--- 1/draft-ietf-mboned-ieee802-mcast-problems-03.txt 2018-11-28 08:13:11.181383436 -0800 +++ 2/draft-ietf-mboned-ieee802-mcast-problems-04.txt 2018-11-28 08:13:11.225384506 -0800 @@ -1,213 +1,215 @@ Internet Area C. Perkins Internet-Draft M. McBride Intended status: Informational Futurewei -Expires: April 26, 2019 D. Stanley +Expires: June 1, 2019 D. Stanley HPE W. Kumari Google JC. Zuniga SIGFOX - October 23, 2018 + November 28, 2018 Multicast Considerations over IEEE 802 Wireless Media - draft-ietf-mboned-ieee802-mcast-problems-03 + draft-ietf-mboned-ieee802-mcast-problems-04 Abstract Well-known issues with multicast have prevented the deployment of multicast in 802.11 [dot11], [mc-props], [mc-prob-stmt], and other - local-area wireless environments. IETF multicast experts have been - meeting together to discuss these issues and provide IEEE updates. - The mboned working group is chartered to receive regular reports on - the current state of the deployment of multicast technology, create - "practice and experience" documents that capture the experience of - those who have deployed and are deploying various multicast - technologies, and provide feedback to other relevant working groups. - This document offers guidance on known limitations and problems with - wireless multicast. Also described are various multicast enhancement - features that have been specified at IETF and IEEE 802 for wireless - media, as well as some operational chioces that can be taken to - improve the performace of the network. Finally, some recommendations - are provided about the usage and combination of these features and - operational choices. + 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 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 April 26, 2019. + + This Internet-Draft will expire on June 1, 2019. Copyright Notice Copyright (c) 2018 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 carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 3. Identified mulitcast issues . . . . . . . . . . . . . . . . . 5 + 3. Identified multicast issues . . . . . . . . . . . . . . . . . 5 3.1. Issues at Layer 2 and Below . . . . . . . . . . . . . . . 5 3.1.1. Multicast reliability . . . . . . . . . . . . . . . . 5 3.1.2. Lower and Variable Data Rate . . . . . . . . . . . . 5 3.1.3. High Interference . . . . . . . . . . . . . . . . . . 6 - 3.1.4. Power-save Effects on Multicast . . . . . . . . . . . 6 + 3.1.4. Power-save Effects on Multicast . . . . . . . . . . . 7 3.2. Issues at Layer 3 and Above . . . . . . . . . . . . . . . 7 - 3.2.1. IPv4 issues . . . . . . . . . . . . . . . . . . . . . 7 + 3.2.1. IPv4 issues . . . . . . . . . . . . . . . . . . . . . 8 3.2.2. IPv6 issues . . . . . . . . . . . . . . . . . . . . . 8 3.2.3. MLD issues . . . . . . . . . . . . . . . . . . . . . 8 3.2.4. Spurious Neighbor Discovery . . . . . . . . . . . . . 9 - 4. Multicast protocol optimizations . . . . . . . . . . . . . . 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 4.3. Buffering to Improve Battery Life . . . . . . . . . . . . 12 4.4. IPv6 support in 802.11-2012 . . . . . . . . . . . . . . . 12 4.5. Conversion of multicast to unicast . . . . . . . . . . . 13 4.6. Directed Multicast Service (DMS) . . . . . . . . . . . . 13 4.7. GroupCast with Retries (GCR) . . . . . . . . . . . . . . 13 5. Operational optimizations . . . . . . . . . . . . . . . . . . 14 5.1. Mitigating Problems from Spurious Neighbor Discovery . . 14 6. Multicast Considerations for Other Wireless Media . . . . . . 16 7. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 16 8. Discussion Items . . . . . . . . . . . . . . . . . . . . . . 17 9. Security Considerations . . . . . . . . . . . . . . . . . . . 17 - 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 - 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17 + 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 + 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18 12. Informative References . . . . . . . . . . . . . . . . . . . 18 + Appendix A. Changes between draft-ietf-mboned-ieee802-mcast- + problems revisions 03 versus 04 . . . . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 1. Introduction Performance issues have been observed when multicast packet transmissions of IETF protocols are used over IEEE 802 wireless - media. Even though enhamcements for multicast transmissions have + media. Even though enhancements for multicast transmissions have been designed at both IETF and IEEE 802, incompatibilities still exist between specifications, implementations and configuration choices. Many IETF protocols depend on multicast/broadcast for delivery of control messages to multiple receivers. Multicast is used for - various purposes such as neighborhood discovery, network flooding, + various purposes such as neighbor discovery, network flooding, address resolution, as well minimizing media occupancy for the transmission of data that is intended for multiple receivers. In addition to protocol use of broadcast/multicast for control messages, - more applications, such as push to talk in hospitals, video in - enterprises and lectures in Universities, are streaming over wifi. - Many types of end devices are increasingly using wifi for their + more applications, such as push to talk in hospitals, or video in + enterprises, universities, and homes, are sending multicast IP to end + user devices, which are increasingly using wifi for their connectivity. IETF protocols typically rely on network protocol layering in order to reduce or eliminate any dependence of higher level protocols on the specific nature of the MAC layer protocols or the physical media. In the case of multicast transmissions, higher level protocols have traditionally been designed as if transmitting a packet to an IP address had the same cost in interference and network media access, regardless of whether the destination IP address is a unicast address or a multicast or broadcast address. This model was reasonable for networks where the physical medium was wired, like Ethernet. Unfortunately, for many wireless media, the costs to access the - medium can be quite different. Multicast over wifi has often been + medium can be quite different. Multicast over Wi-Fi has often been plagued by such poor performance that it is disallowed. Some enhancements have been designed in IETF protocols that are assumed to work primarily over wireless media. However, these enhancements are usually implemented in limited deployments and not widespread on most wireless networks. IEEE 802 wireless protocols have been designed with certain features to support multicast traffic. For instance, lower modulations are used to transmit multicast frames, so that these can be received by all stations in the cell, regardless of the distance or path attenuation from the base station or access point. However, these 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. + issues created by multicast traffic, as described in Section 5. - In discussing these issues over email, and in a side meeting at IETF - 99, it has been generally agreed that these problems will not be - fixed anytime soon primarily because it's expensive to do so and - multicast is unreliable. A big problem is that multicast is somewhat - a second class citizen, to unicast, over wifi. There are many - protocols using multicast and there needs to be something provided in - order to make them more reliable. The problem of IPv6 neighbor - discovery saturating the wifi link is only part of the problem. Wifi - traffic classes may help. We need to determine what problem should - be solved by the IETF and what problem should be solved by the IEEE - (see Section 8). A "multicast over wifi" IETF mailing list has been - formed (mcast-wifi@ietf.org) for further discussion. This draft will - be updated according to the current state of discussion. + 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). 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 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: + ACK + IEEE 802.11 Access Point + AP - IEEE 802.11 Access Point. + The 802.11 layer 2 acknowledgement basic rate - The "lowest common denominator" data rate at which multicast and - broadcast traffic is generally transmitted. + The slowest rate of all the connected devices, at which multicast + and broadcast traffic is generally transmitted DTIM Delivery Traffic Indication Map (DTIM): An information element that advertises whether or not any associated stations have - buffered multicast or broadcast frames. + buffered multicast or broadcast frames MCS - Modulation and Coding Scheme. + Modulation and Coding Scheme + + NOC + Network Operations Center + + PER + Packet Error Rate STA - 802.11 station (e.g. handheld device). + 802.11 station (e.g. handheld device) TIM Traffic Indication Map (TIM): An information element that advertises whether or not any associated stations have buffered - unicast frames. + unicast frames -3. Identified mulitcast issues +3. Identified multicast issues 3.1. Issues at Layer 2 and Below In this section we describe some of the issues related to the use of multicast transmissions over IEEE 802 wireless technologies. 3.1.1. Multicast reliability Multicast traffic is typically much less reliable than unicast traffic. Since multicast makes point-to-multipoint communications, @@ -221,67 +223,68 @@ for wireless links is much worse, and is quite sensitive to the presence of background traffic. Consequently, there can be a high packet error rate (PER) due to lack of retransmission, and because the sender never backs off. It is not uncommon for there to be a packet loss rate of 5% or more, which is particularly troublesome for video and other environments where high data rates and high reliability are required. 3.1.2. Lower and Variable Data Rate - One big difference between multicast over wired versus multicast over - wired is that transmission over wired links often occurs at a fixed - rate. Wifi, on the other hand, has a transmission rate which varies - depending upon the client's proximity to the AP. The throughput of - video flows, and the capacity of the broader wifi network, will - change and will impact the ability for QoS solutions to effectively - reserve bandwidth and provide admission control. + Multicast over wired differs from multicast over wireless because + transmission over wired links often occurs at a fixed rate. Wi-Fi, + on the other hand, has a transmission rate which varies depending + upon the STA's proximity to the AP. The throughput of video flows, + and the capacity of the broader Wi-Fi network, will change and will + impact the ability for QoS solutions to effectively reserve bandwidth + and provide admission control. - For wireless stations associated with an Access Points, the power + For wireless stations associated with an Access Point, the power necessary for good reception can vary from station to station. For unicast, the goal is to minimize power requirements while maximizing the data rate to the destination. For multicast, the goal is simply to maximize the number of receivers that will correctly receive the 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. 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. + 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 lowest common denominator rate, 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 the basic rates to 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. + 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. 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 wireless medium and thus take away from the airtime of other communications and degrade the overall capacity. Furthermore, transmission at higher power, as is required to reach all multicast - clients associated to the AP, proportionately increases the area of + STAs associated to the AP, proportionately increases the area of interference. 3.1.4. Power-save Effects on Multicast One of the characteristics of multicast transmission is that every station has to be configured to wake up to receive the multicast, even though the received packet may ultimately be discarded. This process can have a large effect on the power consumption by the multicast receiver station. @@ -345,73 +348,65 @@ o IPv6 Neighbor Discovery Protocol (NDP) o Duplicate Address Detection (DAD) o Address Resolution o Service Discovery 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 multiplies 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 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 multiplies the impact of multicast - messages that are associated to the mobility of a Node. Router + 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 members of a multicast group that are connected to the ports of a - switch. Forwarding multicast frames into a WiFi-enabled area can use - such switch support for hardware forwarding state information. + 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. 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 machines whose IP addresses may or may - not be in use. In the cases where the IP is assigned to a host, the + receive packets destined for IP addresses regardless of whether they + 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 IP address is not in use, the router broadcasts one (or more) ARP requests, and never gets a reply. This means that it does not 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 at the IETF NOCs. + observed, for instance at the NOCs during IETF face-to-face meetings. 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 high amounts of 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. @@ -461,23 +456,22 @@ (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]. - The 6lo Working Group has specified an update - [I-D.ietf-6lo-rfc6775-update] to RFC6775. Wireless devices can - register their address to a Backbone Router + 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 and multicast messaging should be tightly controlled in a variety of Wireless Local Area Networks (WLANs) and Wireless Personal Area Networks (WPANs). Connectivity to a particular link that provides @@ -509,46 +503,46 @@ LLN nodes can move freely from an LLN anchored at one IPv6 Backbone Router to an LLN anchored at another Backbone Router on the same backbone, keeping any of the IPv6 addresses they have configured. The Backbone Routers maintain a Binding Table of their Registered Nodes, which serves as a distributed database of all the LLN Nodes. An extension to the Neighbor Discovery Protocol is introduced to exchange Binding Table information across the Backbone Link as needed for the operation of IPv6 Neighbor Discovery. - RFC6775 and follow-on work (e.g., [I-D.ietf-6lo-ap-nd], do address - the needs of LLNs, and similar techniques are likely to be valuable - on any type of link where sleeping devices are attached, or where the - use of broadcast and multicast operations should be limited. + RFC6775 and follow-on work [RFC8505] address the needs of LLNs, and + similar techniques are likely to be valuable on any type of link + where sleeping devices are attached, or where the use of broadcast + and multicast operations should be limited. 4.3. Buffering to Improve Battery Life Methods have been developed to help save battery life; for example, a device might not wake up when the AP receives a multicast packet. The AP acts on behalf of STAs in various ways. To enable use of the power-saving feature for STAs in its BSS, the AP buffers frames for delivery to the STA at the time when the STA is scheduled for 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 client + 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. - But in practice, most AP's will send a multicast every 30 packets. - For unicast there's a TIM (Traffic Indication Message); but since - multicast is going to everyone, the AP sends a broadcast to everyone. - DTIM does power management but clients can choose whether or not to - wake up or not and whether or not to drop the packet. Unfortunately, - without proper administrative control, such clients may no longer be - able to determine why their multicast operations do not work. + 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 + administrative control, such STAs may be unable to determine why + their multicast operations do not work. 4.4. 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. Here is the specification language from clause 10.23.13 of [dot11-proxyarp]: "When an IPv6 address is being resolved, the Proxy Neighbor @@ -569,49 +563,49 @@ wireless medium. 4.5. Conversion of multicast to unicast It is often possible to transmit multicast control and data messages by using unicast transmissions to each station individually. 4.6. Directed Multicast Service (DMS) There are situations where more is needed than simply converting - multicast to unicast. For these purposes, DMS enables a client to + multicast to unicast. For these purposes, DMS enables a STA to request that the AP transmit multicast group addressed frames - destined to the requesting clients as individually addressed frames + destined to the requesting STAs as individually addressed frames [i.e., convert multicast to unicast]. Here are some characteristics of DMS: o Requires 802.11n A-MSDUs o Individually addressed frames are acknowledged and are buffered - for power save clients + for power save STAs o The requesting STA may specify traffic characteristics for DMS traffic o DMS was defined in IEEE Std 802.11v-2011 o DMS requires changes to both AP and STA implementation. DMS is not currently implemented in products. See [Tramarin2017] and [Oliva2013] for more information. 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 - clients. A directed block acknowledgement scheme is used to harvest - reception status from receivers; retransmissions are based upon these + 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. GCR may introduce unacceptable latency. After sending a group of data frames to the group, the AP has do the following: @@ -624,21 +618,21 @@ This latency may not be acceptable for some traffic. There are ongoing extensions in 802.11 to improve GCR performance. o BAR is sent using downlink MU-MIMO (note that downlink MU-MIMO is already specified in 802.11-REVmc 4.3). o BA is sent using uplink MU-MIMO (which is a .11ax feature). o Additional 802.11ax extensions are under consideration; see [mc-ack-mux] o Latency may also be reduced by simultaneously receiving BA - information from multiple clients. + information from multiple STAs. 5. Operational optimizations This section lists some operational optimizations that can be implemented when deploying wireless IEEE 802 networks to mitigate the issues discussed in Section 3. 5.1. Mitigating Problems from Spurious Neighbor Discovery ARP Sponges @@ -669,33 +663,33 @@ for some interval. Unfortunately, the core routers which we are using 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). Firewall unused space The distribution of users on wireless networks / subnets - changes from meeting to meeting (e.g the "IETF-secure" SSID was - renamed to "IETF", fewer users use "IETF-legacy", etc). This - utilization is difficult to predict ahead of time, but we can - monitor the usage as attendees use the different networks. By - configuring multiple DHCP pools per subnet, and enabling them - sequentially, we can have a large subnet, but only assign - addresses from the lower portions of it. This means that we - can apply input IP access lists, which deny traffic to the - upper, unused portions. This means that the router does not - attempt to forward packets to the unused portions of the - subnets, and so does not ARP for it. This method has proven to - be very effective, but is somewhat of a blunt axe, is fairly - labor intensive, and requires coordination. + changes from meeting to meeting (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 addresses in the + lower portions are assigned. Therefore input IP access lists + can be applied, which deny traffic to the upper, unused + portions. Then the router does not attempt to forward packets + to the unused portions of the subnets, and so does not ARP for + it. This method has proven to be very effective, but is + somewhat of a blunt axe, is fairly labor intensive, and + requires coordination. Disabling/filtering ARP requests In general, the router does not need to ARP for hosts; when a host connects, the router can learn the IP to MAC mapping from the ARP request sent by that host. This means that we should be able to disable and / or filter ARP requests from the router. Unfortunately, ARP is a very low level / fundamental part of the IP stack, and is often offloaded from the normal control plane. While many routers can filter layer-2 traffic, @@ -705,55 +699,61 @@ like a really simple (and obvious) solution, but implementations / architectural issues make this difficult or awkward in practice. NAT The broadcasts are overwhelmingly being caused by outside scanning / backscatter traffic. This means that, if we were to NAT the entire (or a large portion) of the attendee networks, there would be no NAT translation entries for unused addresses, - and so the router would never ARP for them. The IETF NOC has - discussed NATing the entire (or large portions) attendee - address space, but a: elegance and b: flaming torches and - pitchfork concerns means we have not attempted this yet. + and so the router would never ARP for them. However, there are + many reasons to avoid using NAT in such a blanket fashion. Stateful firewalls Another obvious solution would be to put a stateful firewall between the wireless network and the Internet. This firewall would block incoming traffic not associated with an outbound - request. The IETF philosophy has been to have the network as - open as possible / honor the end-to-end principle. An attendee - on the meeting network should be an Internet host, and should - be able to receive unsolicited requests. Unfortunately, - keeping the network working and stable is the first priority - and a stateful firewall may be required in order to achieve - this. + request. But this conflicts with the need and desire to have + the network as open as possible / honor the end-to-end + principle. An attendee on the meeting network should be an + Internet host, and should be able to receive unsolicited + requests. Unfortunately, keeping the network working and + stable is the first priority and a stateful firewall may be + required in order to achieve this. 6. Multicast Considerations for Other Wireless Media Many of the causes of performance degradation described in earlier sections are also observable for wireless media other than 802.11. For instance, problems with power save, excess media occupancy, and poor reliability will also affect 802.15.3 and 802.15.4. Unfortunately, 802.15 media specifications do not yet include mechanisms similar to those developed for 802.11. In fact, the design philosophy for 802.15 is oriented towards minimality, with the result that many such functions are relegated to operation within higher layer protocols. This leads to a patchwork of non- interoperable and vendor-specific solutions. See [uli] for some additional discussion, and a proposal for a task group to resolve similar issues, in which the multicast problems might be considered for mitigation. + Similar considerations hold for most other wireless media. A brief + introduction is provided in [RFC5757] for the following: + + o 802.16 WIMAX + o 3GPP/3GPP2 + o DVB-H / DVB-IPDC + o TV Broadcast and Satellite Networks + 7. Recommendations This section will provide some recommendations about the usage and combinations of the multicast enhancements described in Section 4 and Section 5. Future protocol documents utilizing multicast signaling should be carefully scrutinized if the protocol is likely to be used over wireless media. @@ -766,30 +766,30 @@ compatible with low-duty cycle operation. (FFS) 8. Discussion Items This section suggests two discussion items for further resolution. The IETF should determine guidelines by which it may be decided that multicast packets are to be sent wired. For example, 802.1ak works - on ethernet and wifi. 802.1ak has been pulled into 802.1Q as of + on ethernet and Wi-Fi. 802.1ak has been pulled into 802.1Q as of 802.1Q-2011. 802.1Q-2014 can be found here: http://www.ieee802.org/1/pages/802.1Q-2014.html. If a generic - solution is not found, guidelines for multicast over wifi should be + solution is not found, guidelines for multicast over Wi-Fi should be established. - Perhaps a reliable registration to Layer-2 multicast groups and a - reliable multicast operation at Layer-2 could provide a generic - solution. There is no need to support 2^24 groups to get solicited - node multicast working: it is possible to simply select a number of + Reliable registration to Layer-2 multicast groups and a reliable + multicast operation at Layer-2 might provide a generic solution. + There is no need to support 2^24 groups to get solicited node + multicast working: it is possible to simply select a number of trailing bits that make sense for a given network size to limit the amount of unwanted deliveries to reasonable levels. IEEE 802.1, 802.11, and 802.15 should be encouraged to revisit L2 multicast issues. In reality, Wi-Fi provides a broadcast service, not a multicast service. On the physical medium, all frames are broadcast except in very unusual cases in which special beamforming transmitters are used. Unicast offers the advantage of being much faster (2 orders of magnitude) and much more reliable (L2 ARQ). 9. Security Considerations @@ -797,66 +797,59 @@ This document does not introduce any security mechanisms, and does not have affect existing security mechanisms. 10. IANA Considerations This document does not request any IANA actions. 11. Acknowledgements This document has benefitted from discussions with the following - people, in alphabetical order: Pascal Thubert + people, in alphabetical order: Mikael Abrahamsson, Stuart Cheshire, + Donald Eastlake, Toerless Eckert, Jake Holland, Joel Jaeggli, Pascal + Thubert 12. Informative References [arpsponge] Arien Vijn, Steven Bakker, "Arp Sponge", March 2015. [Deri-2010] Deri, L. and J. Gasparakis, "10 Gbit Hardware Packet Filtering Using Commodity Network Adapters", RIPE 61, 2010, . - [dot11] P802.11, "Part 11: Wireless LAN Medium Access Control - (MAC) and Physical Layer (PHY) Specifications", March - 2012. + [dot11] P802.11, "802.11-2016 - IEEE Standard for Information + technology--Telecommunications and information exchange + between systems Local and metropolitan area networks-- + Specific requirements - Part 11: Wireless LAN Medium + Access Control (MAC) and Physical Layer (PHY) + Specification", March 2016. [dot11-proxyarp] P802.11, "Proxy ARP in 802.11ax", September 2015. [dot11aa] P802.11, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 2: MAC Enhancements for Robust Audio Video Streaming", March 2012. - [I-D.ietf-6lo-ap-nd] - Thubert, P., Sarikaya, B., Sethi, M., and R. Struik, - "Address Protected Neighbor Discovery for Low-power and - Lossy Networks", draft-ietf-6lo-ap-nd-08 (work in - progress), October 2018. - [I-D.ietf-6lo-backbone-router] Thubert, P. and C. Perkins, "IPv6 Backbone Router", draft- ietf-6lo-backbone-router-08 (work in progress), October 2018. - [I-D.ietf-6lo-rfc6775-update] - Thubert, P., Nordmark, E., Chakrabarti, S., and C. - Perkins, "Registration Extensions for 6LoWPAN Neighbor - Discovery", draft-ietf-6lo-rfc6775-update-21 (work in - progress), June 2018. - [I-D.ietf-6tisch-architecture] Thubert, P., "An Architecture for IPv6 over the TSCH mode - of IEEE 802.15.4", draft-ietf-6tisch-architecture-15 (work - in progress), October 2018. + of IEEE 802.15.4", draft-ietf-6tisch-architecture-17 (work + in progress), November 2018. [ietf_802-11] Dorothy Stanley, "IEEE 802.11 multicast capabilities", Nov 2015. [mc-ack-mux] Yusuke Tanaka et al., "Multiplexing of Acknowledgements for Multicast Transmission", July 2015. [mc-prob-stmt] @@ -883,39 +876,64 @@ [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, . [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, DOI 10.17487/RFC4862, September 2007, . + [RFC5757] Schmidt, T., Waehlisch, M., and G. Fairhurst, "Multicast + Mobility in Mobile IP Version 6 (MIPv6): Problem Statement + and Brief Survey", RFC 5757, DOI 10.17487/RFC5757, + February 2010, . + [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, DOI 10.17487/RFC6282, September 2011, . [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. Bormann, "Neighbor Discovery Optimization for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)", RFC 6775, DOI 10.17487/RFC6775, November 2012, . + [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. + Perkins, "Registration Extensions for IPv6 over Low-Power + Wireless Personal Area Network (6LoWPAN) Neighbor + 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] Pat Kinney, "LLC Proposal for 802.15.4", Nov 2015. +Appendix A. Changes between draft-ietf-mboned-ieee802-mcast-problems + revisions 03 versus 04 + + This section lists the changes between revisions ...-03.txt and + ...-04.txt of draft-ietf-mboned-ieee802-mcast-problems. + + o Replaced "client" by "STA". + o Used terminology "Wi-Fi" throughout. + o Many editorial improvements and grammatical corrections. + o Modified text to be more generic instead of referring specifically + to IETF conference situations. + o Cited RFC 5757 [RFC5757] for introduction to other wireless media. + o Updated bibliographic citations. + Authors' Addresses Charles E. Perkins Futurewei Inc. 2330 Central Expressway Santa Clara, CA 95050 USA Phone: +1-408-330-4586 Email: charliep@computer.org