draft-ietf-mboned-ieee802-mcast-problems-08.txt   draft-ietf-mboned-ieee802-mcast-problems-09.txt 
Internet Area C. Perkins Internet Area C. Perkins
Internet-Draft Internet-Draft
Intended status: Informational M. McBride Intended status: Informational M. McBride
Expires: February 14, 2020 Futurewei Expires: March 29, 2020 Futurewei
D. Stanley D. Stanley
HPE HPE
W. Kumari W. Kumari
Google Google
JC. Zuniga JC. Zuniga
SIGFOX SIGFOX
August 13, 2019 September 26, 2019
Multicast Considerations over IEEE 802 Wireless Media Multicast Considerations over IEEE 802 Wireless Media
draft-ietf-mboned-ieee802-mcast-problems-08 draft-ietf-mboned-ieee802-mcast-problems-09
Abstract Abstract
Well-known issues with multicast have prevented the deployment of Well-known issues with multicast have prevented the deployment of
multicast in 802.11 and other local-area wireless environments. This multicast in 802.11 and other local-area wireless environments. This
document offers guidance on known limitations and problems with document offers guidance on known limitations and problems with
wireless multicast. Also described are certain multicast enhancement wireless Layer-2 multicast. Also described are certain multicast
features that have been specified by the IETF and by IEEE 802 for enhancement features that have been specified by the IETF and by IEEE
wireless media, as well as some operational choices that can be taken 802 for wireless media, as well as some operational choices that can
to improve the performace of the network. Finally, some be taken to improve the performance of the network. Finally, some
recommendations are provided about the usage and combination of these recommendations are provided about the usage and combination of these
features and operational choices. features and operational choices.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." 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 Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 37 skipping to change at page 2, line 37
3.1.2. Lower and Variable Data Rate . . . . . . . . . . . . 6 3.1.2. Lower and Variable Data Rate . . . . . . . . . . . . 6
3.1.3. High Interference . . . . . . . . . . . . . . . . . . 7 3.1.3. High Interference . . . . . . . . . . . . . . . . . . 7
3.1.4. Power-save Effects on Multicast . . . . . . . . . . . 7 3.1.4. Power-save Effects on Multicast . . . . . . . . . . . 7
3.2. Issues at Layer 3 and Above . . . . . . . . . . . . . . . 7 3.2. Issues at Layer 3 and Above . . . . . . . . . . . . . . . 7
3.2.1. IPv4 issues . . . . . . . . . . . . . . . . . . . . . 8 3.2.1. IPv4 issues . . . . . . . . . . . . . . . . . . . . . 8
3.2.2. IPv6 issues . . . . . . . . . . . . . . . . . . . . . 8 3.2.2. IPv6 issues . . . . . . . . . . . . . . . . . . . . . 8
3.2.3. MLD issues . . . . . . . . . . . . . . . . . . . . . 9 3.2.3. MLD issues . . . . . . . . . . . . . . . . . . . . . 9
3.2.4. Spurious Neighbor Discovery . . . . . . . . . . . . . 9 3.2.4. Spurious Neighbor Discovery . . . . . . . . . . . . . 9
4. Multicast protocol optimizations . . . . . . . . . . . . . . 10 4. Multicast protocol optimizations . . . . . . . . . . . . . . 10
4.1. Proxy ARP in 802.11-2012 . . . . . . . . . . . . . . . . 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 4.3. Buffering to Improve Battery Life . . . . . . . . . . . . 12
4.4. Limiting multicast buffer hardware queue depth . . . . . 12 4.4. Limiting multicast buffer hardware queue depth . . . . . 13
4.5. IPv6 support in 802.11-2012 . . . . . . . . . . . . . . . 12 4.5. IPv6 support in 802.11-2012 . . . . . . . . . . . . . . . 13
4.6. Using Unicast Instead of Multicast . . . . . . . . . . . 13 4.6. Using Unicast Instead of Multicast . . . . . . . . . . . 14
4.6.1. Overview . . . . . . . . . . . . . . . . . . . . . . 13 4.6.1. Overview . . . . . . . . . . . . . . . . . . . . . . 14
4.6.2. Layer 2 Conversion to Unicast . . . . . . . . . . . . 13 4.6.2. Layer 2 Conversion to Unicast . . . . . . . . . . . . 14
4.6.3. Directed Multicast Service (DMS) . . . . . . . . . . 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 4.7. GroupCast with Retries (GCR) . . . . . . . . . . . . . . 15
5. Operational optimizations . . . . . . . . . . . . . . . . . . 15 5. Operational optimizations . . . . . . . . . . . . . . . . . . 16
5.1. Mitigating Problems from Spurious Neighbor Discovery . . 16 5.1. 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 6. Multicast Considerations for Other Wireless Media . . . . . . 18
7. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 18 7. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 19
8. Discussion Items . . . . . . . . . . . . . . . . . . . . . . 19 8. Discussion Items . . . . . . . . . . . . . . . . . . . . . . 19
9. Security Considerations . . . . . . . . . . . . . . . . . . . 19 9. Security Considerations . . . . . . . . . . . . . . . . . . . 20
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
12. Informative References . . . . . . . . . . . . . . . . . . . 20 12. Informative References . . . . . . . . . . . . . . . . . . . 20
Appendix A. Changes in this draft between revisions 06 versus 07 23 Appendix A. Changes in this draft between revisions 06 versus 07 24
Appendix B. Changes in this draft between revisions 05 versus 06 23 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 C. Changes in this draft between revisions 04 versus 05 24
Appendix D. Changes in this draft between revisions 03 versus 04 24 Appendix D. Changes in this draft between revisions 03 versus 04 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction 1. Introduction
Well-known issues with multicast have prevented the deployment of Well-known issues with multicast have prevented the deployment of
multicast in 802.11 [dot11] and other local-area wireless multicast in 802.11 [dot11] and other local-area wireless
environments, as described in [mc-props], [mc-prob-stmt]. environments, as described in [mc-props], [mc-prob-stmt].
Performance issues have been observed when multicast packet Performance issues have been observed when multicast packet
transmissions of IETF protocols are used over IEEE 802 wireless transmissions of IETF protocols are used over IEEE 802 wireless
media. Even though enhancements for multicast transmissions have media. Even though enhancements for multicast transmissions have
been designed at both IETF and IEEE 802, incompatibilities still been designed at both IETF and IEEE 802, incompatibilities still
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lower modulation transmissions occupy the medium longer; they hamper lower modulation transmissions occupy the medium longer; they hamper
efficient transmission of traffic using higher order modulations to efficient transmission of traffic using higher order modulations to
nearby stations. For these and other reasons, IEEE 802 working nearby stations. For these and other reasons, IEEE 802 working
groups such as 802.11 have designed features to improve the groups such as 802.11 have designed features to improve the
performance of multicast transmissions at Layer 2 [ietf_802-11]. In performance of multicast transmissions at Layer 2 [ietf_802-11]. In
addition to protocol design features, certain operational and addition to protocol design features, certain operational and
configuration enhancements can ameliorate the network performance 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.
There seems to be general agreement that these problems will not be There seems to be general agreement that these problems will not be
fixed anytime soon, primarily because it's expensive to do so, and fixed anytime soon, primarily because it's expensive to do so and due
multicast is unreliable. Compared to unicast over Wi-Fi, multicast to multicast being unreliable. Compared to unicast over Wi-Fi,
is often treated as somewhat a second class citizen, even though multicast is often treated as somewhat of a second class citizen,
there are many protocols using multicast. Something needs to be even though there are many protocols using multicast. Something
provided in order to make them more reliable. IPv6 neighbor needs to be provided in order to make them more reliable. IPv6
discovery saturating the Wi-Fi link is only part of the problem. Wi- neighbor discovery saturating the Wi-Fi link is only part of the
Fi traffic classes may help. This document is intended to help make problem. Wi-Fi traffic classes may help. This document is intended
the determination about what problems should be solved by the IETF to help make the determination about what problems should be solved
and what problems should be solved by the IEEE (see Section 8). by the IETF and what problems should be solved by the IEEE (see
Section 8).
This document details various problems caused by multicast This document details various problems caused by multicast
transmission over wireless networks, including high packet error transmission over wireless networks, including high packet error
rates, no acknowledgements, and low data rate. It also explains some 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 ameliorate the effects of multicast traffic. Recommendations are
also provided to implementors about how to use and combine these also provided to implementors about how to use and combine these
enhancements. Some advice about the operational choices that can be enhancements. Some advice about the operational choices that can be
taken is also included. It is likely that this document will also be taken is also included. It is likely that this document will also be
considered relevant to designers of future IEEE wireless considered relevant to designers of future IEEE wireless
specifications. specifications.
2. Terminology 2. Terminology
This document uses the following definitions: This document uses the following definitions:
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multicast packet; generally the Access Point has to use a much lower 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 data rate at a power level high enough for even the farthest station
to receive the packet, for example as briefly mentioned in [RFC5757]. to receive the packet, for example as briefly mentioned in [RFC5757].
Consequently, the data rate of a video stream, for instance, would be Consequently, the data rate of a video stream, for instance, would be
constrained by the environmental considerations of the least reliable constrained by the environmental considerations of the least reliable
receiver associated with the Access Point. receiver associated with the Access Point.
Because more robust modulation and coding schemes (MCSs) have longer Because more robust modulation and coding schemes (MCSs) have longer
range but also lower data rate, multicast / broadcast traffic is range but also lower data rate, multicast / broadcast traffic is
generally transmitted at the slowest rate of all the connected generally transmitted at the slowest rate of all the connected
devices, also known as the basic rate. The amount of additional devices. This is also known as the basic rate. The amount of
interference depends on the specific wireless technology. In fact additional interference depends on the specific wireless technology.
backward compatibility and multi-stream implementations mean that the In fact, backward compatibility and multi-stream implementations mean
maximum unicast rates are currently up to a few Gb/s, so there can be that the maximum unicast rates are currently up to a few Gbps, so
a more than 3 orders of magnitude difference in the transmission rate there can be more than 3 orders of magnitude difference in the
between multicast / broadcast versus optimal unicast forwarding. transmission rate between multicast / broadcast versus optimal
Some techinues employed to increase spectral efficiency, such as unicast forwarding. Some techiques employed to increase spectral
spatial multiplexing in mimo systems, are not available with more efficiency, such as spatial multiplexing in mimo systems, are not
than one intended reciever; it is not the case that backwards available with more than one intended reciever; it is not the case
compatibility is the only factor responsible for lower multicast that backwards compatibility is the only factor responsible for lower
transmission rates. multicast transmission rates.
Wired multicast also affects wireless LANs when the AP extends the Wired multicast also affects wireless LANs when the AP extends the
wired segment; in that case, multicast / broadcast frames on the wired segment; in that case, multicast / broadcast frames on the
wired LAN side are copied to WLAN. Since broadcast messages are wired LAN side are copied to WLAN. Since broadcast messages are
transmitted at the most robust MCS, many large frames are sent at a transmitted at the most robust MCS, many large frames are sent at a
slow rate over the air. slow rate over the air.
3.1.3. High Interference 3.1.3. High Interference
Transmissions at a lower rate require longer occupancy of the Transmissions at a lower rate require longer occupancy of the
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3.2. Issues at Layer 3 and Above 3.2. Issues at Layer 3 and Above
This section identifies some representative IETF protocols, and This section identifies some representative IETF protocols, and
describes possible negative effects due to performance degradation describes possible negative effects due to performance degradation
when using multicast transmissions for control messages. Common uses when using multicast transmissions for control messages. Common uses
of multicast include: of multicast include:
o Control plane signaling o Control plane signaling
o Neighbor Discovery o Neighbor Discovery
o Address Resolution o Address Resolution
o Service discovery o Service Discovery
o Applications (video delivery, stock data, etc.) o Applications (video delivery, stock data, etc.)
o On-demand routing o On-demand routing
o Backbone construction o Backbone construction
o Other L3 protocols (non-IP) o Other L3 protocols (non-IP)
User Datagram Protocol (UDP) is the most common transport layer User Datagram Protocol (UDP) is the most common transport layer
protocol for multicast applications. By itself, UDP is not reliable protocol for multicast applications. By itself, UDP is not reliable
-- messages may be lost or delivered out of order. -- messages may be lost or delivered out of order.
3.2.1. IPv4 issues 3.2.1. IPv4 issues
The following list contains some representative multicast protocols The following list contains some representative multicast protocols
that are used with IPv4. that are used with IPv4.
o ARP o ARP
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service discovery protocols (e.g., for finding a printer) utilize service discovery protocols (e.g., for finding a printer) utilize
mDNS (i.e., multicast). It's often the first service that operators mDNS (i.e., multicast). It's often the first service that operators
drop. Even if multicast snooping is utilized, many devices can drop. Even if multicast snooping is utilized, many devices can
register at once and cause serious network degradation. register at once and cause serious network degradation.
3.2.2. IPv6 issues 3.2.2. IPv6 issues
IPv6 makes extensive use of multicast, including the following: IPv6 makes extensive use of multicast, including the following:
o DHCPv6 o DHCPv6
o IPv6 Neighbor Discovery Protocol (NDP) o IPv6 Neighbor Discovery Protocol (NDP) [RFC4861]
o Duplicate Address Detection (DAD) o multicast DNS (mDNS)
o Address Resolution
o Service Discovery
o Route Discovery o Route Discovery
o Decentralized Address Assignment o Decentralized Address Assignment
o Geographic routing o Geographic routing
IPv6 NDP Neighbor Solicitation (NS) messages used in DAD and Address IPv6 NDP Neighbor Solicitation (NS) messages used in Duplicate
Lookup make use of Link-Scope multicast. In contrast to IPv4, an Address Detection (DAD) and Address Lookup make use of Link-Scope
IPv6 node will typically use multiple addresses, and may change them multicast. In contrast to IPv4, an IPv6 node will typically use
often for privacy reasons. This intensifies the impact of multicast multiple addresses, and may change them often for privacy reasons.
messages that are associated to the mobility of a node. Router This intensifies the impact of multicast messages that are associated
advertisement (RA) messages are also periodically multicasted over to the mobility of a node. Router advertisement (RA) messages are
the Link. also periodically multicasted over the Link.
Neighbors may be considered lost if several consecutive Neighbor Neighbors may be considered lost if several consecutive Neighbor
Discovery packets fail. Discovery packets fail.
3.2.3. MLD issues 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 members of a multicast group that are connected to the ports of a
switch. Forwarding multicast frames into a Wi-Fi-enabled area can switch. Forwarding multicast frames into a Wi-Fi-enabled area can
use such switch support for hardware forwarding state information. use such switch support for hardware forwarding state information.
However, since IPv6 makes heavy use of multicast, each STA with an However, since IPv6 makes heavy use of multicast, each STA with an
IPv6 address will require state on the switch for several and IPv6 address will require state on the switch for several and
possibly many multicast solicited-node addresses. Multicast possibly many multicast solicited-node addresses. Multicast
addresses that do not have forwarding state installed (perhaps due to addresses that do not have forwarding state installed (perhaps due to
hardware memory limitations on the switch) cause frames to be flooded 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 3.2.4. Spurious Neighbor Discovery
On the Internet there is a "background radiation" of scanning traffic On the Internet there is a "background radiation" of scanning traffic
(people scanning for vulnerable machines) and backscatter (responses (people scanning for vulnerable machines) and backscatter (responses
from spoofed traffic, etc). This means that routers very often from spoofed traffic, etc). This means that routers very often
receive packets destined for IP addresses regardless of whether those 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 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, 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 and caches it; then traffic can be delivered to the host. When the
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populate the ARP cache, and the next time there is traffic for that populate the ARP cache, and the next time there is traffic for that
IP address the router will rebroadcast the ARP requests. IP address the router will rebroadcast the ARP requests.
The rate of these ARP requests is proportional to the size of the The rate of these ARP requests is proportional to the size of the
subnets, the rate of scanning and backscatter, and how long the subnets, the rate of scanning and backscatter, and how long the
router keeps state on non-responding ARPs. As it turns out, this router keeps state on non-responding ARPs. As it turns out, this
rate is inversely proportional to how occupied the subnet is (valid rate is inversely proportional to how occupied the subnet is (valid
ARPs end up in a cache, stopping the broadcasting; unused IPs never ARPs end up in a cache, stopping the broadcasting; unused IPs never
respond, and so cause more broadcasts). Depending on the address respond, and so cause more broadcasts). Depending on the address
space in use, the time of day, how occupied the subnet is, and other 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 unknown factors, thousands of broadcasts per second have been
observed, for instance at the NOCs during IETF face-to-face meetings. 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, On a wired network, there is not a huge difference between unicast,
multicast and broadcast traffic. Due to hardware filtering (see, multicast and broadcast traffic. Due to hardware filtering (see,
e.g., [Deri-2010]), inadvertently flooded traffic (or excessive e.g., [Deri-2010]), inadvertently flooded traffic (or excessive
ethernet multicast) on wired networks can be quite a bit less costly, ethernet multicast) on wired networks can be quite a bit less costly,
compared to wireless cases where sleeping devices have to wake up to compared to wireless cases where sleeping devices have to wake up to
process packets. Wired Ethernets tend to be switched networks, process packets. Wired Ethernets tend to be switched networks,
further reducing interference from multicast. There is effectively further reducing interference from multicast. There is effectively
no collision / scheduling problem except at extremely high port no collision / scheduling problem except at extremely high port
utilizations. utilizations.
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4.2. IPv6 Address Registration and Proxy Neighbor Discovery 4.2. IPv6 Address Registration and Proxy Neighbor Discovery
As used in this section, a Low-Power Wireless Personal Area Network As used in this section, a Low-Power Wireless Personal Area Network
(6LoWPAN) denotes a low power lossy network (LLN) that supports (6LoWPAN) denotes a low power lossy network (LLN) that supports
6LoWPAN Header Compression (HC) [RFC6282]. A 6TiSCH network 6LoWPAN Header Compression (HC) [RFC6282]. A 6TiSCH network
[I-D.ietf-6tisch-architecture] is an example of a 6LowPAN. In order [I-D.ietf-6tisch-architecture] is an example of a 6LowPAN. In order
to control the use of IPv6 multicast over 6LoWPANs, the 6LoWPAN to control the use of IPv6 multicast over 6LoWPANs, the 6LoWPAN
Neighbor Discovery (6LoWPAN ND) [RFC6775] standard defines an address Neighbor Discovery (6LoWPAN ND) [RFC6775] standard defines an address
registration mechanism that relies on a central registry to assess registration mechanism that relies on a central registry to assess
address uniqueness, as a substitute to the inefficient Duplicate address uniqueness, as a substitute to the inefficient DAD mechanism
Address Detection (DAD) mechanism found in the mainstream IPv6 found in the mainstream IPv6 Neighbor Discovery Protocol (NDP)
Neighbor Discovery Protocol (NDP) [RFC4861][RFC4862]. [RFC4861][RFC4862].
The 6lo Working Group has specified an update [RFC8505] to RFC6775. The 6lo Working Group has specified an update [RFC8505] to RFC6775.
Wireless devices can register their address to a Backbone Router Wireless devices can register their address to a Backbone Router
[I-D.ietf-6lo-backbone-router], which proxies for the registered [I-D.ietf-6lo-backbone-router], which proxies for the registered
addresses with the IPv6 NDP running on a high speed aggregating addresses with the IPv6 NDP running on a high speed aggregating
backbone. The update also enables a proxy registration mechanism on backbone. The update also enables a proxy registration mechanism on
behalf of the registered node, e.g. by a 6LoWPAN router to which the behalf of the registered node, e.g. by a 6LoWPAN router to which the
mobile node is attached. mobile node is attached.
The general idea behind the backbone router concept is that broadcast The general idea behind the backbone router concept is that broadcast
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reception. If an AP, for instance, expresses a DTIM (Delivery reception. If an AP, for instance, expresses a DTIM (Delivery
Traffic Indication Message) of 3 then the AP will send a multicast Traffic Indication Message) of 3 then the AP will send a multicast
packet every 3 packets. In fact, when any single wireless STA packet every 3 packets. In fact, when any single wireless STA
associated with an access point has 802.11 power-save mode enabled, associated with an access point has 802.11 power-save mode enabled,
the access point buffers all multicast frames and sends them only the access point buffers all multicast frames and sends them only
after the next DTIM beacon. after the next DTIM beacon.
In practice, most AP's will send a multicast every 30 packets. For 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 unicast the AP could send a TIM (Traffic Indication Message), but for
multicast the AP sends a broadcast to everyone. DTIM does power 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 management but STAs can choose whether or not to wake up and whether
whether or not to drop the packet. Unfortunately, without proper or not to drop the packet. Unfortunately, without proper
administrative control, such STAs may be unable to determine why administrative control, such STAs may be unable to determine why
their multicast operations do not work. their multicast operations do not work.
4.4. Limiting multicast buffer hardware queue depth 4.4. Limiting multicast buffer hardware queue depth
The CAB (Content after Beacon) queue is used for beacon-triggered The CAB (Content after Beacon) queue is used for beacon-triggered
transmission of buffered multicast frames. If lots of multicast transmission of buffered multicast frames. If lots of multicast
frames were buffered, and this queue fills up, it drowns out all frames were buffered, and this queue fills up, it drowns out all
regular traffic. To limit the damage that buffered traffic can do, regular traffic. To limit the damage that buffered traffic can do,
some drivers limit the amount of queued multicast data to a fraction some drivers limit the amount of queued multicast data to a fraction
of the beacon_interval. An example of this is [CAB]. of the beacon_interval. An example of this is [CAB].
4.5. IPv6 support in 802.11-2012 4.5. IPv6 support in 802.11-2012
IPv6 uses Neighbor Discovery Protocol (NDP) instead of ARP. Every IPv6 uses NDP instead of ARP. Every IPv6 node subscribes to a
IPv6 node subscribes to a special multicast address for this purpose. special multicast address for this purpose.
Here is the specification language from clause 10.23.13 of Here is the specification language from clause 10.23.13 of
[dot11-proxyarp]: [dot11-proxyarp]:
"When an IPv6 address is being resolved, the Proxy Neighbor "When an IPv6 address is being resolved, the Proxy Neighbor
Discovery service shall respond with a Neighbor Advertisement Discovery service shall respond with a Neighbor Advertisement
message [...] on behalf of an associated STA to an [ICMPv6] message [...] on behalf of an associated STA to an [ICMPv6]
Neighbor Solicitation message [...]. When MAC address mappings Neighbor Solicitation message [...]. When MAC address mappings
change, the AP may send unsolicited Neighbor Advertisement change, the AP may send unsolicited Neighbor Advertisement
Messages on behalf of a STA." Messages on behalf of a STA."
skipping to change at page 14, line 39 skipping to change at page 15, line 23
4.6.4. Automatic Multicast Tunneling (AMT) 4.6.4. Automatic Multicast Tunneling (AMT)
AMT[RFC7450] provides a method to tunnel multicast IP packets inside AMT[RFC7450] provides a method to tunnel multicast IP packets inside
unicast IP packets over network links that only support unicast. unicast IP packets over network links that only support unicast.
When an operating system or application running on an STA has an AMT When an operating system or application running on an STA has an AMT
gateway capability integrated, it's possible to use unicast to 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 traverse the Wi-Fi link by deploying an AMT relay in the non-Wi-Fi
portion of the network connected to the AP. 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 relays for this purpose make the relays locally discoverable with the
following methods, as described in following methods, as described in
[I-D.ietf-mboned-driad-amt-discovery]: [I-D.ietf-mboned-driad-amt-discovery]:
o DNS-SD [RFC6763] o DNS-SD [RFC6763]
o the well-known IP addresses from Section 7 of [RFC7450] o the well-known IP addresses from Section 7 of [RFC7450]
An AMT gateway that implements multiple standard discovery methods is An AMT gateway that implements multiple standard discovery methods is
more likely to discover the local multicast-capable network, instead 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) 4.7. GroupCast with Retries (GCR)
GCR (defined in [dot11aa]) provides greater reliability by using GCR (defined in [dot11aa]) provides greater reliability by using
either unsolicited retries or a block acknowledgement mechanism. GCR either unsolicited retries or a block acknowledgement mechanism. GCR
increases probability of broadcast frame reception success, but still increases probability of broadcast frame reception success, but still
does not guarantee success. does not guarantee success.
For the block acknowledgement mechanism, the AP transmits each group For the block acknowledgement mechanism, the AP transmits each group
addressed frame as conventional group addressed transmission. addressed frame as conventional group addressed transmission.
Retransmissions are group addressed, but hidden from non-11aa STAs. Retransmissions are group addressed, but hidden from non-11aa STAs.
A directed block acknowledgement scheme is used to harvest reception A directed block acknowledgement scheme is used to harvest reception
status from receivers; retransmissions are based upon these status from receivers; retransmissions are based upon these
responses. responses.
GCR is suitable for all group sizes including medium to large groups. 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 As the number of devices in the group increases, GCR can send block
acknowledgement requests to only a small subset of the group. GCR 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 GCR may introduce unacceptable latency. After sending a group of
data frames to the group, the AP has do the following: data frames to the group, the AP has do the following:
o unicast a Block Ack Request (BAR) to a subset of members. o unicast a Block Ack Request (BAR) to a subset of members.
o wait for the corresponding Block Ack (BA). o wait for the corresponding Block Ack (BA).
o retransmit any missed frames. o retransmit any missed frames.
o resume other operations that may have been delayed. o resume other operations that may have been delayed.
This latency may not be acceptable for some traffic. This latency may not be acceptable for some traffic.
skipping to change at page 16, line 34 skipping to change at page 17, line 14
population rate versus retires, etc.) and sometimes the daemons population rate versus retires, etc.) and sometimes the daemons
just seem to stop, requiring a restart of the daemon and just seem to stop, requiring a restart of the daemon and
causing disruption. causing disruption.
Router mitigations Router mitigations
Some routers (often those based on Linux) implement a "negative Some routers (often those based on Linux) implement a "negative
ARP cache" daemon. Simply put, if the router does not see a ARP cache" daemon. Simply put, if the router does not see a
reply to an ARP it can be configured to cache this information reply to an ARP it can be configured to cache this information
for some interval. Unfortunately, the core routers in use for some interval. Unfortunately, the core routers in use
often do not support this. When a host connects to network and often do not support this. When a host connects to a network
gets an IP address, it will ARP for its default gateway (the and gets an IP address, it will ARP for its default gateway
router). The router will update its cache with the IP to host (the router). The router will update its cache with the IP to
MAC mapping learnt from the request (passive ARP learning). host MAC mapping learned from the request (passive ARP
learning).
Firewall unused space Firewall unused space
The distribution of users on wireless networks / subnets The distribution of users on wireless networks / subnets
changes from one IETF meeting to the next (e.g SSIDs are changes from one IETF meeting to the next (e.g SSIDs are
renamed, some SSIDs lose favor, etc). This makes utilization renamed, some SSIDs lose favor, etc). This makes utilization
for particular SSIDs difficult to predict ahead of time, but for particular SSIDs difficult to predict ahead of time, but
usage can be monitored as attendees use the different networks. usage can be monitored as attendees use the different networks.
Configuring multiple DHCP pools per subnet, and enabling them Configuring multiple DHCP pools per subnet, and enabling them
sequentially, can create a large subnet, from which only sequentially, can create a large subnet, from which only
skipping to change at page 19, line 38 skipping to change at page 20, line 15
faster (2 orders of magnitude) and much more reliable (L2 ARQ). faster (2 orders of magnitude) and much more reliable (L2 ARQ).
9. Security Considerations 9. Security Considerations
This document does not introduce or modify any security mechanisms. This document does not introduce or modify any security mechanisms.
As noted in [group_key], the unreliable nature of multicast As noted in [group_key], the unreliable nature of multicast
transmission over wireless media can cause subtle problems with transmission over wireless media can cause subtle problems with
multicast group key management and updates. Quoting from that multicast group key management and updates. Quoting from that
website, "... most clients are able to get connected and surf the website, "... most clients are able to get connected and surf the
web, check email, etc. even when FromDS multicasts are broken. So a web, check email, etc. even when From DS multicasts are broken. So a
lot of people don't realize they have multicast problems on their lot of people don't realize they have multicast problems on their
network..." network..."
10. IANA Considerations 10. IANA Considerations
This document does not request any IANA actions. This document does not request any IANA actions.
11. Acknowledgements 11. Acknowledgements
This document has benefitted from discussions with the following This document has benefitted from discussions with the following
skipping to change at page 20, line 40 skipping to change at page 21, line 23
exchange between systems Local and metropolitan area exchange between systems Local and metropolitan area
networks--Specific requirements - Part 11: Wireless LAN networks--Specific requirements - Part 11: Wireless LAN
Medium Access Control (MAC) and Physical Layer (PHY) Medium Access Control (MAC) and Physical Layer (PHY)
Specification (includes 802.11v amendment)", March 2016, Specification (includes 802.11v amendment)", March 2016,
<http://standards.ieee.org/findstds/ <http://standards.ieee.org/findstds/
standard/802.11-2016.html>. standard/802.11-2016.html>.
[dot11-proxyarp] [dot11-proxyarp]
Hiertz, G., Mestanov, F., and B. Hart, "Proxy ARP in Hiertz, G., Mestanov, F., and B. Hart, "Proxy ARP in
802.11ax", September 2015, 802.11ax", September 2015,
<https://mentor.ieee.org/802.11/ <https://mentor.ieee.org/802.11/dcn/15/11-15-1015-01-00ax-
dcn/15/11-15-1015-01-00ax-proxy-arp-in-802-11ax.pptx>. proxy-arp-in-802-11ax.pptx>.
[dot11aa] "IEEE 802 Wireless", "Part 11: Wireless LAN Medium Access [dot11aa] "IEEE 802 Wireless", "Part 11: Wireless LAN Medium Access
Control (MAC) and Physical Layer (PHY) Specifications Control (MAC) and Physical Layer (PHY) Specifications
Amendment 2: MAC Enhancements for Robust Audio Video Amendment 2: MAC Enhancements for Robust Audio Video
Streaming", March 2012, Streaming", March 2012,
<http://standards.ieee.org/findstds/ <http://standards.ieee.org/findstds/standard/802.11aa-
standard/802.11aa-2012.pdf>. 2012.pdf>.
[group_key] [group_key]
Spiff, ""Why do some WiFi routers block multicast packets Spiff, ""Why do some WiFi routers block multicast packets
going from wired to wireless?"", Jan 2017, going from wired to wireless?"", Jan 2017,
<https://superuser.com/questions/730288/why-do-some-wifi- <https://superuser.com/questions/730288/why-do-some-wifi-
routers-block-multicast-packets-going-from-wired-to- routers-block-multicast-packets-going-from-wired-to-
wireless>. wireless>.
[I-D.ietf-6lo-backbone-router] [I-D.ietf-6lo-backbone-router]
Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6 Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6
Backbone Router", draft-ietf-6lo-backbone-router-11 (work Backbone Router", draft-ietf-6lo-backbone-router-13 (work
in progress), February 2019. in progress), September 2019.
[I-D.ietf-6tisch-architecture] [I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-24 (work of IEEE 802.15.4", draft-ietf-6tisch-architecture-26 (work
in progress), July 2019. in progress), August 2019.
[I-D.ietf-mboned-driad-amt-discovery] [I-D.ietf-mboned-driad-amt-discovery]
Holland, J., "DNS Reverse IP AMT Discovery", draft-ietf- Holland, J., "DNS Reverse IP AMT Discovery", draft-ietf-
mboned-driad-amt-discovery-08 (work in progress), June mboned-driad-amt-discovery-08 (work in progress), June
2019. 2019.
[ietf_802-11] [ietf_802-11]
Stanley, D., "IEEE 802.11 multicast capabilities", Nov Stanley, D., "IEEE 802.11 multicast capabilities", Nov
2015, <https://mentor.ieee.org/802.11/ 2015, <https://mentor.ieee.org/802.11/
dcn/15/11-15-1261-03-0arc-multicast-performance- dcn/15/11-15-1261-03-0arc-multicast-performance-
skipping to change at page 22, line 12 skipping to change at page 22, line 42
dcn/15/11-15-1161-02-0arc-802-11-multicast- dcn/15/11-15-1161-02-0arc-802-11-multicast-
properties.ppt>. properties.ppt>.
[Oliva2013] [Oliva2013]
de la Oliva, A., Serrano, P., Salvador, P., and A. Banchs, de la Oliva, A., Serrano, P., Salvador, P., and A. Banchs,
"Performance evaluation of the IEEE 802.11aa multicast "Performance evaluation of the IEEE 802.11aa multicast
mechanisms for video streaming", 2013 IEEE 14th mechanisms for video streaming", 2013 IEEE 14th
International Symposium on "A World of Wireless, Mobile International Symposium on "A World of Wireless, Mobile
and Multimedia Networks" (WoWMoM) pp. 1-9, June 2013. 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,
<https://www.rfc-editor.org/info/rfc2461>.
[RFC4541] Christensen, M., Kimball, K., and F. Solensky, [RFC4541] Christensen, M., Kimball, K., and F. Solensky,
"Considerations for Internet Group Management Protocol "Considerations for Internet Group Management Protocol
(IGMP) and Multicast Listener Discovery (MLD) Snooping (IGMP) and Multicast Listener Discovery (MLD) Snooping
Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006,
<https://www.rfc-editor.org/info/rfc4541>. <https://www.rfc-editor.org/info/rfc4541>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007, DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>. <https://www.rfc-editor.org/info/rfc4861>.
skipping to change at page 23, line 28 skipping to change at page 24, line 18
Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018,
<https://www.rfc-editor.org/info/rfc8505>. <https://www.rfc-editor.org/info/rfc8505>.
[Tramarin2017] [Tramarin2017]
Tramarin, F., Vitturi, S., and M. Luvisotto, "IEEE 802.11n Tramarin, F., Vitturi, S., and M. Luvisotto, "IEEE 802.11n
for Distributed Measurement Systems", 2017 IEEE for Distributed Measurement Systems", 2017 IEEE
International Instrumentation and Measurement Technology International Instrumentation and Measurement Technology
Conference (I2MTC) pp. 1-6, May 2017. Conference (I2MTC) pp. 1-6, May 2017.
[uli] Kinney, P., "LLC Proposal for 802.15.4", Nov 2015, [uli] Kinney, P., "LLC Proposal for 802.15.4", Nov 2015,
<https://mentor.ieee.org/802.15/ <https://mentor.ieee.org/802.15/dcn/15/15-15-0521-01-wng0-
dcn/15/15-15-0521-01-wng0-llc-proposal-for-802-15-4.pptx>. llc-proposal-for-802-15-4.pptx>.
Appendix A. Changes in this draft between revisions 06 versus 07 Appendix A. Changes in this draft between revisions 06 versus 07
This section lists the changes between revisions ...-06.txt and This section lists the changes between revisions ...-06.txt and
...-07.txt of draft-ietf-mboned-ieee802-mcast-problems. ...-07.txt of draft-ietf-mboned-ieee802-mcast-problems.
o Improved wording in section describing ARPsponge. o Improved wording in section describing ARPsponge.
o Removed DRIAD as a discovery mechanism for multicast relays. o Removed DRIAD as a discovery mechanism for multicast relays.
o Updated bibliographic citations, repaired broken URLs as needed. o Updated bibliographic citations, repaired broken URLs as needed.
o More editorial improvements and grammatical corrections. o More editorial improvements and grammatical corrections.
 End of changes. 38 change blocks. 
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