idnits 2.17.1 draft-ietf-pim-sm-linklocal-08.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- ** The document seems to lack a License Notice according IETF Trust Provisions of 28 Dec 2009, Section 6.b.i or Provisions of 12 Sep 2009 Section 6.b -- however, there's a paragraph with a matching beginning. Boilerplate error? (You're using the IETF Trust Provisions' Section 6.b License Notice from 12 Feb 2009 rather than one of the newer Notices. See https://trustee.ietf.org/license-info/.) 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 (Using the creation date from RFC4601, updated by this document, for RFC5378 checks: 2000-07-17) -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (April 14, 2009) is 5489 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) ** Obsolete normative reference: RFC 4601 (Obsoleted by RFC 7761) ** Obsolete normative reference: RFC 4835 (Obsoleted by RFC 7321) -- Obsolete informational reference (is this intentional?): RFC 2401 (Obsoleted by RFC 4301) -- Obsolete informational reference (is this intentional?): RFC 4306 (Obsoleted by RFC 5996) -- Obsolete informational reference (is this intentional?): RFC 3547 (Obsoleted by RFC 6407) Summary: 3 errors (**), 0 flaws (~~), 1 warning (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 PIM Working Group W. Atwood 3 Internet-Draft Concordia University/CSE 4 Updates: 4601 (if approved) S. Islam 5 Intended status: Standards Track INRS Energie, Materiaux et 6 Expires: October 16, 2009 Telecommunications 7 M. Siami 8 Concordia University/CIISE 9 April 14, 2009 11 Authentication and Confidentiality in PIM-SM Link-local Messages 12 draft-ietf-pim-sm-linklocal-08 14 Status of this Memo 16 This Internet-Draft is submitted to IETF in full conformance with the 17 provisions of BCP 78 and BCP 79. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as Internet- 22 Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet-Drafts as reference 27 material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt. 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 This Internet-Draft will expire on October 16, 2009. 37 Copyright Notice 39 Copyright (c) 2009 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents in effect on the date of 44 publication of this document (http://trustee.ietf.org/license-info). 45 Please review these documents carefully, as they describe your rights 46 and restrictions with respect to this document. 48 Abstract 50 RFC 4601 mandates the use of IPsec to ensure authentication of the 51 link-local messages in the Protocol Independent Multicast - Sparse 52 Mode (PIM-SM) routing protocol. This document specifies mechanisms 53 to authenticate the PIM-SM link-local messages using the IP security 54 (IPsec) Encapsulating Security Payload (ESP) or (optionally) the 55 Authentication Header (AH). It specifies optional mechanisms to 56 provide confidentiality using the ESP. Manual keying is specified as 57 the mandatory and default group key management solution. To deal 58 with issues of scalability and security that exist with manual 59 keying, an optional support for automated group key management 60 mechanism is provided. However, the procedures for implementing 61 automated group key management are left to other documents. This 62 document updates RFC 4601. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 67 1.1. Goals and Non-goals . . . . . . . . . . . . . . . . . . . 4 68 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 69 3. Transport Mode vs. Tunnel Mode . . . . . . . . . . . . . . . . 5 70 4. Authentication . . . . . . . . . . . . . . . . . . . . . . . . 5 71 5. Confidentiality . . . . . . . . . . . . . . . . . . . . . . . 6 72 6. IPsec Requirements . . . . . . . . . . . . . . . . . . . . . . 6 73 7. Key Management . . . . . . . . . . . . . . . . . . . . . . . . 8 74 7.1. Manual Key Management . . . . . . . . . . . . . . . . . . 8 75 7.2. Automated Key Management . . . . . . . . . . . . . . . . . 8 76 7.3. Communications Patterns . . . . . . . . . . . . . . . . . 9 77 7.4. Neighbor Relationships . . . . . . . . . . . . . . . . . . 11 78 8. Number of Security Associations . . . . . . . . . . . . . . . 11 79 9. Rekeying . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 80 9.1. Manual Rekeying Procedure . . . . . . . . . . . . . . . . 13 81 9.2. KeyRollover Interval . . . . . . . . . . . . . . . . . . . 14 82 9.3. Rekeying Interval . . . . . . . . . . . . . . . . . . . . 14 83 10. IPsec Protection Barrier and SPD/GSPD . . . . . . . . . . . . 14 84 10.1. Manual Keying . . . . . . . . . . . . . . . . . . . . . . 15 85 10.1.1. SAD Entries . . . . . . . . . . . . . . . . . . . . . 15 86 10.1.2. SPD Entries . . . . . . . . . . . . . . . . . . . . . 15 87 10.2. Automatic Keying . . . . . . . . . . . . . . . . . . . . . 15 88 10.2.1. SAD Entries . . . . . . . . . . . . . . . . . . . . . 15 89 10.2.2. GSPD Entries . . . . . . . . . . . . . . . . . . . . 15 90 10.2.3. PAD Entries . . . . . . . . . . . . . . . . . . . . . 16 91 11. Security Association Lookup . . . . . . . . . . . . . . . . . 16 92 12. Activating the Anti-replay Mechanism . . . . . . . . . . . . . 17 93 13. Implementing a Security Policy Database per Interface . . . . 17 94 14. Extended Sequence Number . . . . . . . . . . . . . . . . . . . 18 95 15. Security Considerations . . . . . . . . . . . . . . . . . . . 18 96 16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 97 17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19 98 18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19 99 18.1. Normative References . . . . . . . . . . . . . . . . . . . 19 100 18.2. Informative References . . . . . . . . . . . . . . . . . . 20 101 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 103 1. Introduction 105 All the PIM-SM [RFC4601] control messages have IP protocol number 106 103. These messages are either unicast, or multicast with TTL = 1. 107 The source address used for unicast messages is a domain-wide 108 reachable address. For the multicast messages, a link-local address 109 of the interface on which the message is being sent is used as the 110 source address and a special multicast address, ALL_PIM_ROUTERS 111 (224.0.0.13 in IPv4 and ff02::d in IPv6) is used as the destination 112 address. These messages are called link-local messages. Hello, 113 Join/Prune and Assert messages are included in this category. A 114 forged link-local message may be sent to the ALL_PIM_ROUTERS 115 multicast address by an attacker. This type of message affects the 116 construction of the distribution tree [RFC4601]. The effects of 117 these forged messages are outlined in section 6.1 of [RFC4601]. Some 118 of the effects are very severe, whereas some are minor. 120 PIM-SM version 2 was originally specified in RFC 2117, and revised in 121 RFC 2362 and RFC 4601. RFC 4601 obsoletes RFC 2362, and corrects a 122 number of deficiencies. The Security Considerations section of RFC 123 4601 is based primarily on the Authentication Header (AH) 124 specification described in RFC 4302 [RFC4302]. 126 Securing the unicast messages can be achieved by the use of a normal 127 unicast IPsec Security Association between the two communicants. 129 This document focuses on the security issues for link-local messages. 130 It provides some guidelines to take advantage of the new permitted AH 131 functionality in RFC 4302 and the new permitted ESP functionality in 132 RFC 4303 [RFC4303], and to bring the PIM-SM specification into 133 alignment with the new AH and ESP specifications. In particular, in 134 accordance with RFC 4301, the use of ESP is made mandatory and AH is 135 specified as optional. This document specifies manual key management 136 as mandatory to implement, i.e., that all implementations MUST 137 support, and provides the necessary structure for an automated key 138 management protocol that the PIM routers may use. 140 1.1. Goals and Non-goals 142 The primary goal for link-local security is to provide data origin 143 authentication for each link-local message. A secondary goal is to 144 ensure that communication only happens between legitimate peers 145 (i.e., adjacent routers). An optional goal is to provide data 146 confidentiality for the link-local messages. 148 The first goal implies that each router has a unique identity. It is 149 possible (but not mandatory) that this identity will be based on the 150 unicast identity of the router. (The unicast identity could be, for 151 example, based on some individually-configured property of the 152 router, or be part of a region-wide public key infrastructure.) The 153 existence of this unique identity is assumed in this specification, 154 but procedures for establishing it are out-of-scope for this 155 document. 157 The second goal implies that there is some form of "adjacency matrix" 158 that controls the establishment of security associations among 159 adjacent multicast routers. For manual keying, this control will be 160 exercised by the Administrator of the router(s), through the setting 161 of initialization parameters. For automated keying, the existence of 162 this control will be reflected by the contents of the Peer 163 Authorization Database (PAD) and the Group Security Policy Database 164 (GSPD) in each router. Procedures for controling the adjacency and 165 building the asssociated PAD and GSPD are out-of-scope for this 166 document. 168 2. Terminology 170 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 171 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 172 document are to be interpreted as described in RFC 2119 [RFC2119]. 173 They indicate requirement levels for compliant PIM-SM 174 implementations. 176 3. Transport Mode vs. Tunnel Mode 178 All implementations conforming to this specification MUST support 179 transport mode SA to provide required IPsec security to PIM-SM link- 180 local messages. They MAY also support tunnel mode SA to provide 181 required IPsec security to PIM-SM link-local messages. If tunnel 182 mode is used, both destination address preservation and source 183 address preservation MUST be used, as described in Section 3.1 of RFC 184 5374 [RFC5374]. 186 4. Authentication 188 Implementations conforming to this specification MUST support 189 authentication for PIM-SM link-local messages. Implementations 190 conforming to this specification MUST support HMAC-SHA1. 192 In order to provide authentication to PIM-SM link-local messages, 193 implementations MUST support ESP [RFC4303] and MAY support AH 194 [RFC4302]. 196 If ESP in transport mode is used, it will only provide authentication 197 to PIM-SM protocol packets excluding the IP header, extension 198 headers, and options. 200 If AH in transport mode is used, it will provide authentication to 201 PIM-SM protocol packets, selected portions of the IP header, 202 extension headers and options. 204 When authentication for PIM-SM link-local messages is enabled, 206 o PIM-SM link-local packets that are not protected with AH or ESP 207 MUST be silently discarded. 209 o PIM-SM link-local packets that fail the authentication checks MUST 210 be silently discarded. 212 5. Confidentiality 214 Implementations conforming to this specification SHOULD support 215 confidentiality for PIM-SM. Implementations supporting 216 confidentiality MUST support AES-CBC with a 128-bit key. 218 If confidentiality is provided, ESP MUST be used. 220 When PIM-SM confidentiality is enabled, 222 o PIM-SM packets that are not protected with ESP MUST be silently 223 discarded. 225 o PIM-SM packets that fail the confidentiality checks MUST be 226 silently discarded. 228 Note that since authentication MUST be supported by a conforming 229 implementation, the combination of NON-NULL Encryption and NULL 230 Authentication is NOT permitted. 232 6. IPsec Requirements 234 In order to implement this specification, the following IPsec 235 capabilities are required. 237 Transport mode 238 IPsec in transport mode MUST be supported. 240 Multiple Security Policy Databases (SPDs) 241 The implementation MUST support multiple SPDs with an SPD 242 selection function that provides an ability to choose a specific 243 SPD based on interface. 245 Selectors 246 The implementation MUST be able to use source address, destination 247 address, protocol, and direction as selectors in the SPD. 249 Interface ID tagging 250 The implementation MUST be able to tag the inbound packets with 251 the ID of the interface (physical or virtual) via which it 252 arrived. 254 Manual key support 255 Manually configured keys MUST be able to secure the specified 256 traffic. 258 Encryption and authentication algorithms 259 Encryption and authentication algorithm requirements described in 260 RFC 4835 [RFC4835] apply when ESP and AH are used to protect 261 PIM-SM. Implementations MUST support ESP-NULL, and if providing 262 confidentiality MUST support the RFC4835 [RFC4835] required ESP 263 transforms providing confidentiality. However, in any case, 264 implementations MUST NOT allow the user to choose a stream cipher 265 or block mode cipher in counter mode for use with manual keys. 267 Encapsulation of ESP packet 268 IP encapsulation of ESP packets MUST be supported. For 269 simplicity, UDP encapsulation of ESP packets SHOULD NOT be used. 271 If the automatic keying features of this specification are 272 implemented, the following additional IPsec capabilities are 273 required: 275 Group Security Policy Database (GSPD) 276 The implementation MUST support the GSPD that is described in RFC 277 5374 [RFC5374]. 279 Multiple Group Security Policy Databases 280 The implementation MUST support multiple GSPDs with a GSPD 281 selection function that provides an ability to choose a specific 282 GSPD based on interface. 284 Selectors 285 The implementation MUST be able to use source address, destination 286 address, protocol and direction as selectors in the GSPD. 288 7. Key Management 290 All the implementations MUST support manual configuration of the 291 Security Associations (SAs) that will be used to authenticate PIM-SM 292 link-local messages. This does not preclude the use of a negotiation 293 protocol such as the Internet Key Exchange (IKE) [RFC4306] or Group 294 Secure Association Key Management Protocol (GSAKMP) [RFC4535] to 295 establish SAs. 297 7.1. Manual Key Management 299 To establish the SAs at PIM-SM routers, manual key configuration will 300 be feasible when the number of peers (directly connected routers) is 301 small. The Network Administrator will configure a router manually 302 during its boot up process. At that time, the authentication method 303 and the choice of keys SHOULD be configured. The Security 304 Association Database (SAD) entry will be created. The Network 305 Administrator will also configure the Security Policy Database of a 306 router to ensure the use of the associated SA while sending a link- 307 local message. 309 7.2. Automated Key Management 311 All the link-local messages of the PIM-SM protocol are sent to the 312 destination address, ALL_PIM_ROUTERS, which is a multicast address. 313 By using the sender address in conjunction with the destination 314 address for Security Association lookup, link-local communication 315 turns into an SSM or "one to many" communication. Since IKE is based 316 on the Diffie-Hellman key agreement protocol and works only for two 317 communicating parties, it is not possible to use IKE for providing 318 the required "one to many" authentication. 320 The procedures for automated key management are not specified in this 321 document. 323 One option is to use Group Domain Of Interpretation (GDOI) [RFC3547], 324 which enables a group of users or devices to exchange encrypted data 325 using IPsec data encryption. GDOI has been developed to be used in 326 multicast applications, where the number of end users or devices may 327 be large and the end users or devices can dynamically join/leave a 328 multicast group. However, a PIM router is not expected to join/leave 329 very frequently, and the number of routers is small when compared to 330 the possible number of users of a multicast application. Moreover, 331 most of the PIM routers will be located inside the same 332 administrative domain and are considered as trusted parties. It is 333 possible that a subset of GDOI functionalities will be sufficient. 335 Another option is to use the Group Secure Association Key Management 336 Protocol (GSAKMP) [RFC4535]. 338 7.3. Communications Patterns 340 Before discussing the set of security associations that are required 341 to properly manage a multicast region that is under the control of a 342 single administration, it is necessary to understand the 343 communications patterns that will exist among the routers in this 344 region. From the perspective of a speaking router, the information 345 from that router is sent (multicast) to all of its neighbors. From 346 the perspective of a listening router, the information coming from 347 each of its neighbors is distinct from the information coming from 348 every other router to which it is directly connected. Thus an 349 administrative region contains many (small) distinct groups, all of 350 which happen to be using the same multicast destination address 351 (e.g., ALL_PIM_ROUTERS, see Section 11), and each of which is 352 centered on the associated speaking router. 354 Consider the example configuration as shown in Figure 1. 356 R2 R3 R4 R5 R6 357 | | | | | 358 | | | | | 359 --------- --------------- 360 | | 361 | | 362 \ / 363 R1 364 / \ 365 | | 366 | | 367 --------- -------------------- 368 | | | | | 369 | | | | | 370 R7 R8 R9 R10 R11 371 | | | | | 372 | 373 | 374 ------------- 375 | | | 376 | | | 377 R12 R13 R14 379 Figure 1: Set of router interconnections 381 In this configuration, router R1 has four interfaces, and is the 382 speaking router for a group whose listening routers are routers R2 383 through R11. Router R9 is the speaking router for a group whose 384 listening routers are routers R1, R8 and R10-R14. 386 From the perspective of R1 as a speaking router, if a Security 387 Association SA1 is assigned to protect outgoing packets from R1, then 388 it is necessary to distribute the key for this association to each of 389 the routers R2 through R11. Similarly, from the perspective of R9 as 390 a speaking router, if a Security Association is assigned to protect 391 the outgoing packets from R9, then it is necessary to distribute the 392 key for this association to each of the routers R1, R8, and R10 393 through R14. 395 From the perspective of R1 as a listening router, all packets 396 arriving from R2 through R11 need to be distinguished from each 397 other, to permit selecting the correct Security Association in the 398 SAD. (Packets from each of the peer routers (R2 through R11) 399 represent communication from a different speaker, with a separate 400 sequence number space, even though they are sent using the same 401 destination address.) For a multicast Security Association, RFC 4301 402 permits using the Source Address in the selection function. If the 403 source addresses used by routers R2 through R11 are globally unique, 404 then the source addresses of the peer routers are sufficient to 405 achieve the differentiation. If the sending routers use link-local 406 addresses, then these addresses are unique only on a per-interface 407 basis, and it is necessary to use the Interface ID tag as an 408 additional selector, i.e., either the selection function has to have 409 the Interface ID tag as one of its inputs, or separate SADs have to 410 be maintained for each interface. 412 If the assumption of connectivity to the key server can be made 413 (which is true in the PIM-SM case), then the Group Controller/Key 414 Server (GC/KS) that is used for the management of the keys can be 415 centrally located (and duplicated for reliability). If this 416 assumption cannot be made (i.e., in the case of adjacencies for a 417 unicast router), then some form of "local" key server must be 418 available for each group. Given that the listening routers are never 419 more than one hop away from the speaking router, the speaking router 420 is the obvious place to locate the "local" key server. As such, this 421 may be a useful approach even in the PIM-SM case. This approach has 422 the additional advantage that there is no need to duplicate the local 423 key server for reliability, since if the key server is down, it is 424 very likely that the speaking router is also down. 426 7.4. Neighbor Relationships 428 Each distinct group consists of one speaker, and the set of directly 429 connected listeners. If the decision is made to maintain one 430 Security Association per speaker (see Section 8), then the key server 431 will need to be aware of the adjacencies of each speaker. Procedures 432 for managing and distributing these adjacencies are out-of-scope for 433 this document. 435 8. Number of Security Associations 437 The number of Security Associations to be maintained by a PIM router 438 depends on the required security level and available key management. 439 This SHOULD be decided by the Network Administrator. Two different 440 ways are shown in Figure 2 and 3. It is assumed that A, B and C are 441 three PIM routers, where B and C are directly connected with A, and 442 there is no direct link between B and C. 444 | 445 B | 446 SAb ------------>| 447 SAa <------------| 448 | 449 A | 450 SAb <------------| 451 ---->| 452 / 453 SAa ------- 454 \ 455 ---->| 456 SAc <------------| 457 | 458 C | 459 SAc ------------>| 460 SAa <------------| 461 | 462 Directly connected network 464 Figure 2: Activate unique Security Association for each peer 466 The first method, shown in Figure 2, is OPTIONAL to implement. In 467 this method, each node will use a unique SA for its outbound traffic. 468 A, B, and C will use SAa, SAb, and SAc, respectively for sending any 469 traffic. Each node will include the source address when searching 470 the SAD for a match. A will use SAb and SAc for packets received 471 from B and C, respectively. The number of SAs to be activated and 472 maintained by a PIM router will be equal to the number of directly 473 connected routers, plus one for sending its own traffic. Also, the 474 addition of a PIM router in the network will require the addition of 475 another SA on every directly connected PIM router. This solution 476 will be scalable and practically feasible with an automated key 477 management protocol. However, it MAY be used with manual key 478 management, if the number of directly connected routers is small. 480 B | 481 SAo ------------>| 482 SAi <------------| 483 | 484 A | 485 SAi <------------| 486 ---->| 487 / 488 SAo ------- 489 \ 490 ---->| 491 SAi <------------| 492 | 493 C | 494 SAo ------------>| 495 SAi <------------| 496 | 497 Directly connected network 499 Figure 3: Activate two Security Associations 501 The second method, shown in Figure 3, MUST be supported by every 502 implementation. In this simple method, all the nodes will use two 503 SAs, one for sending (SAo) and the other for receiving (SAi) traffic. 504 Thus, the number of SAs is always two and will not be affected by 505 addition of a PIM router. Although two different SAs are used in 506 this method, the SA parameters (keys, Security Parameter Index (SPI), 507 etc.) for the two SAs are identical, i.e., the same information is 508 shared among all the routers in an administrative region. This 509 document RECOMMENDS the above method for manual key configuration. 510 However, it MAY also be used with automated key configuration. 512 9. Rekeying 514 To maintain the security of a link, the authentication and encryption 515 key values SHOULD be changed periodically, to limit the risk of 516 undetected key disclosure. Keys should also be changed when there is 517 a change of trusted personnel. 519 9.1. Manual Rekeying Procedure 521 The following three-step procedure SHOULD be provided to rekey the 522 routers on a link without dropping PIM-SM protocol packets or 523 disrupting the adjacency. 525 1. For every router on the link, create an additional inbound SA for 526 the interface being rekeyed using a new SPI and the new key. 528 2. For every router on the link, replace the original outbound SA 529 with one using the new SPI and key values. The SA replacement 530 operation should be atomic with respect to sending PIM-SM packets 531 on the link, so that no PIM-SM packets are sent without 532 authentication/encryption 534 3. For every router on the link, remove the original inbound SA. 536 Note that all routers on the link must complete step 1 before any 537 begin step 2. Likewise, all the routers on the link must complete 538 step 2 before any begin step 3. 540 One way to control the progression from one step to another is for 541 each router to have a configurable time constant KeyRolloverInterval. 542 After the router begins step 1 on a given link, it waits for this 543 interval and then moves to step 2. Likewise, after moving to step 2, 544 it waits for this interval and then moves to step 3. 546 In order to achieve smooth key transition, all routers on a link 547 should use the same value for KeyRolloverInterval and should initiate 548 the key rollover process within this time period. 550 At the end of this time period, all the routers on the link will have 551 a single inbound and outbound SA for PIM-SM with the new SPI and key 552 values. 554 9.2. KeyRollover Interval 556 The configured value of KeyRolloverInterval should be long enough to 557 allow the administrator to change keys on all the PIM-SM routers. As 558 this value can vary significantly depending on the implementation and 559 the deployment, it is left to the administrator to choose an 560 appropriate value. 562 9.3. Rekeying Interval 564 In keeping with the goal of reducing key exposure, the encryption and 565 authentication keys SHOULD be changed at least every 90 days. 567 10. IPsec Protection Barrier and SPD/GSPD 568 10.1. Manual Keying 570 10.1.1. SAD Entries 572 The Administrator must configure the necessary Security Associations. 573 Each SA entry has the Source Address of an authorized peer, and a 574 Destination Address of ALL_PIM_ROUTERS. Unique SPI values for the 575 manually configured SAs MUST be assigned by the Administrator, to 576 ensure that the SPI does not conflict with existing SPI values in the 577 SAD. 579 10.1.2. SPD Entries 581 The Administrator must configure the necessary SPD entries. The SPD 582 entry must ensure that any outbound IP traffic packet traversing the 583 IPsec boundary, with PIM as its next layer protocol, and sent to the 584 Destination Address of ALL_PIM_ROUTERS, is protected by ESP or AH. 585 Note that this characterization includes all the link-local messages 586 (Hello, Join/Prune, Bootstrap, Assert). 588 10.2. Automatic Keying 590 When automatic keying is used, the SA creation is done dynamically 591 using a group key management protocol. The GSPD and PAD tables are 592 configured by the Administrator. The PAD table provides the link 593 between the IPsec subsystem and the group key management protocol. 594 For automatic keying, the implementation MUST support the multicast 595 extensions described in [RFC5374]. 597 10.2.1. SAD Entries 599 All PIM routers participate in an authentication scheme that 600 identifies permitted neighbors and achieves peer authentication 601 during SA negotiation, leading to child SAs being established and 602 saved in the SAD. 604 10.2.2. GSPD Entries 606 The Administrator must configure the necessary GSPD entries for "send 607 only" directionality. This rule MUST trigger the group key 608 management protocol for a registration exchange. This exchange will 609 set up the outbound SAD entry that encrypts the multicast PIM control 610 message. Considering that this rule is "sender only", no inbound SA 611 is created in the reverse direction. 613 In addition, the registration exchange will trigger the installation 614 of the GSPD entries corresponding to each legitimate peer router, 615 with direction "receive only". Procedures for achieving the 616 registration exchange are out-of-scope for this document. 618 A router SHOULD NOT dynamically detect new neighbors as the result of 619 receiving an unauthenticated PIM-SM link-local message or an IPsec 620 packet that fails an SAD lookup. An automated key management 621 protocol SHOULD provide a means of notifying a router of new, 622 legitimate neighbors. 624 10.2.3. PAD Entries 626 The PAD will be configured with information to permit identification 627 of legitimate group members and senders (i.e., to control the 628 adjacency). Procedures for doing this are out-of-scope for this 629 document. 631 11. Security Association Lookup 633 For an SA that carries unicast traffic, three parameters (SPI, 634 destination address and security protocol type (AH or ESP)) are used 635 in the Security Association lookup process for inbound packets. The 636 SPI is sufficient to specify an SA. However, an implementation may 637 use the SPI in conjunction with the IPsec protocol type (AH or ESP) 638 for the SA lookup process. According to RFC 4301 [RFC4301], for 639 multicast SAs, in conjunction with the SPI, the destination address 640 or the destination address plus the sender address may also be used 641 in the SA lookup. This applies to both ESP and AH. The security 642 protocol field is not employed for a multicast SA lookup. 644 Given that, from the prospective of a receiving router, each peer 645 router is an independent sender and given that the destination 646 address will be the same for all senders, the receiving router MUST 647 use SPI plus destination address plus sender address when performing 648 the SA lookup. In effect, link-local communication is an SSM 649 communication that happens to use an ASM address (which is shared 650 among all the routers). 652 Given that it is always possible to distinguish a connection using 653 IPsec from a connection not using IPsec, it is recommended that the 654 address ALL_PIM_ROUTERS be used, to maintain consistency with present 655 practice. 657 Given that the sender address of an incoming packet may be only 658 locally unique (because of the use of link-local addresses), it is 659 necessary for a receiver to use the interface ID tag to determine the 660 associated SA for that sender. Therefore, this document mandates 661 that the interface ID tag, the SPI and the sender address MUST be 662 used in the SA lookup process. 664 12. Activating the Anti-replay Mechanism 666 Although link-level messages on a link constitute a multiple-sender, 667 multiple-receiver group, the use of the interface ID tag and sender 668 address for SA lookup essentially resolves the communication into a 669 separate SA for each sender/destination pair, even for the case where 670 only two SAs (with identical SA parameters) are used for the entire 671 administrative region. Therefore, the statement in the AH RFC 672 (section 2.5 of [RFC4302]) that "for a multi-sender SA, the anti- 673 replay features are not available" becomes irrelevant to the PIM-SM 674 link-local message exchange. 676 To activate the anti-replay mechanism in a unicast communication, the 677 receiver uses the sliding window protocol and it maintains a sequence 678 number for this protocol. This sequence number starts from zero. 679 Each time the sender sends a new packet, it increments this number by 680 one. In a multi-sender multicast group communication, a single 681 sequence number for the entire group would not be enough. 683 The whole scenario is different for PIM link-local messages. These 684 messages are sent to local links with TTL = 1. A link-local message 685 never propagates through one router to another. The use of the 686 sender address and the interface ID tag for SA lookup converts the 687 relationship from a multiple-sender group to multiple single-sender 688 associations. This specification RECOMMENDS activation of the anti- 689 replay mechanism only if the SAs are assigned using an automated key 690 management procedure. If manual key management is used, the anti- 691 replay SHOULD NOT be activated. 693 If an existing router has to restart, in accordance with RFC 4303 694 [RFC4303], the sequence number counter at the sender MUST be 695 correctly maintained across local reboots, etc., until the key is 696 replaced. 698 13. Implementing a Security Policy Database per Interface 700 RFC 4601 suggests that it may be desirable to implement a separate 701 Security Policy Database (SPD) for each router interface. The use of 702 link-local addresses in certain circumstances implies that 703 differentiation of ambiguous speaker addresses requires the use of 704 the interface ID tag in the SA lookup. One way to do this is through 705 the use of multiple SPDs. Alternatively, the interface ID tag may be 706 a specific component of the selector algorithm. This is in 707 conformance with RFC 4301, which explicitly removes the requirement 708 for separate SPDs that was present in RFC 2401 [RFC2401]. 710 14. Extended Sequence Number 712 In the [RFC4302], there is a provision for a 64-bit Extended Sequence 713 Number (ESN) as the counter of the sliding window used in the anti- 714 replay protocol. Both the sender and the receiver maintain a 64-bit 715 counter for the sequence number, although only the lower order 32 716 bits are sent in the transmission. In other words, it will not 717 affect the present header format of AH. If ESN is used, a sender 718 router can send 2^64 -1 packets without any intervention. This 719 number is very large, and from a PIM router's point of view, a PIM 720 router can never exceed this number in its lifetime. This makes it 721 reasonable to permit manual configuration for a small number of PIM 722 routers, since the sequence number will never roll over. For this 723 reason, when manual configuration is used, ESN SHOULD be deployed as 724 the sequence number for the sliding window protocol. In addition, 725 when an ESN is used with a manually-keyed SA, it MUST be saved over a 726 reboot, along with an indication of which sequence numbers have been 727 used. 729 15. Security Considerations 731 The whole document considers the security issues of PIM link-local 732 messages and proposes a mechanism to protect them. 734 Limitations of manual keys: 736 The following are some of the known limitations of the usage of 737 manual keys. 739 o If replay protection cannot be provided, the PIM routers will not 740 be secured against all the attacks that can be performed by 741 replaying PIM packets. 743 o Manual keys are usually long lived (changing them often is a 744 tedious task). This gives an attacker enough time to discover the 745 keys. 747 o As the administrator is manually configuring the keys, there is a 748 chance that the configured keys are weak (there are known weak 749 keys for DES/3DES at least). 751 Impersonation attacks: 753 The usage of the same key on all the PIM routers connected to a link 754 leaves them all insecure against impersonation attacks if any one of 755 the PIM routers is compromised, malfunctioning, or misconfigured. 757 Detailed analysis of various vulnerabilities of routing protocols is 758 provided in RFC 4593 [RFC4593]. For further discussion of PIM-SM and 759 multicast security the reader is referred to RFC 5294 [RFC5294], RFC 760 4609 [RFC4609] and the Security Considerations section of RFC 4601 761 [RFC4601]. 763 16. IANA Considerations 765 This document has no actions for IANA. 767 17. Acknowledgements 769 The structure and text of this document draw heavily from RFC 4552 770 [RFC4552]. The authors of this document thank M. Gupta and N. Melam 771 for permisison to do this. 773 The quality of this document was substiantially improved after SECDIR 774 pre-review by Brian Weis. 776 18. References 778 18.1. Normative References 780 [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 781 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 782 Protocol Specification (Revised)", RFC 4601, August 2006. 784 [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, 785 December 2005. 787 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 788 Requirement Levels", BCP 14, RFC 2119, March 1997. 790 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 791 Internet Protocol", RFC 4301, December 2005. 793 [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", 794 RFC 4303, December 2005. 796 [RFC4835] Manral, V., "Cryptographic Algorithm Implementation 797 Requirements for Encapsulating Security Payload (ESP) and 798 Authentication Header (AH)", RFC 4835, April 2007. 800 [RFC5374] Weis, B., Gross, G., and D. Ignjatic, "Multicast 801 Extensions to the Security Architecture for the Internet 802 Protocol", RFC 5374, November 2008. 804 18.2. Informative References 806 [RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the 807 Internet Protocol", RFC 2401, November 1998. 809 [RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", 810 RFC 4306, December 2005. 812 [RFC4535] Harney, H., Meth, U., Colegrove, A., and G. Gross, 813 "GSAKMP: Group Secure Association Key Management 814 Protocol", RFC 4535, June 2006. 816 [RFC3547] Baugher, M., Weis, B., Hardjono, T., and H. Harney, "The 817 Group Domain of Interpretation", RFC 3547, July 2003. 819 [RFC4593] Barbir, A., Murphy, S., and Y. Yang, "Generic Threats to 820 Routing Protocols", RFC 4593, October 2006. 822 [RFC5294] Savola, P. and J. Lingard, "Host Threats to Protocol 823 Independent Multicast (PIM)", RFC 5294, August 2008. 825 [RFC4609] Savola, P., Lehtonen, R., and D. Meyer, "Protocol 826 Independent Multicast - Sparse Mode (PIM-SM) Multicast 827 Routing Security Issues and Enhancements", RFC 4609, 828 October 2006. 830 [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality 831 for OSPFv3", RFC 4552, June 2006. 833 Authors' Addresses 835 J. William Atwood 836 Concordia University/CSE 837 1455 de Maisonneuve Blvd, West 838 Montreal, QC H3G 1M8 839 Canada 841 Phone: +1(514)848-2424 ext3046 842 Email: bill@cse.concordia.ca 843 URI: http://users.encs.concordia.ca/~bill 844 Salekul Islam 845 INRS Energie, Materiaux et Telecommunications 846 800, de La Gauchetiere, suite 800 847 Montreal, QC H5A 1K6 848 Canada 850 Email: Salekul.Islam@emt.inrs.ca 851 URI: http://users.encs.concordia.ca/~salek_is 853 Maziar Siami 854 Concordia University/CIISE 855 1455 de Maisonneuve Blvd, West 856 Montreal, QC H3G 1M8 857 Canada 859 Email: m_siamis@ciise.concordia.ca