--- 1/draft-ietf-mboned-ieee802-mcast-problems-08.txt 2019-09-26 18:13:09.931534688 -0700 +++ 2/draft-ietf-mboned-ieee802-mcast-problems-09.txt 2019-09-26 18:13:09.987536109 -0700 @@ -1,54 +1,54 @@ Internet Area C. Perkins Internet-Draft Intended status: Informational M. McBride -Expires: February 14, 2020 Futurewei +Expires: March 29, 2020 Futurewei D. Stanley HPE W. Kumari Google JC. Zuniga SIGFOX - August 13, 2019 + September 26, 2019 Multicast Considerations over IEEE 802 Wireless Media - draft-ietf-mboned-ieee802-mcast-problems-08 + draft-ietf-mboned-ieee802-mcast-problems-09 Abstract Well-known issues with multicast have prevented the deployment of multicast in 802.11 and other local-area wireless environments. This document offers guidance on known limitations and problems with - wireless multicast. Also described are certain multicast enhancement - features that have been specified by the IETF and by IEEE 802 for - wireless media, as well as some operational choices that can be taken - to improve the performace of the network. Finally, some + wireless Layer-2 multicast. Also described are certain multicast + enhancement features that have been specified by the IETF and by IEEE + 802 for wireless media, as well as some operational choices that can + be taken to improve the performance of the network. Finally, some recommendations are provided about the usage and combination of these features and operational choices. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on February 14, 2020. + This Internet-Draft will expire on March 29, 2020. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -68,45 +68,45 @@ 3.1.2. Lower and Variable Data Rate . . . . . . . . . . . . 6 3.1.3. High Interference . . . . . . . . . . . . . . . . . . 7 3.1.4. Power-save Effects on Multicast . . . . . . . . . . . 7 3.2. Issues at Layer 3 and Above . . . . . . . . . . . . . . . 7 3.2.1. IPv4 issues . . . . . . . . . . . . . . . . . . . . . 8 3.2.2. IPv6 issues . . . . . . . . . . . . . . . . . . . . . 8 3.2.3. MLD issues . . . . . . . . . . . . . . . . . . . . . 9 3.2.4. Spurious Neighbor Discovery . . . . . . . . . . . . . 9 4. Multicast protocol optimizations . . . . . . . . . . . . . . 10 4.1. Proxy ARP in 802.11-2012 . . . . . . . . . . . . . . . . 10 - 4.2. IPv6 Address Registration and Proxy Neighbor Discovery . 10 + 4.2. IPv6 Address Registration and Proxy Neighbor Discovery . 11 4.3. Buffering to Improve Battery Life . . . . . . . . . . . . 12 - 4.4. Limiting multicast buffer hardware queue depth . . . . . 12 - 4.5. IPv6 support in 802.11-2012 . . . . . . . . . . . . . . . 12 - 4.6. Using Unicast Instead of Multicast . . . . . . . . . . . 13 - 4.6.1. Overview . . . . . . . . . . . . . . . . . . . . . . 13 - 4.6.2. Layer 2 Conversion to Unicast . . . . . . . . . . . . 13 + 4.4. Limiting multicast buffer hardware queue depth . . . . . 13 + 4.5. IPv6 support in 802.11-2012 . . . . . . . . . . . . . . . 13 + 4.6. Using Unicast Instead of Multicast . . . . . . . . . . . 14 + 4.6.1. Overview . . . . . . . . . . . . . . . . . . . . . . 14 + 4.6.2. Layer 2 Conversion to Unicast . . . . . . . . . . . . 14 4.6.3. Directed Multicast Service (DMS) . . . . . . . . . . 14 - 4.6.4. Automatic Multicast Tunneling (AMT) . . . . . . . . . 14 + 4.6.4. Automatic Multicast Tunneling (AMT) . . . . . . . . . 15 4.7. GroupCast with Retries (GCR) . . . . . . . . . . . . . . 15 - 5. Operational optimizations . . . . . . . . . . . . . . . . . . 15 + 5. Operational optimizations . . . . . . . . . . . . . . . . . . 16 5.1. Mitigating Problems from Spurious Neighbor Discovery . . 16 - 5.2. Mitigating Spurious Service Discovery Messages . . . . . 17 + 5.2. Mitigating Spurious Service Discovery Messages . . . . . 18 6. Multicast Considerations for Other Wireless Media . . . . . . 18 - 7. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 18 + 7. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 19 8. Discussion Items . . . . . . . . . . . . . . . . . . . . . . 19 - 9. Security Considerations . . . . . . . . . . . . . . . . . . . 19 - 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 - 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19 + 9. Security Considerations . . . . . . . . . . . . . . . . . . . 20 + 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 + 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20 12. Informative References . . . . . . . . . . . . . . . . . . . 20 - Appendix A. Changes in this draft between revisions 06 versus 07 23 - Appendix B. Changes in this draft between revisions 05 versus 06 23 + Appendix A. Changes in this draft between revisions 06 versus 07 24 + Appendix B. Changes in this draft between revisions 05 versus 06 24 Appendix C. Changes in this draft between revisions 04 versus 05 24 - Appendix D. Changes in this draft between revisions 03 versus 04 24 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 + Appendix D. Changes in this draft between revisions 03 versus 04 25 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25 1. Introduction Well-known issues with multicast have prevented the deployment of multicast in 802.11 [dot11] and other local-area wireless environments, as described in [mc-props], [mc-prob-stmt]. Performance issues have been observed when multicast packet transmissions of IETF protocols are used over IEEE 802 wireless media. Even though enhancements for multicast transmissions have been designed at both IETF and IEEE 802, incompatibilities still @@ -149,34 +149,35 @@ lower modulation transmissions occupy the medium longer; they hamper efficient transmission of traffic using higher order modulations to nearby stations. For these and other reasons, IEEE 802 working groups such as 802.11 have designed features to improve the performance of multicast transmissions at Layer 2 [ietf_802-11]. In addition to protocol design features, certain operational and configuration enhancements can ameliorate the network performance issues created by multicast traffic, as described in Section 5. There seems to be general agreement that these problems will not be - fixed anytime soon, primarily because it's expensive to do so, and - multicast is unreliable. Compared to unicast over Wi-Fi, multicast - is often treated as somewhat a second class citizen, even though - there are many protocols using multicast. Something needs to be - provided in order to make them more reliable. IPv6 neighbor - discovery saturating the Wi-Fi link is only part of the problem. Wi- - Fi traffic classes may help. This document is intended to help make - the determination about what problems should be solved by the IETF - and what problems should be solved by the IEEE (see Section 8). + fixed anytime soon, primarily because it's expensive to do so and due + to multicast being unreliable. Compared to unicast over Wi-Fi, + multicast is often treated as somewhat of a second class citizen, + even though there are many protocols using multicast. Something + needs to be provided in order to make them more reliable. IPv6 + neighbor discovery saturating the Wi-Fi link is only part of the + problem. Wi-Fi traffic classes may help. This document is intended + to help make the determination about what problems should be solved + by the IETF and what problems should be solved by the IEEE (see + Section 8). This document details various problems caused by multicast transmission over wireless networks, including high packet error rates, no acknowledgements, and low data rate. It also explains some - enhancements that have been designed at IETF and IEEE 802 to + enhancements that have been designed at the IETF and IEEE 802 to ameliorate the effects of multicast traffic. Recommendations are also provided to implementors about how to use and combine these enhancements. Some advice about the operational choices that can be taken is also included. It is likely that this document will also be considered relevant to designers of future IEEE wireless specifications. 2. Terminology This document uses the following definitions: @@ -257,31 +258,31 @@ multicast packet; generally the Access Point has to use a much lower data rate at a power level high enough for even the farthest station to receive the packet, for example as briefly mentioned in [RFC5757]. Consequently, the data rate of a video stream, for instance, would be constrained by the environmental considerations of the least reliable receiver associated with the Access Point. Because more robust modulation and coding schemes (MCSs) have longer range but also lower data rate, multicast / broadcast traffic is generally transmitted at the slowest rate of all the connected - devices, also known as the basic rate. The amount of additional - interference depends on the specific wireless technology. In fact - backward compatibility and multi-stream implementations mean that the - maximum unicast rates are currently up to a few Gb/s, so there can be - a more than 3 orders of magnitude difference in the transmission rate - between multicast / broadcast versus optimal unicast forwarding. - Some techinues employed to increase spectral efficiency, such as - spatial multiplexing in mimo systems, are not available with more - than one intended reciever; it is not the case that backwards - compatibility is the only factor responsible for lower multicast - transmission rates. + devices. This is also known as the basic rate. The amount of + additional interference depends on the specific wireless technology. + In fact, backward compatibility and multi-stream implementations mean + that the maximum unicast rates are currently up to a few Gbps, so + there can be more than 3 orders of magnitude difference in the + transmission rate between multicast / broadcast versus optimal + unicast forwarding. Some techiques employed to increase spectral + efficiency, such as spatial multiplexing in mimo systems, are not + available with more than one intended reciever; it is not the case + that backwards compatibility is the only factor responsible for lower + multicast transmission rates. Wired multicast also affects wireless LANs when the AP extends the wired segment; in that case, multicast / broadcast frames on the wired LAN side are copied to WLAN. Since broadcast messages are transmitted at the most robust MCS, many large frames are sent at a slow rate over the air. 3.1.3. High Interference Transmissions at a lower rate require longer occupancy of the @@ -318,25 +319,26 @@ 3.2. Issues at Layer 3 and Above This section identifies some representative IETF protocols, and describes possible negative effects due to performance degradation when using multicast transmissions for control messages. Common uses of multicast include: o Control plane signaling o Neighbor Discovery o Address Resolution - o Service discovery + o Service Discovery o Applications (video delivery, stock data, etc.) o On-demand routing o Backbone construction o Other L3 protocols (non-IP) + User Datagram Protocol (UDP) is the most common transport layer protocol for multicast applications. By itself, UDP is not reliable -- messages may be lost or delivered out of order. 3.2.1. IPv4 issues The following list contains some representative multicast protocols that are used with IPv4. o ARP @@ -349,51 +351,50 @@ service discovery protocols (e.g., for finding a printer) utilize mDNS (i.e., multicast). It's often the first service that operators drop. Even if multicast snooping is utilized, many devices can register at once and cause serious network degradation. 3.2.2. IPv6 issues IPv6 makes extensive use of multicast, including the following: o DHCPv6 - o IPv6 Neighbor Discovery Protocol (NDP) - o Duplicate Address Detection (DAD) - o Address Resolution - o Service Discovery + o IPv6 Neighbor Discovery Protocol (NDP) [RFC4861] + o multicast DNS (mDNS) o Route Discovery o Decentralized Address Assignment o Geographic routing - IPv6 NDP Neighbor Solicitation (NS) messages used in DAD and Address - Lookup make use of Link-Scope multicast. In contrast to IPv4, an - IPv6 node will typically use multiple addresses, and may change them - often for privacy reasons. This intensifies the impact of multicast - messages that are associated to the mobility of a node. Router - advertisement (RA) messages are also periodically multicasted over - the Link. + IPv6 NDP Neighbor Solicitation (NS) messages used in Duplicate + Address Detection (DAD) and Address Lookup make use of Link-Scope + multicast. In contrast to IPv4, an IPv6 node will typically use + multiple addresses, and may change them often for privacy reasons. + This intensifies the impact of multicast messages that are associated + to the mobility of a node. Router advertisement (RA) messages are + also periodically multicasted over the Link. Neighbors may be considered lost if several consecutive Neighbor Discovery packets fail. 3.2.3. MLD issues - Multicast Listener Discovery(MLD) [RFC4541] is often used to identify + Multicast Listener Discovery (MLD) [RFC4541] is used to identify members of a multicast group that are connected to the ports of a switch. Forwarding multicast frames into a Wi-Fi-enabled area can use such switch support for hardware forwarding state information. However, since IPv6 makes heavy use of multicast, each STA with an IPv6 address will require state on the switch for several and possibly many multicast solicited-node addresses. Multicast addresses that do not have forwarding state installed (perhaps due to hardware memory limitations on the switch) cause frames to be flooded - on all ports of the switch. + on all ports of the switch. Some switch vendors do not support MLD, + for link-scope multicast, due to the increase it can cause in state. 3.2.4. Spurious Neighbor Discovery On the Internet there is a "background radiation" of scanning traffic (people scanning for vulnerable machines) and backscatter (responses from spoofed traffic, etc). This means that routers very often receive packets destined for IP addresses regardless of whether those IP addresses are in use. In the cases where the IP is assigned to a host, the router broadcasts an ARP request, gets back an ARP reply, and caches it; then traffic can be delivered to the host. When the @@ -402,22 +403,33 @@ populate the ARP cache, and the next time there is traffic for that IP address the router will rebroadcast the ARP requests. The rate of these ARP requests is proportional to the size of the subnets, the rate of scanning and backscatter, and how long the router keeps state on non-responding ARPs. As it turns out, this rate is inversely proportional to how occupied the subnet is (valid ARPs end up in a cache, stopping the broadcasting; unused IPs never respond, and so cause more broadcasts). Depending on the address space in use, the time of day, how occupied the subnet is, and other - unknown factors, on the order of 2000 broadcasts per second have been - observed, for instance at the NOCs during IETF face-to-face meetings. + unknown factors, thousands of broadcasts per second have been + observed. Around 2,000 broadcasts per second have been observed at + the IETF NOC during face-to-face meetings. + + With Neighbor Discovery for IPv6 [RFC2461], nodes accomplish address + resolution by multicasting a Neighbor Solicitation that asks the + target node to return its link-layer address. Neighbor Solicitation + messages are multicast to the solicited-node multicast address of the + target address. The target returns its link-layer address in a + unicast Neighbor Advertisement message. A single request-response + pair of packets is sufficient for both the initiator and the target + to resolve each other's link-layer addresses; the initiator includes + its link-layer address in the Neighbor Solicitation. On a wired network, there is not a huge difference between unicast, multicast and broadcast traffic. Due to hardware filtering (see, e.g., [Deri-2010]), inadvertently flooded traffic (or excessive ethernet multicast) on wired networks can be quite a bit less costly, compared to wireless cases where sleeping devices have to wake up to process packets. Wired Ethernets tend to be switched networks, further reducing interference from multicast. There is effectively no collision / scheduling problem except at extremely high port utilizations. @@ -462,23 +474,23 @@ 4.2. IPv6 Address Registration and Proxy Neighbor Discovery As used in this section, a Low-Power Wireless Personal Area Network (6LoWPAN) denotes a low power lossy network (LLN) that supports 6LoWPAN Header Compression (HC) [RFC6282]. A 6TiSCH network [I-D.ietf-6tisch-architecture] is an example of a 6LowPAN. In order to control the use of IPv6 multicast over 6LoWPANs, the 6LoWPAN Neighbor Discovery (6LoWPAN ND) [RFC6775] standard defines an address registration mechanism that relies on a central registry to assess - address uniqueness, as a substitute to the inefficient Duplicate - Address Detection (DAD) mechanism found in the mainstream IPv6 - Neighbor Discovery Protocol (NDP) [RFC4861][RFC4862]. + address uniqueness, as a substitute to the inefficient DAD mechanism + found in the mainstream IPv6 Neighbor Discovery Protocol (NDP) + [RFC4861][RFC4862]. The 6lo Working Group has specified an update [RFC8505] to RFC6775. Wireless devices can register their address to a Backbone Router [I-D.ietf-6lo-backbone-router], which proxies for the registered addresses with the IPv6 NDP running on a high speed aggregating backbone. The update also enables a proxy registration mechanism on behalf of the registered node, e.g. by a 6LoWPAN router to which the mobile node is attached. The general idea behind the backbone router concept is that broadcast @@ -535,38 +547,38 @@ reception. If an AP, for instance, expresses a DTIM (Delivery Traffic Indication Message) of 3 then the AP will send a multicast packet every 3 packets. In fact, when any single wireless STA associated with an access point has 802.11 power-save mode enabled, the access point buffers all multicast frames and sends them only after the next DTIM beacon. In practice, most AP's will send a multicast every 30 packets. For unicast the AP could send a TIM (Traffic Indication Message), but for multicast the AP sends a broadcast to everyone. DTIM does power - management but STAs can choose whether or not to wake up or not and - whether or not to drop the packet. Unfortunately, without proper + management but STAs can choose whether or not to wake up and whether + or not to drop the packet. Unfortunately, without proper administrative control, such STAs may be unable to determine why their multicast operations do not work. 4.4. Limiting multicast buffer hardware queue depth The CAB (Content after Beacon) queue is used for beacon-triggered transmission of buffered multicast frames. If lots of multicast frames were buffered, and this queue fills up, it drowns out all regular traffic. To limit the damage that buffered traffic can do, some drivers limit the amount of queued multicast data to a fraction of the beacon_interval. An example of this is [CAB]. 4.5. IPv6 support in 802.11-2012 - IPv6 uses Neighbor Discovery Protocol (NDP) instead of ARP. Every - IPv6 node subscribes to a special multicast address for this purpose. + IPv6 uses NDP instead of ARP. Every IPv6 node subscribes to a + special multicast address for this purpose. Here is the specification language from clause 10.23.13 of [dot11-proxyarp]: "When an IPv6 address is being resolved, the Proxy Neighbor Discovery service shall respond with a Neighbor Advertisement message [...] on behalf of an associated STA to an [ICMPv6] Neighbor Solicitation message [...]. When MAC address mappings change, the AP may send unsolicited Neighbor Advertisement Messages on behalf of a STA." @@ -640,50 +652,50 @@ 4.6.4. Automatic Multicast Tunneling (AMT) AMT[RFC7450] provides a method to tunnel multicast IP packets inside unicast IP packets over network links that only support unicast. When an operating system or application running on an STA has an AMT gateway capability integrated, it's possible to use unicast to traverse the Wi-Fi link by deploying an AMT relay in the non-Wi-Fi portion of the network connected to the AP. - It is RECOMMENDED that multicast-enabled networks deploying AMT + It is recommended that multicast-enabled networks deploying AMT relays for this purpose make the relays locally discoverable with the following methods, as described in [I-D.ietf-mboned-driad-amt-discovery]: o DNS-SD [RFC6763] o the well-known IP addresses from Section 7 of [RFC7450] An AMT gateway that implements multiple standard discovery methods is more likely to discover the local multicast-capable network, instead - of forming a connection to an AMT relay further upstream. + of forming a connection to a non-local AMT relay further upstream. 4.7. GroupCast with Retries (GCR) GCR (defined in [dot11aa]) provides greater reliability by using either unsolicited retries or a block acknowledgement mechanism. GCR increases probability of broadcast frame reception success, but still does not guarantee success. For the block acknowledgement mechanism, the AP transmits each group addressed frame as conventional group addressed transmission. Retransmissions are group addressed, but hidden from non-11aa STAs. A directed block acknowledgement scheme is used to harvest reception status from receivers; retransmissions are based upon these responses. GCR is suitable for all group sizes including medium to large groups. As the number of devices in the group increases, GCR can send block acknowledgement requests to only a small subset of the group. GCR - does require changes to both AP and STA implementation. + does require changes to both AP and STA implementations. GCR may introduce unacceptable latency. After sending a group of data frames to the group, the AP has do the following: o unicast a Block Ack Request (BAR) to a subset of members. o wait for the corresponding Block Ack (BA). o retransmit any missed frames. o resume other operations that may have been delayed. This latency may not be acceptable for some traffic. @@ -726,24 +738,25 @@ population rate versus retires, etc.) and sometimes the daemons just seem to stop, requiring a restart of the daemon and causing disruption. Router mitigations Some routers (often those based on Linux) implement a "negative ARP cache" daemon. Simply put, if the router does not see a reply to an ARP it can be configured to cache this information for some interval. Unfortunately, the core routers in use - often do not support this. When a host connects to network and - gets an IP address, it will ARP for its default gateway (the - router). The router will update its cache with the IP to host - MAC mapping learnt from the request (passive ARP learning). + often do not support this. When a host connects to a network + and gets an IP address, it will ARP for its default gateway + (the router). The router will update its cache with the IP to + host MAC mapping learned from the request (passive ARP + learning). Firewall unused space The distribution of users on wireless networks / subnets changes from one IETF meeting to the next (e.g SSIDs are renamed, some SSIDs lose favor, etc). This makes utilization for particular SSIDs difficult to predict ahead of time, but usage can be monitored as attendees use the different networks. Configuring multiple DHCP pools per subnet, and enabling them sequentially, can create a large subnet, from which only @@ -922,46 +935,46 @@ exchange between systems Local and metropolitan area networks--Specific requirements - Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specification (includes 802.11v amendment)", March 2016, . [dot11-proxyarp] Hiertz, G., Mestanov, F., and B. Hart, "Proxy ARP in 802.11ax", September 2015, - . + . [dot11aa] "IEEE 802 Wireless", "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 2: MAC Enhancements for Robust Audio Video Streaming", March 2012, - . + . [group_key] Spiff, ""Why do some WiFi routers block multicast packets going from wired to wireless?"", Jan 2017, . [I-D.ietf-6lo-backbone-router] Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6 - Backbone Router", draft-ietf-6lo-backbone-router-11 (work - in progress), February 2019. + Backbone Router", draft-ietf-6lo-backbone-router-13 (work + in progress), September 2019. [I-D.ietf-6tisch-architecture] Thubert, P., "An Architecture for IPv6 over the TSCH mode - of IEEE 802.15.4", draft-ietf-6tisch-architecture-24 (work - in progress), July 2019. + of IEEE 802.15.4", draft-ietf-6tisch-architecture-26 (work + in progress), August 2019. [I-D.ietf-mboned-driad-amt-discovery] Holland, J., "DNS Reverse IP AMT Discovery", draft-ietf- mboned-driad-amt-discovery-08 (work in progress), June 2019. [ietf_802-11] Stanley, D., "IEEE 802.11 multicast capabilities", Nov 2015, . [Oliva2013] de la Oliva, A., Serrano, P., Salvador, P., and A. Banchs, "Performance evaluation of the IEEE 802.11aa multicast mechanisms for video streaming", 2013 IEEE 14th International Symposium on "A World of Wireless, Mobile and Multimedia Networks" (WoWMoM) pp. 1-9, June 2013. + [RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor + Discovery for IP Version 6 (IPv6)", RFC 2461, + DOI 10.17487/RFC2461, December 1998, + . + [RFC4541] Christensen, M., Kimball, K., and F. Solensky, "Considerations for Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Snooping Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, . [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, DOI 10.17487/RFC4861, September 2007, . @@ -1049,22 +1067,22 @@ Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, . [Tramarin2017] Tramarin, F., Vitturi, S., and M. Luvisotto, "IEEE 802.11n for Distributed Measurement Systems", 2017 IEEE International Instrumentation and Measurement Technology Conference (I2MTC) pp. 1-6, May 2017. [uli] Kinney, P., "LLC Proposal for 802.15.4", Nov 2015, - . + . Appendix A. Changes in this draft between revisions 06 versus 07 This section lists the changes between revisions ...-06.txt and ...-07.txt of draft-ietf-mboned-ieee802-mcast-problems. o Improved wording in section describing ARPsponge. o Removed DRIAD as a discovery mechanism for multicast relays. o Updated bibliographic citations, repaired broken URLs as needed. o More editorial improvements and grammatical corrections.