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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Missing Reference: 'ICMPv6' is mentioned on line 592, but not defined -- Looks like a reference, but probably isn't: '1' on line 1136 == Unused Reference: 'RFC5796' is defined on line 1071, but no explicit reference was found in the text == Outdated reference: A later version (-30) exists of draft-ietf-6tisch-architecture-29 -- Obsolete informational reference (is this intentional?): RFC 2461 (Obsoleted by RFC 4861) -- Obsolete informational reference (is this intentional?): RFC 4601 (Obsoleted by RFC 7761) Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Area C. Perkins 3 Internet-Draft Blue Meadow Networks 4 Intended status: Informational M. McBride 5 Expires: April 29, 2021 Futurewei 6 D. Stanley 7 HPE 8 W. Kumari 9 Google 10 JC. Zuniga 11 SIGFOX 12 October 26, 2020 14 Multicast Considerations over IEEE 802 Wireless Media 15 draft-ietf-mboned-ieee802-mcast-problems-12 17 Abstract 19 Well-known issues with multicast have prevented the deployment of 20 multicast in 802.11 (wifi) and other local-area wireless 21 environments. This document describes the problems of known 22 limitations with wireless (primarily 802.11) Layer-2 multicast. Also 23 described are certain multicast enhancement features that have been 24 specified by the IETF, and by IEEE 802, for wireless media, as well 25 as some operational choices that can be taken to improve the 26 performance of the network. Finally, some recommendations are 27 provided about the usage and combination of these features and 28 operational choices. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at https://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on April 29, 2021. 47 Copyright Notice 49 Copyright (c) 2020 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (https://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 65 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 66 3. Identified multicast issues . . . . . . . . . . . . . . . . . 5 67 3.1. Issues at Layer 2 and Below . . . . . . . . . . . . . . . 5 68 3.1.1. Multicast reliability . . . . . . . . . . . . . . . . 6 69 3.1.2. Lower and Variable Data Rate . . . . . . . . . . . . 6 70 3.1.3. Capacity and Impact on Interference . . . . . . . . . 7 71 3.1.4. Power-save Effects on Multicast . . . . . . . . . . . 7 72 3.2. Issues at Layer 3 and Above . . . . . . . . . . . . . . . 8 73 3.2.1. IPv4 issues . . . . . . . . . . . . . . . . . . . . . 8 74 3.2.2. IPv6 issues . . . . . . . . . . . . . . . . . . . . . 8 75 3.2.3. MLD issues . . . . . . . . . . . . . . . . . . . . . 9 76 3.2.4. Spurious Neighbor Discovery . . . . . . . . . . . . . 9 77 4. Multicast protocol optimizations . . . . . . . . . . . . . . 10 78 4.1. Proxy ARP in 802.11-2012 . . . . . . . . . . . . . . . . 10 79 4.2. IPv6 Address Registration and Proxy Neighbor Discovery . 11 80 4.3. Buffering to Improve Battery Life . . . . . . . . . . . . 12 81 4.4. Limiting multicast buffer hardware queue depth . . . . . 13 82 4.5. IPv6 support in 802.11-2012 . . . . . . . . . . . . . . . 13 83 4.6. Using Unicast Instead of Multicast . . . . . . . . . . . 14 84 4.6.1. Overview . . . . . . . . . . . . . . . . . . . . . . 14 85 4.6.2. Layer 2 Conversion to Unicast . . . . . . . . . . . . 14 86 4.6.3. Directed Multicast Service (DMS) . . . . . . . . . . 14 87 4.6.4. Automatic Multicast Tunneling (AMT) . . . . . . . . . 15 88 4.7. GroupCast with Retries (GCR) . . . . . . . . . . . . . . 15 89 5. Operational optimizations . . . . . . . . . . . . . . . . . . 16 90 5.1. Mitigating Problems from Spurious Neighbor Discovery . . 16 91 5.2. Mitigating Spurious Service Discovery Messages . . . . . 18 92 6. Multicast Considerations for Other Wireless Media . . . . . . 18 93 7. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 19 94 8. On-going Discussion Items . . . . . . . . . . . . . . . . . . 19 95 9. Security Considerations . . . . . . . . . . . . . . . . . . . 20 96 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 97 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20 98 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 99 12.1. Informative References . . . . . . . . . . . . . . . . . 20 100 12.2. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 25 101 Appendix A. Changes in this draft between revisions 06 versus 07 25 102 Appendix B. Changes in this draft between revisions 05 versus 06 25 103 Appendix C. Changes in this draft between revisions 04 versus 05 25 104 Appendix D. Changes in this draft between revisions 03 versus 04 26 105 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26 107 1. Introduction 109 Well-known issues with multicast have prevented the deployment of 110 multicast in 802.11 [dot11] and other local-area wireless 111 environments, as described in [mc-props], [mc-prob-stmt]. 112 Performance issues have been observed when multicast packet 113 transmissions of IETF protocols are used over IEEE 802 wireless 114 media. Even though enhancements for multicast transmissions have 115 been designed at both IETF and IEEE 802, incompatibilities still 116 exist between specifications, implementations and configuration 117 choices. 119 Many IETF protocols depend on multicast/broadcast for delivery of 120 control messages to multiple receivers. Multicast allows sending 121 data to multiple interested recipients without the source needing to 122 send duplicate data to each recipient. With broadcast traffic, data 123 is sent to every device regardless of their interest in the data. 124 Multicast is used for various purposes such as neighbor discovery, 125 network flooding, address resolution, as well minimizing media 126 occupancy for the transmission of data that is intended for multiple 127 receivers. In addition to protocol use of broadcast/multicast for 128 control messages, more applications, such as push to talk in 129 hospitals, or video in enterprises, universities, and homes, are 130 sending multicast IP to end user devices, which are increasingly 131 using Wi-Fi for their connectivity. 133 IETF protocols typically rely on network protocol layering in order 134 to reduce or eliminate any dependence of higher level protocols on 135 the specific nature of the MAC layer protocols or the physical media. 136 In the case of multicast transmissions, higher level protocols have 137 traditionally been designed as if transmitting a packet to an IP 138 address had the same cost in interference and network media access, 139 regardless of whether the destination IP address is a unicast address 140 or a multicast or broadcast address. This model was reasonable for 141 networks where the physical medium was wired, like Ethernet. 142 Unfortunately, for many wireless media, the costs to access the 143 medium can be quite different. Multicast over Wi-Fi has often been 144 plagued by such poor performance that it is disallowed. Some 145 enhancements have been designed in IETF protocols that are assumed to 146 work primarily over wireless media. However, these enhancements are 147 usually implemented in limited deployments and not widespread on most 148 wireless networks. 150 IEEE 802 wireless protocols have been designed with certain features 151 to support multicast traffic. For instance, lower modulations are 152 used to transmit multicast frames, so that these can be received by 153 all stations in the cell, regardless of the distance or path 154 attenuation from the base station or access point. However, these 155 lower modulation transmissions occupy the medium longer; they hamper 156 efficient transmission of traffic using higher order modulations to 157 nearby stations. For these and other reasons, IEEE 802 working 158 groups such as 802.11 have designed features to improve the 159 performance of multicast transmissions at Layer 2 [ietf_802-11]. In 160 addition to protocol design features, certain operational and 161 configuration enhancements can ameliorate the network performance 162 issues created by multicast traffic, as described in Section 5. 164 There seems to be general agreement that these problems will not be 165 fixed anytime soon, primarily because it's expensive to do so and due 166 to multicast being unreliable. Compared to unicast over Wi-Fi, 167 multicast is often treated as somewhat of a second class citizen, 168 even though there are many protocols using multicast. Something 169 needs to be provided in order to make them more reliable. IPv6 170 neighbor discovery saturating the Wi-Fi link is only part of the 171 problem. Wi-Fi traffic classes may help. This document is intended 172 to help make the determination about what problems should be solved 173 by the IETF and what problems should be solved by the IEEE (see 174 Section 8). 176 This document details various problems caused by multicast 177 transmission over wireless networks, including high packet error 178 rates, no acknowledgements, and low data rate. It also explains some 179 enhancements that have been designed at the IETF and IEEE 802.11 to 180 ameliorate the effects of multicast traffic. Recommendations are 181 also provided to implementors about how to use and combine these 182 enhancements. Some advice about the operational choices that can be 183 taken is also included. It is likely that this document will also be 184 considered relevant to designers of future IEEE wireless 185 specifications. 187 2. Terminology 189 This document uses the following definitions: 191 ACK 192 The 802.11 layer 2 acknowledgement 194 AP 195 IEEE 802.11 Access Point 197 basic rate 198 The slowest rate of all the connected devices, at which multicast 199 and broadcast traffic is generally transmitted 201 DTIM 202 Delivery Traffic Indication Map (DTIM): An information element 203 that advertises whether or not any associated stations have 204 buffered multicast or broadcast frames 206 MCS 207 Modulation and Coding Scheme 209 NOC 210 Network Operations Center 212 PER 213 Packet Error Rate 215 STA 216 802.11 station (e.g. handheld device) 218 TIM 219 Traffic Indication Map (TIM): An information element that 220 advertises whether or not any associated stations have buffered 221 unicast frames 223 3. Identified multicast issues 225 3.1. Issues at Layer 2 and Below 227 In this section some of the issues related to the use of multicast 228 transmissions over IEEE 802 wireless technologies are described. 230 3.1.1. Multicast reliability 232 Multicast traffic is typically much less reliable than unicast 233 traffic. Since multicast makes point-to-multipoint communications, 234 multiple acknowledgements would be needed to guarantee reception at 235 all recipients. Since there are no ACKs for multicast packets, it is 236 not possible for the Access Point (AP) to know whether or not a 237 retransmission is needed. Even in the wired Internet, this 238 characteristic often causes undesirably high error rates. This has 239 contributed to the relatively slow uptake of multicast applications 240 even though the protocols have long been available. The situation 241 for wireless links is much worse, and is quite sensitive to the 242 presence of background traffic. Consequently, there can be a high 243 packet error rate (PER) due to lack of retransmission, and because 244 the sender never backs off. It is not uncommon for there to be a 245 packet loss rate of 5% or more, which is particularly troublesome for 246 video and other environments where high data rates and high 247 reliability are required. 249 3.1.2. Lower and Variable Data Rate 251 Multicast over wired differs from multicast over wireless because 252 transmission over wired links often occurs at a fixed rate. Wi-Fi, 253 on the other hand, has a transmission rate that varies depending upon 254 the STA's proximity to the AP. The throughput of video flows, and 255 the capacity of the broader Wi-Fi network, will change and will 256 impact the ability for QoS solutions to effectively reserve bandwidth 257 and provide admission control. 259 For wireless stations associated with an Access Point, the power 260 necessary for good reception can vary from station to station. For 261 unicast, the goal is to minimize power requirements while maximizing 262 the data rate to the destination. For multicast, the goal is simply 263 to maximize the number of receivers that will correctly receive the 264 multicast packet; generally the Access Point has to use a much lower 265 data rate at a power level high enough for even the farthest station 266 to receive the packet, for example as briefly mentioned in section 2 267 of [RFC5757]. Consequently, the data rate of a video stream, for 268 instance, would be constrained by the environmental considerations of 269 the least reliable receiver associated with the Access Point. 271 Because more robust modulation and coding schemes (MCSs) have longer 272 range but also lower data rate, multicast / broadcast traffic is 273 generally transmitted at the slowest rate of all the connected 274 devices. This is also known as the basic rate. The amount of 275 additional interference depends on the specific wireless technology. 276 In fact, backward compatibility and multi-stream implementations mean 277 that the maximum unicast rates are currently up to a few Gbps, so 278 there can be more than 3 orders of magnitude difference in the 279 transmission rate between multicast / broadcast versus optimal 280 unicast forwarding. Some techiques employed to increase spectral 281 efficiency, such as spatial multiplexing in MIMO systems, are not 282 available with more than one intended receiver; it is not the case 283 that backwards compatibility is the only factor responsible for lower 284 multicast transmission rates. 286 Wired multicast also affects wireless LANs when the AP extends the 287 wired segment; in that case, multicast / broadcast frames on the 288 wired LAN side are copied to the Wireless Local Area Network (WLAN). 289 Since broadcast messages are transmitted at the most robust MCS, many 290 large frames are sent at a slow rate over the air. 292 3.1.3. Capacity and Impact on Interference 294 Transmissions at a lower rate require longer occupancy of the 295 wireless medium and thus take away from the airtime of other 296 communications and degrade the overall capacity. Furthermore, 297 transmission at higher power, as is required to reach all multicast 298 STAs associated to the AP, proportionately increases the area of 299 interference. 301 3.1.4. Power-save Effects on Multicast 303 One of the characteristics of multicast transmission is that every 304 station has to be configured to wake up to receive the multicast, 305 even though the received packet may ultimately be discarded. This 306 process can have a large effect on the power consumption by the 307 multicast receiver station. For this reason there are workarounds, 308 such as Directed Multicast Service (DMS) described in Section 4, to 309 prevent unnecessarily waking up stations. 311 Multicast can work poorly with the power-save mechanisms defined in 312 IEEE 802.11e, for the following reasons. 314 o Clients may be unable to stay in sleep mode due to multicast 315 control packets frequently waking them up. 316 o Both unicast and multicast traffic can be delayed by power-saving 317 mechanisms. 318 o A unicast packet is delayed until an STA wakes up and requests it. 319 Unicast traffic may also be delayed to improve power save, 320 efficiency and increase probability of aggregation. 321 o Multicast traffic is delayed in a wireless network if any of the 322 STAs in that network are power savers. All STAs associated to the 323 AP have to be awake at a known time to receive multicast traffic. 324 o Packets can also be discarded due to buffer limitations in the AP 325 and non-AP STA. 327 3.2. Issues at Layer 3 and Above 329 This section identifies some representative IETF protocols, and 330 describes possible negative effects due to performance degradation 331 when using multicast transmissions for control messages. Common uses 332 of multicast include: 334 o Control plane signaling 335 o Neighbor Discovery 336 o Address Resolution 337 o Service Discovery 338 o Applications (video delivery, stock data, etc.) 339 o On-demand routing 340 o Backbone construction 341 o Other L3 protocols (non-IP) 343 User Datagram Protocol (UDP) is the most common transport layer 344 protocol for multicast applications. By itself, UDP is not reliable 345 -- messages may be lost or delivered out of order. 347 3.2.1. IPv4 issues 349 The following list contains some representative discovery protocols, 350 which utlize broadcast/multicast, that are used with IPv4. 352 o ARP [RFC5424] 353 o DHCP [RFC2131] 354 o mDNS [RFC6762] 355 o uPnP [RFC6970] 357 After initial configuration, ARP (described in more detail later) and 358 DHCP occur much less commonly, but service discovery can occur at any 359 time. Some widely-deployed service discovery protocols (e.g., for 360 finding a printer) utilize mDNS (i.e., multicast) which is often the 361 first service that operators drop. Even if multicast snooping 362 [RFC4541] (which provides the benefit of conserving bandwidth on 363 those segments of the network where no node has expressed interest in 364 receiving packets addressed to the group address) is utilized, many 365 devices can register at once and cause serious network degradation. 367 3.2.2. IPv6 issues 369 IPv6 makes extensive use of multicast, including the following: 371 o DHCPv6 [RFC8415] 372 o Protocol Independent Multicast (PIM) [RFC7761] 373 o IPv6 Neighbor Discovery Protocol (NDP) [RFC4861] 374 o multicast DNS (mDNS) [RFC6762] 375 o Router Discovery [RFC4286] 377 IPv6 NDP Neighbor Solicitation (NS) messages used in Duplicate 378 Address Detection (DAD) and Address Lookup make use of Link-Scope 379 multicast. In contrast to IPv4, an IPv6 node will typically use 380 multiple addresses, and may change them often for privacy reasons. 381 This intensifies the impact of multicast messages that are associated 382 to the mobility of a node. Router advertisement (RA) messages are 383 also periodically multicasted over the Link. 385 Neighbors may be considered lost if several consecutive Neighbor 386 Discovery packets fail. 388 3.2.3. MLD issues 390 Multicast Listener Discovery (MLD) [RFC4541] is used to identify 391 members of a multicast group that are connected to the ports of a 392 switch. Forwarding multicast frames into a Wi-Fi-enabled area can 393 use such switch support for hardware forwarding state information. 394 However, since IPv6 makes heavy use of multicast, each STA with an 395 IPv6 address will require state on the switch for several and 396 possibly many multicast solicited-node addresses. Multicast 397 addresses that do not have forwarding state installed (perhaps due to 398 hardware memory limitations on the switch) cause frames to be flooded 399 on all ports of the switch. Some switch vendors do not support MLD, 400 for link-scope multicast, due to the increase it can cause in state. 402 3.2.4. Spurious Neighbor Discovery 404 On the Internet there is a "background radiation" of scanning traffic 405 (people scanning for vulnerable machines) and backscatter (responses 406 from spoofed traffic, etc). This means that routers very often 407 receive packets destined for IPv4 addresses regardless of whether 408 those IP addresses are in use. In the cases where the IP is assigned 409 to a host, the router broadcasts an ARP request, gets back an ARP 410 reply, and caches it; then traffic can be delivered to the host. 411 When the IP address is not in use, the router broadcasts one (or 412 more) ARP requests, and never gets a reply. This means that it does 413 not populate the ARP cache, and the next time there is traffic for 414 that IP address the router will rebroadcast the ARP requests. 416 The rate of these ARP requests is proportional to the size of the 417 subnets, the rate of scanning and backscatter, and how long the 418 router keeps state on non-responding ARPs. As it turns out, this 419 rate is inversely proportional to how occupied the subnet is (valid 420 ARPs end up in a cache, stopping the broadcasting; unused IPs never 421 respond, and so cause more broadcasts). Depending on the address 422 space in use, the time of day, how occupied the subnet is, and other 423 unknown factors, thousands of broadcasts per second have been 424 observed. Around 2,000 broadcasts per second have been observed at 425 the IETF NOC during face-to-face meetings. 427 With Neighbor Discovery for IPv6 [RFC2461], nodes accomplish address 428 resolution by multicasting a Neighbor Solicitation that asks the 429 target node to return its link-layer address. Neighbor Solicitation 430 messages are multicast to the solicited-node multicast address of the 431 target address. The target returns its link-layer address in a 432 unicast Neighbor Advertisement message. A single request-response 433 pair of packets is sufficient for both the initiator and the target 434 to resolve each other's link-layer addresses; the initiator includes 435 its link-layer address in the Neighbor Solicitation. 437 On a wired network, there is not a huge difference between unicast, 438 multicast and broadcast traffic. Due to hardware filtering (see, 439 e.g., [Deri-2010]), inadvertently flooded traffic (or excessive 440 ethernet multicast) on wired networks can be quite a bit less costly, 441 compared to wireless cases where sleeping devices have to wake up to 442 process packets. Wired Ethernets tend to be switched networks, 443 further reducing interference from multicast. There is effectively 444 no collision / scheduling problem except at extremely high port 445 utilizations. 447 This is not true in the wireless realm; wireless equipment is often 448 unable to send high volumes of broadcast and multicast traffic, 449 causing numerous broadcast and multicast packets to be dropped. 450 Consequently, when a host connects it is often not able to complete 451 DHCP, and IPv6 RAs get dropped, leading to users being unable to use 452 the network. 454 4. Multicast protocol optimizations 456 This section lists some optimizations that have been specified in 457 IEEE 802 and IETF that are aimed at reducing or eliminating the 458 issues discussed in Section 3. 460 4.1. Proxy ARP in 802.11-2012 462 The AP knows the MAC address and IP address for all associated STAs. 463 In this way, the AP acts as the central "manager" for all the 802.11 464 STAs in its basic service set (BSS). Proxy ARP is easy to implement 465 at the AP, and offers the following advantages: 467 o Reduced broadcast traffic (transmitted at low MCS) on the wireless 468 medium 469 o STA benefits from extended power save in sleep mode, as ARP 470 requests for STA's IP address are handled instead by the AP. 472 o ARP frames are kept off the wireless medium. 473 o No changes are needed to STA implementation. 475 Here is the specification language as described in clause 10.23.13 of 476 [dot11-proxyarp]: 478 When the AP supports Proxy ARP "[...] the AP shall maintain a 479 Hardware Address to Internet Address mapping for each associated 480 station, and shall update the mapping when the Internet Address of 481 the associated station changes. When the IPv4 address being 482 resolved in the ARP request packet is used by a non-AP STA 483 currently associated to the BSS, the proxy ARP service shall 484 respond on behalf of the non-AP STA". 486 4.2. IPv6 Address Registration and Proxy Neighbor Discovery 488 As used in this section, a Low-Power Wireless Personal Area Network 489 (6LoWPAN) denotes a low power lossy network (LLN) that supports 490 6LoWPAN Header Compression (HC) [RFC6282]. A 6TiSCH network 491 [I-D.ietf-6tisch-architecture] is an example of a 6LowPAN. In order 492 to control the use of IPv6 multicast over 6LoWPANs, the 6LoWPAN 493 Neighbor Discovery (6LoWPAN ND) [RFC6775] standard defines an address 494 registration mechanism that relies on a central registry to assess 495 address uniqueness, as a substitute to the inefficient DAD mechanism 496 found in the mainstream IPv6 Neighbor Discovery Protocol (NDP) 497 [RFC4861][RFC4862]. 499 The 6lo Working Group has specified an update [RFC8505] to RFC6775. 500 Wireless devices can register their address to a Backbone Router 501 [I-D.ietf-6lo-backbone-router], which proxies for the registered 502 addresses with the IPv6 NDP running on a high speed aggregating 503 backbone. The update also enables a proxy registration mechanism on 504 behalf of the registered node, e.g. by a 6LoWPAN router to which the 505 mobile node is attached. 507 The general idea behind the backbone router concept is that broadcast 508 and multicast messaging should be tightly controlled in a variety of 509 WLANs and Wireless Personal Area Networks (WPANs). Connectivity to a 510 particular link that provides the subnet should be left to Layer-3. 511 The model for the Backbone Router operation is represented in 512 Figure 1. 514 | 515 +-----+ 516 | | Gateway (default) router 517 | | 518 +-----+ 519 | 520 | Backbone Link 521 +--------------------+------------------+ 522 | | | 523 +-----+ +-----+ +-----+ 524 | | Backbone | | Backbone | | Backbone 525 | | router 1 | | router 2 | | router 3 526 +-----+ +-----+ +-----+ 527 o o o o o o 528 o o o o o o o o o o o o o o 529 o o o o o o o o o o o o o o o 530 o o o o o o o o o o 531 o o o o o o o 533 LLN 1 LLN 2 LLN 3 535 Figure 1: Backbone Link and Backbone Routers 537 LLN nodes can move freely from an LLN anchored at one IPv6 Backbone 538 Router to an LLN anchored at another Backbone Router on the same 539 backbone, keeping any of the IPv6 addresses they have configured. 540 The Backbone Routers maintain a Binding Table of their Registered 541 Nodes, which serves as a distributed database of all the LLN Nodes. 542 An extension to the Neighbor Discovery Protocol is introduced to 543 exchange Binding Table information across the Backbone Link as needed 544 for the operation of IPv6 Neighbor Discovery. 546 RFC6775 and follow-on work [RFC8505] address the needs of LLNs, and 547 similar techniques are likely to be valuable on any type of link 548 where sleeping devices are attached, or where the use of broadcast 549 and multicast operations should be limited. 551 4.3. Buffering to Improve Battery Life 553 Methods have been developed to help save battery life; for example, a 554 device might not wake up when the AP receives a multicast packet. 555 The AP acts on behalf of STAs in various ways. To enable use of the 556 power-saving feature for STAs in its BSS, the AP buffers frames for 557 delivery to the STA at the time when the STA is scheduled for 558 reception. If an AP, for instance, expresses a DTIM (Delivery 559 Traffic Indication Message) of 3 then the AP will send a multicast 560 packet every 3 packets. In fact, when any single wireless STA 561 associated with an access point has 802.11 power-save mode enabled, 562 the access point buffers all multicast frames and sends them only 563 after the next DTIM beacon. 565 In practice, most AP's will send a multicast every 30 packets. For 566 unicast the AP could send a TIM (Traffic Indication Message), but for 567 multicast the AP sends a broadcast to everyone. DTIM does power 568 management but STAs can choose whether or not to wake up and whether 569 or not to drop the packet. Unfortunately, without proper 570 administrative control, such STAs may be unable to determine why 571 their multicast operations do not work. 573 4.4. Limiting multicast buffer hardware queue depth 575 The CAB (Content after Beacon) queue is used for beacon-triggered 576 transmission of buffered multicast frames. If lots of multicast 577 frames were buffered, and this queue fills up, it drowns out all 578 regular traffic. To limit the damage that buffered traffic can do, 579 some drivers limit the amount of queued multicast data to a fraction 580 of the beacon_interval. An example of this is [CAB]. 582 4.5. IPv6 support in 802.11-2012 584 IPv6 uses NDP instead of ARP. Every IPv6 node subscribes to a 585 special multicast address for this purpose. 587 Here is the specification language from clause 10.23.13 of 588 [dot11-proxyarp]: 590 "When an IPv6 address is being resolved, the Proxy Neighbor 591 Discovery service shall respond with a Neighbor Advertisement 592 message [...] on behalf of an associated STA to an [ICMPv6] 593 Neighbor Solicitation message [...]. When MAC address mappings 594 change, the AP may send unsolicited Neighbor Advertisement 595 Messages on behalf of a STA." 597 NDP may be used to request additional information 599 o Maximum Transmission Unit 600 o Router Solicitation 601 o Router Advertisement, etc. 603 NDP messages are sent as group addressed (broadcast) frames in 604 802.11. Using the proxy operation helps to keep NDP messages off the 605 wireless medium. 607 4.6. Using Unicast Instead of Multicast 609 It is often possible to transmit multicast control and data messages 610 by using unicast transmissions to each station individually. 612 4.6.1. Overview 614 In many situations, it's a good choice to use unicast instead of 615 multicast over the Wi-Fi link. This avoids most of the problems 616 specific to multicast over Wi-Fi, since the individual frames are 617 then acknowledged and buffered for power save clients, in the way 618 that unicast traffic normally operates. 620 This approach comes with the tradeoff of sometimes sending the same 621 packet multiple times over the Wi-Fi link. However, in many cases, 622 such as video into a residential home network, this can be a good 623 tradeoff, since the Wi-Fi link may have enough capacity for the 624 unicast traffic to be transmitted to each subscribed STA, even though 625 multicast addressing may have been necessary for the upstream access 626 network. 628 Several technologies exist that can be used to arrange unicast 629 transport over the Wi-Fi link, outlined in the subsections below. 631 4.6.2. Layer 2 Conversion to Unicast 633 It is often possible to transmit multicast control and data messages 634 by using unicast transmissions to each station individually. 636 Although there is not yet a standardized method of conversion, at 637 least one widely available implementation exists in the Linux 638 bridging code [bridge-mc-2-uc]. Other proprietary implementations 639 are available from various vendors. In general, these 640 implementations perform a straightforward mapping for groups or 641 channels, discovered by IGMP or MLD snooping, to the corresponding 642 unicast MAC addresses. 644 4.6.3. Directed Multicast Service (DMS) 646 There are situations where more is needed than simply converting 647 multicast to unicast. For these purposes, DMS enables an STA to 648 request that the AP transmit multicast group addressed frames 649 destined to the requesting STAs as individually addressed frames 650 [i.e., convert multicast to unicast]. Here are some characteristics 651 of DMS: 653 o Requires 802.11n A-MSDUs 654 o Individually addressed frames are acknowledged and are buffered 655 for power save STAs 656 o The requesting STA may specify traffic characteristics for DMS 657 traffic 658 o DMS was defined in IEEE Std 802.11v-2011 659 o DMS requires changes to both AP and STA implementation. 661 DMS is not currently implemented in products. See [Tramarin2017] and 662 [Oliva2013] for more information. 664 4.6.4. Automatic Multicast Tunneling (AMT) 666 AMT[RFC7450] provides a method to tunnel multicast IP packets inside 667 unicast IP packets over network links that only support unicast. 668 When an operating system or application running on an STA has an AMT 669 gateway capability integrated, it's possible to use unicast to 670 traverse the Wi-Fi link by deploying an AMT relay in the non-Wi-Fi 671 portion of the network connected to the AP. 673 It is recommended that multicast-enabled networks deploying AMT 674 relays for this purpose make the relays locally discoverable with the 675 following methods, as described in 676 [I-D.ietf-mboned-driad-amt-discovery]: 678 o DNS-SD [RFC6763] 679 o the well-known IP addresses from Section 7 of [RFC7450] 681 An AMT gateway that implements multiple standard discovery methods is 682 more likely to discover the local multicast-capable network, instead 683 of forming a connection to a non-local AMT relay further upstream. 685 4.7. GroupCast with Retries (GCR) 687 GCR (defined in [dot11aa]) provides greater reliability by using 688 either unsolicited retries or a block acknowledgement mechanism. GCR 689 increases probability of broadcast frame reception success, but still 690 does not guarantee success. 692 For the block acknowledgement mechanism, the AP transmits each group 693 addressed frame as conventional group addressed transmission. 694 Retransmissions are group addressed, but hidden from non-11aa STAs. 695 A directed block acknowledgement scheme is used to harvest reception 696 status from receivers; retransmissions are based upon these 697 responses. 699 GCR is suitable for all group sizes including medium to large groups. 700 As the number of devices in the group increases, GCR can send block 701 acknowledgement requests to only a small subset of the group. GCR 702 does require changes to both AP and STA implementations. 704 GCR may introduce unacceptable latency. After sending a group of 705 data frames to the group, the AP has do the following: 707 o unicast a Block Ack Request (BAR) to a subset of members. 708 o wait for the corresponding Block Ack (BA). 709 o retransmit any missed frames. 710 o resume other operations that may have been delayed. 712 This latency may not be acceptable for some traffic. 714 There are ongoing extensions in 802.11 to improve GCR performance. 716 o BAR is sent using downlink MU-MIMO (note that downlink MU-MIMO is 717 already specified in 802.11-REVmc 4.3). 718 o BA is sent using uplink MU-MIMO (which is a .11ax feature). 719 o Additional 802.11ax extensions are under consideration; see 720 [mc-ack-mux] 721 o Latency may also be reduced by simultaneously receiving BA 722 information from multiple STAs. 724 5. Operational optimizations 726 This section lists some operational optimizations that can be 727 implemented when deploying wireless IEEE 802 networks to mitigate the 728 issues discussed in Section 3. 730 5.1. Mitigating Problems from Spurious Neighbor Discovery 732 ARP Sponges 734 An ARP Sponge sits on a network and learns which IP addresses 735 are actually in use. It also listen for ARP requests, and, if 736 it sees an ARP for an IP address that it believes is not used, 737 it will reply with its own MAC address. This means that the 738 router now has an IP to MAC mapping, which it caches. If that 739 IP is later assigned to an machine (e.g using DHCP), the ARP 740 sponge will see this, and will stop replying for that address. 741 Gratuitous ARPs (or the machine ARPing for its gateway) will 742 replace the sponged address in the router ARP table. This 743 technique is quite effective; but, unfortunately, the ARP 744 sponge daemons were not really designed for this use (one of 745 the most widely deployed arp sponges [arpsponge], was designed 746 to deal with the disappearance of participants from an IXP) and 747 so are not optimized for this purpose. One daemon is needed 748 per subnet, the tuning is tricky (the scanning rate versus the 749 population rate versus retires, etc.) and sometimes buggy 750 daemons have stopped, requiring a restart of the daemon and 751 causing disruption. 753 Router mitigations 755 Some routers (often those based on Linux) implement a "negative 756 ARP cache" daemon. Simply put, if the router does not see a 757 reply to an ARP it can be configured to cache this information 758 for some interval. Unfortunately, the core routers in use 759 often do not support this. When a host connects to a network 760 and gets an IP address, it will ARP for its default gateway 761 (the router). The router will update its cache with the IP to 762 host MAC mapping learned from the request (passive ARP 763 learning). 765 Firewall unused space 767 The distribution of users on wireless networks / subnets may 768 change in various use cases, such as conference venues (e.g 769 SSIDs are renamed, some SSIDs lose favor, etc). This makes 770 utilization for particular SSIDs difficult to predict ahead of 771 time, but usage can be monitored as attendees use the different 772 networks. Configuring multiple DHCP pools per subnet, and 773 enabling them sequentially, can create a large subnet, from 774 which only addresses in the lower portions are assigned. 775 Therefore input IP access lists can be applied, which deny 776 traffic to the upper, unused portions. Then the router does 777 not attempt to forward packets to the unused portions of the 778 subnets, and so does not ARP for it. This method has proven to 779 be very effective, but is somewhat of a blunt axe, is fairly 780 labor intensive, and requires coordination. 782 Disabling/filtering ARP requests 784 In general, the router does not need to ARP for hosts; when a 785 host connects, the router can learn the IP to MAC mapping from 786 the ARP request sent by that host. Consequently it should be 787 possible to disable and / or filter ARP requests from the 788 router. Unfortunately, ARP is a very low level / fundamental 789 part of the IP stack, and is often offloaded from the normal 790 control plane. While many routers can filter layer-2 traffic, 791 this is usually implemented as an input filter and / or has 792 limited ability to filter output broadcast traffic. This means 793 that the simple "just disable ARP or filter it outbound" seems 794 like a really simple (and obvious) solution, but 795 implementations / architectural issues make this difficult or 796 awkward in practice. 798 NAT 800 The broadcasts are overwhelmingly being caused by outside 801 scanning / backscatter traffic. To NAT the entire (or a large 802 portion) of the attendee networks would eliminate NAT 803 translation entries for unused addresses, and so the router 804 would never ARP for them. However, there are many reasons to 805 avoid using NAT in such a blanket fashion. 807 Stateful firewalls 809 Another obvious solution would be to put a stateful firewall 810 between the wireless network and the Internet. This firewall 811 would block incoming traffic not associated with an outbound 812 request. But this conflicts with the need and desire of some 813 organizations to have the network as open as possible and to 814 honor the end-to-end principle. An attendee on a meeting 815 network should be an Internet host, and should be able to 816 receive unsolicited requests. Unfortunately, keeping the 817 network working and stable is the first priority and a stateful 818 firewall may be required in order to achieve this. 820 5.2. Mitigating Spurious Service Discovery Messages 822 In networks that must support hundreds of STAs, operators have 823 observed network degradation due to many devices simultaneously 824 registering with mDNS. In a network with many clients, it is 825 recommended to ensure that mDNS packets designed to discover 826 services in smaller home networks be constrained to avoid 827 disrupting other traffic. 829 6. Multicast Considerations for Other Wireless Media 831 Many of the causes of performance degradation described in earlier 832 sections are also observable for wireless media other than 802.11. 834 For instance, problems with power save, excess media occupancy, and 835 poor reliability will also affect 802.15.3 and 802.15.4. 836 Unfortunately, 802.15 media specifications do not yet include 837 mechanisms similar to those developed for 802.11. In fact, the 838 design philosophy for 802.15 is oriented towards minimality, with the 839 result that many such functions are relegated to operation within 840 higher layer protocols. This leads to a patchwork of non- 841 interoperable and vendor-specific solutions. See [uli] for some 842 additional discussion, and a proposal for a task group to resolve 843 similar issues, in which the multicast problems might be considered 844 for mitigation. 846 Similar considerations hold for most other wireless media. A brief 847 introduction is provided in [RFC5757] for the following: 849 o 802.16 WIMAX 850 o 3GPP/3GPP2 851 o DVB-H / DVB-IPDC 852 o TV Broadcast and Satellite Networks 854 7. Recommendations 856 This section provides some recommendations about the usage and 857 combinations of the multicast enhancements described in Section 4 and 858 Section 5. 860 Future protocol documents utilizing multicast signaling should be 861 carefully scrutinized if the protocol is likely to be used over 862 wireless media. 864 Proxy methods should be encouraged to conserve network bandwidth and 865 power utilization by low-power devices. The device can use a unicast 866 message to its proxy, and then the proxy can take care of any needed 867 multicast operations. 869 Multicast signaling for wireless devices should be done in a way 870 compatible with low duty-cycle operation. 872 8. On-going Discussion Items 874 This section suggests two discussion items for further resolution. 876 First, standards (and private) organizations should develop 877 guidelines to help clarify when multicast packets should be sent 878 wired rather than wireless. For example, 802.1ak [1] works on both 879 ethernet and Wi-Fi and organizations could help decision making by 880 developing guidelines for multicast over Wi-Fi including options for 881 when traffic should be sent wired. 883 Second, reliable registration to Layer-2 multicast groups, and a 884 reliable multicast operation at Layer-2, might provide a good 885 multicast over wifi solution. There shouldn't be a need to support 886 2^24 groups to get solicited node multicast working: it is possible 887 to simply select a number of trailing bits that make sense for a 888 given network size to limit the number of unwanted deliveries to 889 reasonable levels. IEEE 802.1, 802.11, and 802.15 should be 890 encouraged to revisit L2 multicast issues and provide workable 891 solutions. 893 9. Security Considerations 895 This document does not introduce or modify any security mechanisms. 896 Multicast is made more secure in a variety of ways. [RFC4601], for 897 instance, mandates the use of IPsec to ensure authentication of the 898 link-local messages in the Protocol Independent Multicast - Sparse 899 Mode (PIM-SM) routing protocol. [RFC5796]specifies mechanisms to 900 authenticate the PIM-SM link-local messages using the IP security 901 (IPsec) Encapsulating Security Payload (ESP) or (optionally) the 902 Authentication Header (AH). 904 As noted in [group_key], the unreliable nature of multicast 905 transmission over wireless media can cause subtle problems with 906 multicast group key management and updates. When WPA (TKIP) or WPA2 907 (AES-CCMP) encryption is in use, AP to client (From DS) multicasts 908 have to be encrypted with a separate encryption key that is known to 909 all of the clients (this is called the Group Key). Quoting further 910 from that website, "... most clients are able to get connected and 911 surf the web, check email, etc. even when From DS multicasts are 912 broken. So a lot of people don't realize they have multicast 913 problems on their network..." 915 10. IANA Considerations 917 This document does not request any IANA actions. 919 11. Acknowledgements 921 This document has benefitted from discussions with the following 922 people, in alphabetical order: Mikael Abrahamsson, Bill Atwood, 923 Stuart Cheshire, Donald Eastlake, Toerless Eckert, Jake Holland, Joel 924 Jaeggli, Jan Komissar, David Lamparter, Morten Pedersen, Pascal 925 Thubert, Jeffrey (Zhaohui) Zhang 927 12. References 929 12.1. Informative References 931 [arpsponge] 932 Wessel, M. and N. Sijm, "Effects of IPv4 and IPv6 address 933 resolution on AMS-IX and the ARP Sponge", July 2009, 934 . 937 [bridge-mc-2-uc] 938 Fietkau, F., "bridge: multicast to unicast", Jan 2017, 939 . 942 [CAB] Fietkau, F., "Limit multicast buffer hardware queue 943 depth", 2013, 944 . 946 [Deri-2010] 947 Deri, L. and J. Gasparakis, "10 Gbit Hardware Packet 948 Filtering Using Commodity Network Adapters", RIPE 61, 949 2010, . 952 [dot11] "IEEE 802 Wireless", "802.11-2016 - IEEE Standard for 953 Information technology--Telecommunications and information 954 exchange between systems Local and metropolitan area 955 networks--Specific requirements - Part 11: Wireless LAN 956 Medium Access Control (MAC) and Physical Layer (PHY) 957 Specification (includes 802.11v amendment)", March 2016, 958 . 961 [dot11-proxyarp] 962 Hiertz, G., Mestanov, F., and B. Hart, "Proxy ARP in 963 802.11ax", September 2015, 964 . 967 [dot11aa] "IEEE 802 Wireless", "Part 11: Wireless LAN Medium Access 968 Control (MAC) and Physical Layer (PHY) Specifications 969 Amendment 2: MAC Enhancements for Robust Audio Video 970 Streaming", March 2012, 971 . 973 [group_key] 974 Spiff, "Why do some WiFi routers block multicast packets 975 going from wired to wireless?", Jan 2017, 976 . 980 [I-D.ietf-6lo-backbone-router] 981 Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6 982 Backbone Router", draft-ietf-6lo-backbone-router-20 (work 983 in progress), March 2020. 985 [I-D.ietf-6tisch-architecture] 986 Thubert, P., "An Architecture for IPv6 over the TSCH mode 987 of IEEE 802.15.4", draft-ietf-6tisch-architecture-29 (work 988 in progress), August 2020. 990 [I-D.ietf-mboned-driad-amt-discovery] 991 Holland, J., "DNS Reverse IP AMT (Automatic Multicast 992 Tunneling) Discovery", draft-ietf-mboned-driad-amt- 993 discovery-13 (work in progress), December 2019. 995 [ietf_802-11] 996 Stanley, D., "IEEE 802.11 multicast capabilities", Nov 997 2015, . 1001 [mc-ack-mux] 1002 Tanaka, Y., Sakai, E., Morioka, Y., Mori, M., Hiertz, G., 1003 and S. Coffey, "Multiplexing of Acknowledgements for 1004 Multicast Transmission", July 2015, 1005 . 1009 [mc-prob-stmt] 1010 Abrahamsson, M. and A. Stephens, "Multicast on 802.11", 1011 March 2015, . 1014 [mc-props] 1015 Stephens, A., "IEEE 802.11 multicast properties", March 1016 2015, . 1020 [Oliva2013] 1021 de la Oliva, A., Serrano, P., Salvador, P., and A. Banchs, 1022 "Performance evaluation of the IEEE 802.11aa multicast 1023 mechanisms for video streaming", 2013 IEEE 14th 1024 International Symposium on "A World of Wireless, Mobile 1025 and Multimedia Networks" (WoWMoM) pp. 1-9, June 2013. 1027 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 1028 RFC 2131, DOI 10.17487/RFC2131, March 1997, 1029 . 1031 [RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor 1032 Discovery for IP Version 6 (IPv6)", RFC 2461, 1033 DOI 10.17487/RFC2461, December 1998, 1034 . 1036 [RFC4286] Haberman, B. and J. Martin, "Multicast Router Discovery", 1037 RFC 4286, DOI 10.17487/RFC4286, December 2005, 1038 . 1040 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 1041 "Considerations for Internet Group Management Protocol 1042 (IGMP) and Multicast Listener Discovery (MLD) Snooping 1043 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 1044 . 1046 [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 1047 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 1048 Protocol Specification (Revised)", RFC 4601, 1049 DOI 10.17487/RFC4601, August 2006, 1050 . 1052 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1053 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1054 DOI 10.17487/RFC4861, September 2007, 1055 . 1057 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1058 Address Autoconfiguration", RFC 4862, 1059 DOI 10.17487/RFC4862, September 2007, 1060 . 1062 [RFC5424] Gerhards, R., "The Syslog Protocol", RFC 5424, 1063 DOI 10.17487/RFC5424, March 2009, 1064 . 1066 [RFC5757] Schmidt, T., Waehlisch, M., and G. Fairhurst, "Multicast 1067 Mobility in Mobile IP Version 6 (MIPv6): Problem Statement 1068 and Brief Survey", RFC 5757, DOI 10.17487/RFC5757, 1069 February 2010, . 1071 [RFC5796] Atwood, W., Islam, S., and M. Siami, "Authentication and 1072 Confidentiality in Protocol Independent Multicast Sparse 1073 Mode (PIM-SM) Link-Local Messages", RFC 5796, 1074 DOI 10.17487/RFC5796, March 2010, 1075 . 1077 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1078 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1079 DOI 10.17487/RFC6282, September 2011, 1080 . 1082 [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, 1083 DOI 10.17487/RFC6762, February 2013, 1084 . 1086 [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service 1087 Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013, 1088 . 1090 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1091 Bormann, "Neighbor Discovery Optimization for IPv6 over 1092 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1093 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1094 . 1096 [RFC6970] Boucadair, M., Penno, R., and D. Wing, "Universal Plug and 1097 Play (UPnP) Internet Gateway Device - Port Control 1098 Protocol Interworking Function (IGD-PCP IWF)", RFC 6970, 1099 DOI 10.17487/RFC6970, July 2013, 1100 . 1102 [RFC7450] Bumgardner, G., "Automatic Multicast Tunneling", RFC 7450, 1103 DOI 10.17487/RFC7450, February 2015, 1104 . 1106 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 1107 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 1108 Multicast - Sparse Mode (PIM-SM): Protocol Specification 1109 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 1110 2016, . 1112 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 1113 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 1114 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 1115 RFC 8415, DOI 10.17487/RFC8415, November 2018, 1116 . 1118 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 1119 Perkins, "Registration Extensions for IPv6 over Low-Power 1120 Wireless Personal Area Network (6LoWPAN) Neighbor 1121 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 1122 . 1124 [Tramarin2017] 1125 Tramarin, F., Vitturi, S., and M. Luvisotto, "IEEE 802.11n 1126 for Distributed Measurement Systems", 2017 IEEE 1127 International Instrumentation and Measurement Technology 1128 Conference (I2MTC) pp. 1-6, May 2017. 1130 [uli] Kinney, P., "LLC Proposal for 802.15.4", Nov 2015, 1131 . 1134 12.2. URIs 1136 [1] https://www.ieee802.org/1/pages/802.1ak.html 1138 Appendix A. Changes in this draft between revisions 06 versus 07 1140 This section lists the changes between revisions ...-06.txt and 1141 ...-07.txt of draft-ietf-mboned-ieee802-mcast-problems. 1143 o Improved wording in section describing ARPsponge. 1144 o Removed DRIAD as a discovery mechanism for multicast relays. 1145 o Updated bibliographic citations, repaired broken URLs as needed. 1146 o More editorial improvements and grammatical corrections. 1148 Appendix B. Changes in this draft between revisions 05 versus 06 1150 This section lists the changes between revisions ...-05.txt and 1151 ...-06.txt of draft-ietf-mboned-ieee802-mcast-problems. 1153 o Included new text in Security Considerations to alert about 1154 problems regarding Group Key management caused by multicast 1155 unreliability and implementation bugs. 1156 o Included DRIAD as a discovery mechanism for multicast relays. 1157 o Corrected occurrences of "which" versus "that" and "amount" versus 1158 "number". 1159 o Updated bibliographic citations, included URLs as needed. 1160 o More editorial improvements and grammatical corrections. 1162 Appendix C. Changes in this draft between revisions 04 versus 05 1164 This section lists the changes between revisions ...-04.txt and 1165 ...-05.txt of draft-ietf-mboned-ieee802-mcast-problems. 1167 o Incorporated text from Jake Holland for a new section about 1168 conversion of multicast to unicast and included AMT as an existing 1169 solution. 1170 o Included some text about likely future multicast applications that 1171 will emphasize the need for attention to the technical matters 1172 collected in this document. 1173 o Further modified text to be more generic instead of referring 1174 specifically to IETF conference situations. 1175 o Modified text to be more generic instead of referring specifically 1176 to Bonjour. 1177 o Added uPnP as a representative multicast protocol in IP networks. 1179 o Referred to Linux bridging code for multicast to unicast. 1180 o Updated bibliographic citations, included URLs as needed. 1181 o More editorial improvements and grammatical corrections. 1183 Appendix D. Changes in this draft between revisions 03 versus 04 1185 This section lists the changes between revisions ...-03.txt and 1186 ...-04.txt of draft-ietf-mboned-ieee802-mcast-problems. 1188 o Replaced "client" by "STA". 1189 o Used terminology "Wi-Fi" throughout. 1190 o Many editorial improvements and grammatical corrections. 1191 o Modified text to be more generic instead of referring specifically 1192 to IETF conference situations. 1193 o Cited [RFC5757] for introduction to other wireless media. 1194 o Updated bibliographic citations. 1196 Authors' Addresses 1198 Charles E. Perkins 1199 Blue Meadow Networks 1201 Phone: +1-408-330-4586 1202 Email: charliep@computer.org 1204 Mike McBride 1205 Futurewei Technologies Inc. 1206 2330 Central Expressway 1207 Santa Clara, CA 95055 1208 USA 1210 Email: michael.mcbride@futurewei.com 1212 Dorothy Stanley 1213 Hewlett Packard Enterprise 1214 2000 North Naperville Rd. 1215 Naperville, IL 60566 1216 USA 1218 Phone: +1 630 979 1572 1219 Email: dstanley1389@gmail.com 1220 Warren Kumari 1221 Google 1222 1600 Amphitheatre Parkway 1223 Mountain View, CA 94043 1224 USA 1226 Email: warren@kumari.net 1228 Juan Carlos Zuniga 1229 SIGFOX 1230 425 rue Jean Rostand 1231 Labege 31670 1232 France 1234 Email: j.c.zuniga@ieee.org