the user when an active attacker, 564 pretending to be a VPN client can get information to which gateway 565 the real user was redirected to. If redirection is based on some 566 internal information of the user, it might leak information to 567 attacker about the user which might not be available otherwise. To 568 prevent these kind of attacks, redirection based on unauthenticated 569 ID should be avoided and should be done only after the client has 570 also authenticated itself. 572 12. IANA Considerations 574 This document defines three new IKEv2 Notification Message types as 575 described in Section 9. The three Notify Message Types must be 576 assigned values between 16396 and 40959. 578 o REDIRECT_SUPPORTED 579 o REDIRECT 580 o REDIRECTED_FROM 582 This document creates a new namespace called the "Gateway Identity 583 Type". This is used to indicate the type of information regarding 584 the VPN gateway that is carried in the REDIRECT (Section 9.2) and 585 REDIRECTED_FROM (Section 9.3) Notification payloads. The following 586 values are assigned. 588 1 - IPv4 address of the new VPN gateway 589 2 - IPv6 address of the new VPN gateway 590 3 - FQDN of the new VPN gateway 592 Values '0', and 4-240 are reserved. New values can be allocated by 593 Expert Review [9]. Values 241-255 are set aside for private use. A 594 specification that extends this registry MUST also mention which of 595 the new values are valid in which Notification payload. 597 13. Acknowledgements 599 The use of anycast address with IKEv2 was first described in [7]. It 600 was then added to an early draft version of RFC 5026 and later 601 removed before the RFC was published. Therefore the authors of [7] 602 and RFC 5026 are acknowledged. 604 Thanks to Pasi Eronen, with whom the solution described in this 605 document was extensively discussed. Thanks to Tero Kivinen for 606 suggesting the use of REDIRECTED_FROM payload and other comments 607 which helped improve the document. The authors would also like to 608 thank Yaron Sheffer, Sunil Kumar, Fan Zhao, Yoav Nir, Richard 609 Graveman, Kanagavel Rajan, Srini Addepalli, Raj Singh, and Arnaud 610 Ebalard for their reviews and comments. 612 14. References 614 14.1. Normative References 616 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 617 Levels", BCP 14, RFC 2119, March 1997. 619 [2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC 4306, 620 December 2005. 622 14.2. Informative References 624 [3] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in 625 IPv6", RFC 3775, June 2004. 627 [4] Giaretta, G., Kempf, J., and V. Devarapalli, "Mobile IPv6 628 Bootstrapping in Split Scenario", RFC 5026, October 2007. 630 [5] Haley, B., Devarapalli, V., Deng, H., and J. Kempf, "Mobility 631 Header Home Agent Switch Message", RFC 5142, January 2008. 633 [6] Eronen, P. and J. Korhonen, "Multiple Authentication Exchanges 634 in the Internet Key Exchange (IKEv2) Protocol", RFC 4739, 635 November 2006. 637 [7] Weniger, K. and F. Dupont, "IKEv2-based Home Agent Assignment in 638 Mobile IPv6/NEMO Bootstrapping", draft-dupont-ikev2-haassign-02 639 (work in progress), January 2007. 641 [8] Kent, S. and K. Seo, "Security Architecture for the Internet 642 Protocol", RFC 4301, December 2005. 644 [9] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA 645 Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. 647 Authors' Addresses 649 Vijay Devarapalli 650 WiChorus 651 3590 North First St 652 San Jose, CA 95134 653 USA 655 Email: vijay@wichorus.com 657 Kilian Weniger 659 Email: kilian.weniger@googlemail.com