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Zhang 3 Internet-Draft ZTE Corporation 4 Intended status: Standards Track F. Hu 5 Expires: August 21, 2021 Individual 6 B. Xu 7 ZTE Corporation 8 M. Mishra 9 Cisco Systems 10 February 17, 2021 12 Protocol Independent Multicast - Sparse Mode (PIM-SM) Designated Router 13 (DR) Improvement 14 draft-ietf-pim-dr-improvement-11 16 Abstract 18 Protocol Independent Multicast - Sparse Mode (PIM-SM) is a widely 19 deployed multicast protocol. As deployment for the PIM protocol is 20 growing day by day, a user expects lower packet loss and faster 21 convergence regardless of the cause of the network failure. This 22 document defines an extension to the existing protocol, which 23 improves the PIM's stability with respect to packet loss and 24 convergence time when the PIM Designated Router (DR) role changes. 26 Status of This Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at https://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on August 21, 2021. 43 Copyright Notice 45 Copyright (c) 2021 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (https://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 61 1.1. Keywords . . . . . . . . . . . . . . . . . . . . . . . . 3 62 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 63 3. Protocol Specification . . . . . . . . . . . . . . . . . . . 4 64 3.1. Election Algorithm . . . . . . . . . . . . . . . . . . . 5 65 3.2. Sending Hello Messages . . . . . . . . . . . . . . . . . 7 66 3.3. Receiving Hello Messages . . . . . . . . . . . . . . . . 8 67 3.4. Working with the DRLB function . . . . . . . . . . . . . 8 68 4. PIM Hello message format . . . . . . . . . . . . . . . . . . 8 69 4.1. DR Address Option format . . . . . . . . . . . . . . . . 9 70 4.2. BDR Address Option format . . . . . . . . . . . . . . . . 9 71 4.3. Error handling . . . . . . . . . . . . . . . . . . . . . 10 72 5. Backwards Compatibility . . . . . . . . . . . . . . . . . . . 10 73 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 74 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 75 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 76 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 77 9.1. Normative References . . . . . . . . . . . . . . . . . . 11 78 9.2. Informative References . . . . . . . . . . . . . . . . . 12 79 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 81 1. Introduction 83 Multicast technology, with PIM-SM ([RFC7761]), is used widely in 84 Modern services. Some events, such as changes in unicast routes, or 85 a change in the PIM-SM DR, may cause the loss of multicast packets. 87 The PIM DR has two responsibilities in the PIM-SM protocol. For any 88 active sources on a LAN, the PIM DR is responsible for registering 89 with the Rendezvous Point (RP). Also, the PIM DR is responsible for 90 tracking local multicast listeners and forwarding data to these 91 listeners. 93 + + 94 | | 95 +-----+----+ +-----+----+ 96 | RouterA | | RouterB | 97 +-----+----+ +-----+----+ 98 | | 99 +----+----+--------+---------+---+----+ 100 | | | 101 + + + 102 Receiver1 Receiver2 Receiver3 103 Figure 1: An example of multicast network 105 The simple network in Figure 1 presents two routers (A and B) 106 connected to a shared-media LAN segment. Two different scenarios are 107 described to illustrate potential issues. 109 (a) Both routers are on the network, and RouterB is elected as the 110 DR. If RouterB then fails, multicast packets are discarded until 111 RouterA is elected as DR, and it assumes the multicast flows on the 112 LAN. As detailed in [RFC7761], a DR's election is triggered after 113 the current DR's Hello_Holdtime expires. The failure detection and 114 election procedures may take several seconds. That is too long for 115 modern multicast services. 117 (b) Only RouterA is initially on the network, making it the DR. If 118 RouterB joins the network with a higher DR Priority. Then it will be 119 elected as DR. RouterA will stop forwarding multicast packets, and 120 the flows will not recover until RouterB assumes them. 122 In either of the situations listed, many multicast packets may be 123 lost, and the quality of the services noticeably affected. To 124 increase the stability of the network this document introduces the 125 Designated DR (DR) and Backup Designated Router (BDR) options, and 126 specifies how the identity of these nodes is explicitly advertised. 128 1.1. Keywords 130 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 131 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 132 "OPTIONAL" in this document are to be interpreted as described in BCP 133 14 [RFC2119] [RFC8174] when, and only when, they appear in all 134 capitals, as shown here. 136 2. Terminology 138 Modern services: The real time multicast services, such like IPTV, 139 Net-meeting, etc. 141 Backup Designated Router (BDR): Immediately takes over all DR 142 functions ([RFC7761]) on an interface once the DR is no longer 143 present. A single BDR SHOULD be elected per interface. 145 Designated Router Other (DROther): A router which is neither a DR nor 146 a BDR. 148 0x0: 0.0.0.0 if IPv4 addresses are in use or 0:0:0:0:0:0:0:0/128 if 149 IPv6 addresses are in use. To simplify, 0x0 is used in abbreviation 150 in this draft. 152 Sticky: The DR doesn't change unnecessarily when routers, even with 153 higher priority, go down or come up. 155 3. Protocol Specification 157 The router follows the following procedures, these steps are to be 158 used when a router starts, or the interface is enabled: 160 (a). When a router first starts or its interface is enabled, it 161 includes the DR and BDR Address options with the OptionValue set to 162 0x0 in its Hello messages (Section 4). At this point the router 163 considers itself a DROther, and starts a timer set to 164 Default_Hello_Holdtime [RFC7761]. 166 (b). When the router receives Hello messages from other routers on 167 the same shared-media LAN, the router checks the value of DR/BDR 168 address option. If the value is filled with a non-zero IP address, 169 the router stores the IP address. 171 (c). After the timer expires, the router first executes the 172 algorithm defined in section 3.1. After that, the router acts as one 173 of the roles in the LAN: DR, BDR, or DROther. 175 If the router is elected the BDR, it takes on all the functions of a 176 DR as specified in [RFC7761], but it SHOULD NOT actively forward 177 multicast flows or send a register message to avoid duplication. 179 If the DR becomes unreachable on the LAN, the BDR MUST take over all 180 the DR functions, including multicast flow forwarding and sending the 181 Register messages. Mechanisms outside the scope of this 182 specification, such as [I-D.ietf-pim-bfd-p2mp-use-case] or BFD 183 Asynchronous mode [RFC5880] can be used for faster failure detection. 185 For example, there are three routers: A, B, and C. If all three were 186 in the LAN, then their DR preference would be A, B, and C, in that 187 order. Initially, only C is on the LAN, so C is DR. Later, B joins; 188 C is still the DR, and B is the BDR. Later A joins, then A becomes 189 the BDR, and B is simply DROther. 191 3.1. Election Algorithm 193 The DR and BDR election refers the DR election algorithm defined in 194 section 9.4 in [RFC2328], and updates the election function defined 195 in section 4.3.2 in [RFC7761]. 197 o The DR is elected among the DR candidates directly. If there is 198 no DR candidates, i.e., all the routers advertise the DR Address 199 options with zero OptionValue, the elected BDR will be the DR. 200 And then the BDR is elected again from the other routers in the 201 LAN. 203 o The BDR election is not sticky. Whatever there is a router that 204 advertise the BDR Address option, the router which has the highest 205 priority, expect for the elected DR, is elected as the BDR. That 206 is the BDR may be the router which has the highest priority in the 207 LAN. 209 o The advertisement is through PIM Hello message. 211 Except for the information recorded in section 4.3.2 in [RFC7761], 212 the DR/BDR OptionValue from the neighbor is also recorded: 214 o neighbor.dr: The DR Address OptionValue that presents in the Hello 215 message from the PIM neighbor. 217 o neighbor.bdr: The BDR Address OptionValue that presents in the 218 Hello message from the PIM neighbor. 220 The pseudocode is shown below: A BDR election function is added, and 221 the DR function is updated. The validneighbor function means that a 222 valid Hello message has been received from this neighbor. 224 BDR(I) { 225 bdr = NULL 226 for each neighbor on interface I { 227 if ( neighbor.bdr != NULL ) { 228 if (validneighbor (neighbor.bdr) == TRUE) { 229 if bdr == NULL 230 bdr = neighbor.bdr 231 else (dr_is_better( neighbor.bdr, bdr, I ) == TRUE ) { 232 bdr = neighbor.bdr 233 } 234 } 235 } 236 } 237 return bdr 238 } 240 DR(I) { 241 dr = NULL 242 for each neighbor on interface I { 243 if ( neighbor.dr != NULL ) { 244 if (validneighbor (neighbor.dr) == TRUE) { 245 if (dr == NULL) 246 dr = neighbor.dr 247 else (dr_is_better( neighbor.dr, dr, I ) == TRUE ) { 248 dr = neighbor.dr 249 } 250 } 251 } 252 } 253 if (dr == NULL) { 254 dr = bdr 255 } 256 if (dr == NULL) { 257 dr = me 258 } 259 return dr 260 } 262 Compare to the DR election function defined in section 4.3.2 in 263 [RFC7761] the differences include: 265 o The router, that can be elected as DR, has the highest priority 266 among the DR candidates. The elected DR may not be the one that 267 has the highest priority in the LAN. 269 o The router that supports the election algorithm defined in section 270 3.1 MUST advertise the DR Address option defined in section 4.1 in 271 PIM Hello message, and SHOULD advertise the BDR Address option 272 defined in section 4.2 in PIM Hello message. In case a DR is 273 elected and no BDR is elected, only the DR Address option is 274 advertised in the LAN. 276 3.2. Sending Hello Messages 278 When PIM is enabled on an interface or a router first starts, Hello 279 messages MUST be sent with the OptionValue of the DR Address option 280 set to 0x0. The BDR Address option SHOULD also be sent, the 281 OptionValue MUST be set to 0x0. Then the interface starts a timer 282 which value is set to Default_Hello_Holdtime. When the timer 283 expires, the DR and BDR will be elected on the interface according to 284 the DR election algorithm (Section 3.1). 286 After the election, if there is one existed DR in the LAN, the DR 287 remains unchanged. If there is no existed DR in the LAN, a new DR is 288 elected, the routers in the LAN MUST send the Hello message with the 289 OptionValue of DR Address option set to the elected DR. If there are 290 more than one routers with non-zero DR priority in the LAN, a BDR is 291 also elected. Then the routers in the LAN MUST send the Hello 292 message with the OptionValue of BDR Address option set to the elected 293 BDR. Any DROther router MUST NOT use its IP addresses in the DR/BDR 294 Address option. 296 DR newcomer 297 \ / 298 ----- ----- ----- 299 | A | | B | | C | 300 ----- ----- ----- 301 | | | 302 | | | 303 ------------------------------------------- LAN 304 Figure 2 306 For example, there is a stable LAN that includes RouterA and RouterB. 307 RouterA is the DR that has the highest priority. RouterC is a 308 newcomer. RouterC sends a Hello message with the OptionValue of DR/ 309 BDR Address option set to zero. RouterA and RouterB sends the Hello 310 message with the DR OptionValue set to RouterA, the BDR OptionValue 311 set to RouterB. 313 In case RouterC has a higher priority than RouterB, RouterC elects 314 itself as the BDR after it runs the election algorithm, then RouterC 315 sends Hello messages with the DR OptionValue set to the IP address of 316 current DR (RouterA), and the BDR OptionValue set to RouterC. 318 In case RouterB has a higher priority than RouterC, RouterC finds 319 that it can not be the BDR after it runs the election algorithm, it 320 sets the status to DROther. Then RouterC sends Hello messages with 321 the DR OptionValue set to RouterA and the BDR OptionValue set to 322 RouterB. 324 3.3. Receiving Hello Messages 326 When a Hello message is received, the OptionValue of DR/BDR is 327 checked. If the OptionValue of DR is not zero and it isn't the same 328 with local stored values, or the OptionValue of DR is zero but the 329 advertising router is the stored DR, the interface timer of election 330 MAY be set/reset. 332 Before the election algorithm runs, the validity check MUST be done. 333 The DR/BDR OptionValue in the Hello message MUST match with a known 334 neighbor, otherwise the DR/BDR OptionValue can not become the DR/BDR 335 candidates. 337 If there is one or more candidates which are different from the 338 stored DR/BDR value after the validity check, the election MUST be 339 taken. The new DR/BDR will be elected according to the rules defined 340 in section 3.1. 342 3.4. Working with the DRLB function 344 A network can use the enhancement described in this document with the 345 DR Load Balancing (DRLB) mechanism [RFC8775]. The DR MUST send the 346 DRLB-List Hello Option defined in [RFC8775]. If the DR becomes 347 unreachable, the BDR will take over all the multicast flows on the 348 link, which may result in duplicated traffic as it may not have been 349 a Group DR (GDR). The new DR MUST then follow the procedures in 350 [RFC8775]. 352 In case the DR, or the BDR which becomes DR after the DR failure, 353 doesn't support the mechanism defined in [RFC8775], the DRLB-List 354 Hello Option can not be advertised, then the DRLB mechanism takes no 355 effection. 357 4. PIM Hello message format 359 Two new PIM Hello Options are defined, which conform to the format 360 defined in [RFC7761]. 362 0 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 | OptionType | OptionLength | 366 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 367 | OptionValue | 368 | ... | 369 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 370 Figure 3: Hello Option Format 372 4.1. DR Address Option format 374 0 1 2 3 375 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 1 376 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 377 | Type = 37 | Length = | 378 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 379 | DR Address (Encoded-Unicast format) | 380 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 381 Figure 4: DR Address Option 383 o OptionType : The value is 37. 385 o OptionLength: 4 bytes if using IPv4 and 16 bytes if using IPv6. 387 o DR Address: If the IP version of the PIM message is IPv4, the 388 value MUST be the IPv4 address of the DR. If the IP version of 389 the PIM message is IPv6, the value MUST be the link-local address 390 of the DR. 392 4.2. BDR Address Option format 394 0 1 2 3 395 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 1 396 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 397 | Type = 38 | Length = | 398 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 399 | BDR Address (Encoded-Unicast format) | 400 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 401 Figure 5: BDR Address Option 403 o OptionType : The value is 38. 405 o OptionLength: 4 bytes if using IPv4 and 16 bytes if using IPv6. 407 o BDR Address: If the IP version of the PIM message is IPv4, the 408 value MUST be the IPv4 address of the BDR. If the IP version of 409 the PIM message is IPv6, the value MUST be the link-local address 410 of the BDR. 412 4.3. Error handling 414 The DR and BDR addresses MUST correspond to an address used to send 415 PIM Hello messages by one of the PIM neighbors on the interface. If 416 that is not the case then the OptionValue of DR/BDR MUST be ignored 417 as described in section 3.3. 419 An option with unexpected values MUST be ignored. For example, a DR 420 Address option with an IPv4 address received while the interface only 421 supports IPv6 is ignored. 423 5. Backwards Compatibility 425 Any router using the DR and BDR Address Options MUST set the 426 corresponding OptionValues. If at least one router on a LAN doesn't 427 send a Hello message, including the DR Address Option, then the 428 specification in this document MUST NOT be used. For example, the 429 routers in a LAN all support the options defined in this document, 430 the DR/BDR is elected. A new router which doesn't support the 431 options joins, when the hello message without DR Address Option is 432 received, all the router MUST switch the election function back 433 immediately. This action results in all routers using the DR 434 election function defined in [RFC7761] or [I-D.mankamana-pim-bdr]. 435 Both this draft and the draft [I-D.mankamana-pim-bdr], introduce a 436 backup DR. The later draft does this without introducing new options 437 but does not consider the sticky behavior. In case there is router 438 which doesn't support the DR/BDR Address Option defined in this 439 document, the routers SHOULD take the function defined in 440 [I-D.mankamana-pim-bdr] if all the routers support it, otherwise the 441 router SHOULD used the function defined in [RFC7761]. 443 A router that does not support this specification ignores unknown 444 options according to section 4.9.2 defined in [RFC7761]. So the new 445 extension defined in this draft will not influence the stability of 446 neighbors. 448 6. Security Considerations 450 [RFC7761] describes the security concerns related to PIM-SM. A rogue 451 router can become the DR/BDR by appropriately crafting the Address 452 options to include a more desirable IP address or priority. Because 453 the election algorithm makes the DR role be non-preemptive, an 454 attacker can then take control for long periods of time. The effect 455 of these actions can result in multicast flows not being forwarded 456 (already considered in [RFC7761]). 458 Some security measures, such as IP address filtering for the 459 election, may be taken to avoid these situations. For example, the 460 Hello message received from an untrusted neighbor is ignored by the 461 election process. 463 7. IANA Considerations 465 IANA is requested to allocate two new code points from the "PIM-Hello 466 Options" registry. 468 +------+--------------------+---------------+ 469 | Type | Description | Reference | 470 +------+--------------------+---------------+ 471 | 37 | DR Address Option | This Document | 472 | 38 | BDR Address Option | This Document | 473 +------+--------------------+---------------+ 475 Table 1 477 8. Acknowledgements 479 The authors would like to thank Alvaro Retana, Greg Mirsky, Jake 480 Holland, Stig Venaas for their valuable comments and suggestions. 482 9. References 484 9.1. Normative References 486 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 487 Requirement Levels", BCP 14, RFC 2119, 488 DOI 10.17487/RFC2119, March 1997, 489 . 491 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 492 DOI 10.17487/RFC2328, April 1998, 493 . 495 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 496 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 497 Multicast - Sparse Mode (PIM-SM): Protocol Specification 498 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 499 2016, . 501 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 502 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 503 May 2017, . 505 [RFC8775] Cai, Y., Ou, H., Vallepalli, S., Mishra, M., Venaas, S., 506 and A. Green, "PIM Designated Router Load Balancing", 507 RFC 8775, DOI 10.17487/RFC8775, April 2020, 508 . 510 9.2. Informative References 512 [I-D.ietf-pim-bfd-p2mp-use-case] 513 Mirsky, G. and J. Xiaoli, "Bidirectional Forwarding 514 Detection (BFD) for Multi-point Networks and Protocol 515 Independent Multicast - Sparse Mode (PIM-SM) Use Case", 516 draft-ietf-pim-bfd-p2mp-use-case-05 (work in progress), 517 November 2020. 519 [I-D.mankamana-pim-bdr] 520 mishra, m., Goh, J., and G. Mishra, "PIM Backup Designated 521 Router Procedure", draft-mankamana-pim-bdr-04 (work in 522 progress), April 2020. 524 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 525 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 526 . 528 Authors' Addresses 530 Zheng(Sandy) Zhang 531 ZTE Corporation 532 No. 50 Software Ave, Yuhuatai Distinct 533 Nanjing 534 China 536 Email: zhang.zheng@zte.com.cn 538 Fangwei Hu 539 Individual 540 Shanghai 541 China 543 Email: hufwei@gmail.com 544 Benchong Xu 545 ZTE Corporation 546 No. 68 Zijinghua Road, Yuhuatai Distinct 547 Nanjing 548 China 550 Email: xu.benchong@zte.com.cn 552 Mankamana Mishra 553 Cisco Systems 554 821 Alder Drive, 555 MILPITAS, CALIFORNIA 95035 556 UNITED STATES 558 Email: mankamis@cisco.com