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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MULTIMOB Working Group H. Asaeda 3 Internet-Draft Keio University 4 Expires: November 28, 2011 H. Liu 5 Q. Wu 6 Huawei Technologies 7 May 27, 2011 9 Tuning the Behavior of IGMP and MLD for Mobile Hosts and Routers 10 draft-ietf-multimob-igmp-mld-tuning-00 12 Abstract 14 IGMP and MLD are the protocols used by hosts to report their IP 15 multicast group memberships to neighboring multicast routers. This 16 document describes the ways of IGMPv3 and MLDv2 protocol optimization 17 for mobility, and aims to become a guideline for query and other 18 timers tuning. 20 Status of this Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at http://datatracker.ietf.org/drafts/current/. 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 This Internet-Draft will expire on November 28, 2011. 37 Copyright Notice 39 Copyright (c) 2011 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 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 This document may contain material from IETF Documents or IETF 53 Contributions published or made publicly available before November 54 10, 2008. The person(s) controlling the copyright in some of this 55 material may not have granted the IETF Trust the right to allow 56 modifications of such material outside the IETF Standards Process. 57 Without obtaining an adequate license from the person(s) controlling 58 the copyright in such materials, this document may not be modified 59 outside the IETF Standards Process, and derivative works of it may 60 not be created outside the IETF Standards Process, except to format 61 it for publication as an RFC or to translate it into languages other 62 than English. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 67 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 68 3. Explicit Tracking of Membership Status . . . . . . . . . . . . 5 69 4. Tuning IGMP/MLD Timers and Values . . . . . . . . . . . . . . 6 70 4.1. Tuning IGMP/MLD General Query Interval . . . . . . . . . . 6 71 4.2. Tuning IGMP/MLD Query Response Interval . . . . . . . . . 6 72 4.3. Tuning Last Member Query Timer (LMQT) and Last 73 Listener Query Timer (LLQT) . . . . . . . . . . . . . . . 7 74 4.4. Tuning Startup Query Interval . . . . . . . . . . . . . . 8 75 4.5. Tuning Robustness Variable . . . . . . . . . . . . . . . . 8 76 5. Destination Address of Specific Query . . . . . . . . . . . . 9 77 6. Interoperability . . . . . . . . . . . . . . . . . . . . . . . 10 78 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11 79 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 80 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 81 9.1. Normative References . . . . . . . . . . . . . . . . . . . 13 82 9.2. Informative References . . . . . . . . . . . . . . . . . . 13 83 Appendix A. Unicasting General Query . . . . . . . . . . . . . . 14 84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 86 1. Introduction 88 The Internet Group Management Protocol (IGMP) [2] for IPv4 and the 89 Multicast Listener Discovery Protocol (MLD) [3] for IPv6 are the 90 standard protocols for hosts to initiate joining or leaving multicast 91 sessions. These protocols must be also supported by multicast 92 routers or IGMP/MLD proxies [10] that maintain multicast membership 93 information on their downstream interfaces. Conceptually, IGMP and 94 MLD work on wireless networks. However, wireless access technologies 95 operate on a shared medium or a point-to-point link with limited 96 frequency and bandwidth. In many wireless regimes, it is desirable 97 to minimize multicast-related signaling to preserve the limited 98 resources of battery powered mobile devices and the constrained 99 transmission capacities of the networks. A mobile host may cause 100 initiation and termination of a multicast service in the new or the 101 previous network upon its movement. Slow multicast service 102 activation following a join may degrade reception quality. Slow 103 service termination triggered by IGMP/MLD querying or by a rapid 104 departure of the mobile host without leaving the group in the 105 previous network may waste network resources. 107 To create the optimal multicast membership management condition, IGMP 108 and MLD protocols could be tuned to "ease a mobile host's processing 109 cost or battery power consumption by IGMP/MLD Query transmission 110 timing coordination by routers" and "realize fast state convergence 111 by successive monitoring whether downstream members exist or not". 113 This document describes the ways of tuning the IGMPv3 and MLDv2 114 protocol behavior for mobility, including query and other timers 115 tuning. The selective optimization that provides tangible benefits 116 to the mobile hosts and routers is given by keeping track of 117 downstream hosts' membership status and varying IGMP/MLD Query types 118 and values to tune the number of responses. The proposed behavior 119 interoperates with the IGMPv3 and MLDv2 protocols. 121 2. Terminology 123 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL 124 NOT","SHOULD", "SHOULD NOT", "RECOMMENDED","MAY", and "OPTIONAL" in 125 this document are to be interpreted as described in RFC 2119 [1]. 127 3. Explicit Tracking of Membership Status 129 Mobile hosts use IGMP and MLD to request to join or leave multicast 130 sessions. When the adjacent upstream routers receive the IGMP/MLD 131 Report messages, they recognize the membership status on the link. 132 To update the membership status, the routers send IGMP/MLD Query 133 messages periodically as a soft-state approach does, and the member 134 hosts reply IGMP/MLD Report messages upon reception. IGMP/MLD Query 135 is therefore necessary to obtain the up-to-date membership 136 information, but a large number of the reply messages sent from all 137 member hosts may cause network congestion or consume network 138 bandwidth. 140 The "explicit tracking function" [9] is the possible approach to 141 reduce the transmitted number of IGMP/MLD messages and contribute to 142 mobile communications. It enables the router to keep track of the 143 membership status of the downstream IGMPv3 or MLDv2 member hosts. 145 The explicit tracking function reduces the chance of Group-Specific 146 or Group-and-Source Specific Query transmission. Whenever a router 147 that does not enable the explicit tracking function receives the 148 State-Change Report and the router's membership state is changed to 149 block some source or group, it sends the corresponding Group-Specific 150 or Group-and-Source Specific Query messages to confirm whether the 151 Report sender is the last member host or not. However, if a router 152 enables the explicit tracking function, it does not always need to 153 ask Current-State Report message transmission to the receiver hosts 154 since the router recognizes the (potential) last member host when it 155 receives the State-Change Report. The router can therefore send 156 IGMP/MLD Group-Specific and Group-and-Source Specific Queries LMQC/ 157 LLQC times (see Section 4.3 for LMQC/LLQC) only when it recognizes 158 the last member has left from the network. This reduces the 159 transmitted number of Current-State Report messages. 161 Enabling the explicit tracking function is advantageous for mobile 162 multicast, but the function requires additional processing capability 163 and a possibly large memory for routers to keep all membership 164 status. Especially when a router needs to maintain a large number of 165 receiver hosts, this resource requirement may be potentially- 166 impacted. Therefore, in this document, we propose that adjacent 167 upstream multicast routers SHOULD enable the explicit tracking 168 function for IP multicast communications on wireless networks, if 169 they have enough resources. If operators think that their routers do 170 not have enough resources, they MAY decide to disable this function 171 on their routers. Note that whether routers enable the explicit 172 tracking function or not, they need to maintain downstream membership 173 status by sending IGMPv3/MLDv2 General Query messages as some IGMPv3/ 174 MLDv2 messages may be lost during transmission. 176 4. Tuning IGMP/MLD Timers and Values 178 4.1. Tuning IGMP/MLD General Query Interval 180 IGMP and MLD are non-reliable protocols; to cover the possibility of 181 a State-Change Report being missed by one or more multicast routers, 182 "hosts retransmit the same State-Change Report messages [Robustness 183 Variable] - 1 more times", at intervals chosen at random from the 184 range (0, [Unsolicited Report Interval]) [2][3]. Although this 185 behavior increases the protocol robustness, it does not guarantee 186 that the State-Change Report is reached to the routers. Therefore, 187 routers still need to refresh the downstream membership information 188 by receiving Current-State Report periodically solicited by IGMP/MLD 189 General Query sent in the [Query Interval] period, in order to be 190 robust in front of host or link failures and packet loss. It also 191 supports the situation that mobile hosts turn off or move from the 192 wireless network to other wireless network managed by the different 193 router without any notification (e.g., leave request). 195 The [Query Interval] is the interval between General Queries sent by 196 the regular IGMPv3/MLDv2 querier, and the default value is 125 197 seconds [2][3]. By varying the [Query Interval], multicast routers 198 can tune the number of IGMP/MLD messages on the network; larger 199 values cause IGMP/MLD Queries to be sent less often. 201 This document proposes 150 seconds for the [Query Interval] value by 202 changing the Querier's Query Interval Code (QQIC) field specified in 203 the IGMP/MLD Query message, for the case that a router enabling the 204 explicit tracking function sends General Query and potentially 205 operates a large number of member hosts such as more than 200 hosts 206 on the wireless link. This longer interval value contributes to 207 minimizing traffic of Report messages and battery power consumption 208 for mobile hosts. 210 On the other hand, this document also proposes 60 to 90 seconds for 211 the [Query Interval] value for the case that a router enabling the 212 explicit tracking function attaches to a wireless link having higher 213 capacity of the resource. This shorter interval contributes to quick 214 synchronization of the membership information tracked by the router 215 but may consume battery power of mobile hosts. 217 If a router does not enable the explicit tracking function, the 218 [Query Interval] value would be its default value, 125 seconds. 220 4.2. Tuning IGMP/MLD Query Response Interval 222 The [Query Response Interval] is the Max Response Time (or Max 223 Response Delay) used to calculate the Max Resp Code inserted into the 224 periodic General Queries. Its default value is 10 seconds expressed 225 by "Max Resp Code=100" for IGMPv3 [2] and "Maximum Response 226 Code=10000" for MLDv2 [3]. By varying the [Query Response Interval], 227 multicast routers can tune the burstiness of IGMP/MLD messages on the 228 network; larger values make the traffic less bursty as host responses 229 are spread out over a larger interval, but will increase join latency 230 when State-Change Report is missing. 232 According to our experimental analysis, this document proposes two 233 tuning scenarios for tuning the [Query Response Interval] value in 234 different wireless link conditions; one scenario is for a wireless 235 link with a lower capacity of network resource or a lossy link, and 236 the other scenario is for a wireless link with enough capacity or 237 reliable condition for IGMP/MLD message transmission. 239 Regarding the first scenario, for instance, when a multicast router 240 attaches to a bursty IEEE 802.11b link, the router configures the 241 longer [Query Response Interval] value, such as 10 to 20 (sec). This 242 configuration will reduce congestion of the Current-State Report 243 messages on a link but may increase join latency and leave latency 244 when the unsolicited messages (State-Change Record) are lost on the 245 router. 247 The second scenario may happen for a multicast router attaching to a 248 wireless link having higher capacity of the resource or a point-to- 249 (multi-)point link such as an IEEE 802.16e link, because IGMP/MLD 250 messages do not seriously affect the link condition. The router can 251 seek Current-State Report messages with the shorter [Query Response 252 Interval] value, such as 5 to 10 (sec). This configuration will 253 contribute to quickly (at some level) discovering non-tracked member 254 hosts and synchronizing the membership information. 256 4.3. Tuning Last Member Query Timer (LMQT) and Last Listener Query 257 Timer (LLQT) 259 Shortening the Last Member Query Timer (LMQT) for IGMPv3 and the Last 260 Listener Query Timer (LLQT) for MLDv2 contributes to minimizing leave 261 latency. LMQT is represented by the Last Member Query Interval 262 (LMQI), multiplied by the Last Member Query Count (LMQC), and LLQT is 263 represented by the Last Listener Query Interval (LLQI), multiplied by 264 the Last Listener Query Count (LLQC). 266 While LMQI and LLQI are changeable, it is reasonable to use the 267 default values (i.e., 1 second) for LMQI and LLQI in a wireless 268 network. LMQC and LLQC, whose default value is the [Robustness 269 Variable] value, are also tunable. Therefore, LMQC and LLQC MAY be 270 set to "1" for routers enabling the explicit tracking function, and 271 then LMQT and LLQT are set to 1 second. However, setting LMQC and 272 LLQC to 1 increases the risk of missing the last member; LMQC and 273 LLQC SHOULD be set to 1 only when network operators think that their 274 wireless link is stable enough. 276 On the other hand, if network operators think that their wireless 277 link is lossy (e.g., due to a large number of attached hosts or 278 limited resources), they MAY set LMQC and LLQC to "2" for their 279 routers enabling the explicit tracking function. Although bigger 280 LMQC and LLQC values may cause longer leave latency, the risk of 281 missing the last member will be reduced. 283 4.4. Tuning Startup Query Interval 285 The [Startup Query Interval] is the interval between General Queries 286 sent by a Querier on startup. The default value is 1/4 of [Query 287 Interval]; however, this document recommends the use of its shortened 288 value such as 1 second since the shorter value would contribute to 289 smooth handover for mobile hosts using, e.g., PMIPv6 [11]. Note that 290 the [Startup Query Interval] is a static value and cannot be changed 291 by any external signal. Therefore operators who maintain routers and 292 wireless links must properly configure this value. 294 4.5. Tuning Robustness Variable 296 To cover the possibility of unsolicited reports being missed by 297 multicast routers, unsolicited reports are retransmitted [Robustness 298 Variable] - 1 more times, at intervals chosen at random from the 299 defined range [2][3]. The QRV (Querier's Robustness Variable) field 300 in IGMP/MLD Query contains the [Robustness Variable] value used by 301 the querier. The default [Robustness Variable] value defined in 302 IGMPv3 [2] and MLDv2 [3] is "2". 304 This document proposes "2" for the [Robustness Variable] value for 305 mobility, when a router attaches to a wireless link having lower 306 capacity of the resource or a large number of hosts. For a router 307 that attaches to a wireless link having higher capacity of the 308 resource or reliable condition, it is not required to retransmit the 309 same State-Change Report message; hence the router sets the 310 [Robustness Variable] to "1". Note that whether the explicit 311 tracking function is enabled or not, the [Robustness Variable] value 312 SHOULD NOT be bigger than "2". 314 5. Destination Address of Specific Query 316 IGMP/MLD Group-Specific and Group-and-Source Specific Queries defined 317 in [2][3] are sent to verify whether there are hosts that desire 318 reception of the specified group or a set of sources or to rebuild 319 the desired reception state for a particular group or a set of 320 sources. These specific Queries build and refresh multicast 321 membership state of hosts on an attached network. These specific 322 Queries should be sent to each desired hosts with specific multicast 323 address (not the all-hosts/all-nodes multicast address) as their IP 324 destination addresses, because hosts that do not join the multicast 325 session do not pay attention to these specific Queries, and only 326 active member hosts that have been receiving multicast contents with 327 the specified address reply IGMP/MLD reports. 329 6. Interoperability 331 IGMPv3 [2] and MLDv2 [3] provide the ability for hosts to report 332 source-specific subscriptions. With IGMPv3/MLDv2, a mobile host can 333 specify a channel of interest, using multicast group and source 334 addresses in its join request. Upon its reception, the upstream 335 router that supports IGMPv3/MLDv2 establishes the shortest path tree 336 toward the source without coordinating a shared tree. This function 337 is called the source filtering function and required to support 338 Source-Specific Multicast (SSM) [8]. 340 Recently, the Lightweight-IGMPv3 (LW-IGMPv3) and Lightweight-MLDv2 341 (LW-MLDv2) [4] protocols have been proposed in the IETF. These 342 protocols provide protocol simplicity for mobile hosts and routers, 343 as they eliminate a complex state machine from the full versions of 344 IGMPv3 and MLDv2, and promote the opportunity to implement SSM in 345 mobile communications. 347 This document assumes that both multicast routers and mobile hosts 348 MUST be IGMPv3/MLDv2 capable, regardless whether the protocols are 349 the full or lightweight version. And this document does not consider 350 interoperability with older version protocols. The main reason not 351 being interoperate with older IGMP/MLD protocols is that the explicit 352 tracking function does not work properly with older IGMP/MLD 353 protocols. 355 7. Security Considerations 357 This document neither provides new functions or modifies the standard 358 functions defined in [2][3][4]. Therefore there is no additional 359 security consideration provided. 361 8. Acknowledgements 363 Marshall Eubanks, Gorry Fairhurst, Behcet Sarikaya, Yogo Uchida, Stig 364 Venaas, Jinwei Xia, and others provided many constructive and 365 insightful comments. 367 9. References 369 9.1. Normative References 371 [1] Bradner, S., "Key words for use in RFCs to indicate requirement 372 levels", RFC 2119, March 1997. 374 [2] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. 375 Thyagarajan, "Internet Group Management Protocol, Version 3", 376 RFC 3376, October 2002. 378 [3] Vida, R. and L. Costa, "Multicast Listener Discovery Version 2 379 (MLDv2) for IPv6", RFC 3810, June 2004. 381 [4] Liu, H., Cao, W., and H. Asaeda, "Lightweight IGMPv3 and MLDv2 382 Protocols", RFC 5790, February 2010. 384 [5] Deering, S., "Host Extensions for IP Multicasting", RFC 1112, 385 August 1989. 387 [6] Fenner, W., "Internet Group Management Protocol, Version 2", 388 RFC 2236, July 1997. 390 [7] Deering, S., Fenner, W., and B. Haberman, "Multicast Listener 391 Discovery (MLD) for IPv6", RFC 2710, October 1999. 393 [8] Holbrook, H. and B. Cain, "Source-Specific Multicast for IP", 394 RFC 4607, August 2006. 396 [9] Asaeda, H. and Y. Uchida, "IGMP/MLD-Based Explicit Membership 397 Tracking Function for Multicast Routers", 398 draft-asaeda-mboned-explicit-tracking-01.txt (work in 399 progress), October 2010. 401 9.2. Informative References 403 [10] Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet 404 Group Management Protocol (IGMP) / Multicast Listener Discovery 405 (MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")", 406 RFC 4605, August 2006. 408 [11] Gundavelli, S, Ed., Leung, K., Devarapalli, V., Chowdhury, K., 409 and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008. 411 Appendix A. Unicasting General Query 413 IGMPv3 and MLDv2 specifications [2][3] describe that a host MUST 414 accept and process any Query whose IP Destination Address field 415 contains any of the addresses (unicast or multicast) assigned to the 416 interface on which the Query arrives. In general, the all-hosts 417 multicast address (224.0.0.1) or link-scope all-nodes multicast 418 address (FF02::1) is used as the IP destination address of IGMP/MLD 419 General Query. On the other hand, according to [2][3], a router MAY 420 be able to unicast General Query to tracked member hosts in [Query 421 Interval], if the router keeps track of membership information 422 (Section 3). 424 Unicasting IGMP/MLD General Query would reduce the drain on battery 425 power of mobile hosts as only the active hosts that have been 426 receiving multicast contents respond the unicast IGMP/MLD General 427 Query messages and non-active hosts do not need to pay attention to 428 the IGMP/MLD messages. This also allows the upstream router to 429 proceed fast leaves (or shorten leave latency) by setting LMQC/LLQC 430 smaller, because the router can immediately converge and update the 431 membership information, ideally. 433 However, there is a concern in unicast General Query. If a multicast 434 router sends General Query "only" by unicast, it cannot discover 435 potential member hosts whose join requests were lost. Since the 436 hosts do not retransmit the same join requests (i.e., unsolicited 437 Report messages), they loose the chance to join the channels unless 438 the upstream router asks the membership information by sending 439 General Query by multicast. It will be solved by using both unicast 440 and multicast General Queries and configuring the [Query Interval] 441 timer value for multicast General Query and the [Unicast Query 442 Interval] timer value for unicast General Query. However, using two 443 different timers for General Queries would require the protocol 444 extension this document does not focus on. If a router does not 445 distinguish the multicast and unicast General Query Intervals, the 446 router should only use and enable multicast General Query. 448 Also, unicasting General Query does not remove multicasting General 449 Query. Multicast General Query is necessary to update membership 450 information if it is not correctly synchronized due to missing 451 Reports. Therefore, enabling unicast General Query SHOULD NOT be 452 used for the implementation that does not allow to configure 453 different query interval timers as [Query Interval] and [Unicast 454 Query Interval] (See Appendix A for the detail). If a router does 455 not distinguish these multicast and unicast General Query Intervals, 456 the router SHOULD only use and enable multicast General Query. 458 Authors' Addresses 460 Hitoshi Asaeda 461 Keio University 462 Graduate School of Media and Governance 463 5322 Endo 464 Fujisawa, Kanagawa 252-0882 465 Japan 467 Email: asaeda@wide.ad.jp 468 URI: http://www.sfc.wide.ad.jp/~asaeda/ 470 Hui Liu 471 Huawei Technologies Co., Ltd. 472 Huawei Bld., No.3 Xinxi Rd. 473 Shang-Di Information Industry Base 474 Hai-Dian Distinct, Beijing 100085 475 China 477 Email: helen.liu@huawei.com 479 Qin Wu 480 Huawei Technologies Co., Ltd. 481 Site B, Floor 12F, Huihong Mansion 482 No.91 Baixia Rd. 483 Nanjing, Jiangsu 21001 484 China 486 Email: Sunseawq@huawei.com