draft-ietf-v6ops-reducing-ra-energy-consumption-03.txt   rfc7772.txt 
IPv6 Operations A. Yourtchenko Internet Engineering Task Force (IETF) A. Yourtchenko
Internet-Draft Cisco Request for Comments: 7772 Cisco
Intended status: Best Current Practice L. Colitti BCP: 202 L. Colitti
Expires: May 8, 2016 Google Category: Best Current Practice Google
November 5, 2015 ISSN: 2070-1721 February 2016
Reducing energy consumption of Router Advertisements Reducing Energy Consumption of Router Advertisements
draft-ietf-v6ops-reducing-ra-energy-consumption-03
Abstract Abstract
Frequent Router Advertisement messages can severely impact host power Frequent Router Advertisement messages can severely impact host power
consumption. This document recommends operational practices to avoid consumption. This document recommends operational practices to avoid
such impact. such impact.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This memo documents an Internet Best Current Practice.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
BCPs is available in Section 2 of RFC 5741.
This Internet-Draft will expire on May 8, 2016. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7772.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Problem scenarios . . . . . . . . . . . . . . . . . . . . . . 2 2. Problem Scenarios . . . . . . . . . . . . . . . . . . . . . . 2
2.1. Solicited multicast RAs on large networks . . . . . . . . 2 2.1. Solicited Multicast RAs on Large Networks . . . . . . . . 2
2.2. Frequent periodic Router Advertisements . . . . . . . . . 2 2.2. Frequent Periodic Router Advertisements . . . . . . . . . 3
3. Consequences . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Consequences . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Router Advertisement frequency . . . . . . . . . . . . . . . 3 4. Router Advertisement Frequency . . . . . . . . . . . . . . . 3
5. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 4 5. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Network-side recommendations . . . . . . . . . . . . . . 4 5.1. Network-Side Recommendations . . . . . . . . . . . . . . 4
5.2. Device-side recommendations . . . . . . . . . . . . . . . 5 5.2. Device-Side Recommendations . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . 5 7.1. Normative References . . . . . . . . . . . . . . . . . . 5
9. Normative References . . . . . . . . . . . . . . . . . . . . 5 7.2. Informative References . . . . . . . . . . . . . . . . . 6
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction 1. Introduction
Routing information is communicated to IPv6 hosts by Router Routing information is communicated to IPv6 hosts by Router
Advertisement (RA) messages [RFC4861]. If these messages are too Advertisement (RA) messages [RFC4861]. If these messages are sent
frequent, they can severely impact power consumption on battery- too frequently, they can severely impact power consumption on
powered hosts. battery-powered hosts.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Problem scenarios 2. Problem Scenarios
2.1. Solicited multicast RAs on large networks 2.1. Solicited Multicast RAs on Large Networks
On links with a large number of battery-powered devices, sending On links with a large number of battery-powered devices, sending
solicited Router Advertisements multicast can severely impact host solicited multicast Router Advertisements can severely impact host
power consumption. This is because every time a device joins the power consumption. This is because every time a device joins the
network, all devices on the network receive a multicast Router network, all devices on the network receive a multicast Router
Advertisement. In the worst case, if devices are continually joining Advertisement. In the worst case, if devices are continually joining
and leaving the network, and the network is large enough, then all and leaving the network, and the network is large enough, then all
devices on the network will receive solicited Router Advertisements devices on the network will receive solicited Router Advertisements
at the maximum rate specified by section 6.2.6 of [RFC4861], which is at the maximum rate specified by Section 6.2.6 of [RFC4861], which is
one every 3 seconds. one every 3 seconds.
2.2. Frequent periodic Router Advertisements 2.2. Frequent Periodic Router Advertisements
Some networks send periodic multicast Router Advertisements very Some networks send periodic multicast Router Advertisements very
frequently (e.g., once every few seconds). This may be due to a frequently (e.g., once every few seconds). This may be due to a
desire to minimize customer impact of network renumbering events, desire to minimize customer impact of network renumbering events,
which in some large residential networks occur relatively frequently. which in some large residential networks occur relatively frequently.
In the presence of hosts that ignore RAs or even all IPv6 packets In the presence of hosts that ignore RAs or even all IPv6 packets
when in sleep mode, such networks may see a need to send RAs when in sleep mode, such networks may see a need to send RAs
frequently in order to avoid leaving devices with non-functional IPv6 frequently in order to avoid leaving devices with non-functional IPv6
configurations for extended periods of time. Unfortunately, this has configurations for extended periods of time. Unfortunately, this has
severe impact on battery life. severe impact on battery life.
3. Consequences 3. Consequences
Observed reactions to frequent Router Advertisement messages by Observed effects of frequently sending Router Advertisement messages
battery-powered devices include: to battery-powered devices include:
o Some hosts simply experience bad battery life on these networks o Some hosts simply experience bad battery life on these networks
and otherwise operate normally. This is frustrating for users of and otherwise operate normally. This is frustrating for users of
these networks. these networks.
o Some hosts react by dropping all Router Advertisement messages o Some hosts react by dropping all Router Advertisement messages
when in power saving mode on any network, e.g., when in power-saving mode on any network, e.g.,
<https://code.google.com/p/android/issues/detail?id=32662>. This <https://code.google.com/p/android/issues/detail?id=32662>. This
causes devices to lose connectivity when in power-saving mode, causes devices to lose connectivity when in power-saving mode,
potentially disrupting background network communications, because potentially disrupting background network communications, because
the device is no longer able to send packets or acknowledge the device is no longer able to send packets or acknowledge
received traffic. received traffic.
o Some hosts react by dropping *all* IPv6 packets when in power o Some hosts react by dropping *all* IPv6 packets when in power-
saving mode, <http://www.gossamer-threads.com/lists/nsp/ saving mode, <http://www.gossamer-threads.com/lists/nsp/
ipv6/54641>. This disrupts network communications. ipv6/54641>. This disrupts network communications.
Compounding the problem, when dealing with devices that drop Router Compounding the problem, when dealing with devices that drop Router
Advertisements when in power saving mode, some network administrators Advertisements when in power saving mode, some network administrators
work around the problem by sending RAs even more frequently. This work around the problem by sending RAs even more frequently. This
causes devices to engage in even more aggressive filtering. causes devices to engage in even more aggressive filtering.
4. Router Advertisement frequency 4. Router Advertisement Frequency
The appropriate frequency of periodic RAs depends on how constrained The appropriate frequency of periodic RAs depends on how constrained
the network devices are. the network devices are.
o Laptop-class devices will likely experience no noticeable battery o Laptop-class devices will likely experience no noticeable battery-
life impact even if RAs are sent every few seconds. life impact, even if RAs are sent every few seconds.
o Tablets, phones, and watches experience it more noticeably. At o Tablets, phones, and watches experience it more noticeably. At
the time of writing, current-generation devices might consume on the time of writing, current-generation devices might consume on
the order of 5 mA when the main processor is asleep. Upon the order of 5 mA when the main processor is asleep. Upon
receiving a packet, they might consume on the order of 200 mA for receiving a packet, they might consume on the order of 200 mA for
250ms, as the packet causes the main processor to wake up, process 250 ms, as the packet causes the main processor to wake up,
the RA, attend to other pending tasks, and then go back to sleep process the RA, attend to other pending tasks, and then go back to
again. Thus, on such devices the cost of receiving one RA will be sleep. Thus, on such devices, the cost of receiving one RA will
approximately 0.014mAh. be approximately 0.014 mAh.
In order to limit the amount of power used to receive Router In order to limit the amount of power used to receive Router
Advertisements to, say, 2% of idle power (i.e., to impact idle Advertisements to, say, 2% of idle power (i.e., to impact idle
battery life by no more than 2%), the average power budget for battery life by no more than 2%), the average power budget for
receiving RAs must be no more than 0.1mA, or approximately 7 RAs receiving RAs must be no more than 0.1 mA, or approximately 7 RAs
per hour. Due to background multicast loss and the tendency of per hour. Due to background multicast loss and the tendency of
current devices to rate-limit multicast when asleep, many of these current devices to rate-limit multicast when asleep, many of these
RAs might not reach the device. Thus the minimum lifetimes for RA RAs might not reach the device. Thus, the minimum lifetimes for
configuration parameters such as default router lifetime might RA configuration parameters such as default router lifetime might
reasonably be 5-10 times the RA period, or roughly 45-90 minutes. reasonably be 5-10 times the RA period, or roughly 45-90 minutes.
An idle time impact of 2% relative to measured idle current is An impact of 2% relative to measured idle current is negligible,
negligible, since on this sort of device average power consumption since on this sort of device average power consumption is
is typically much higher than idle power consumption. typically much higher than idle power consumption.
o Specialized devices in non-general-purpose networks such as sensor o Specialized devices in non-general-purpose networks such as sensor
networks might have tighter requirements. In these environments, networks might have tighter requirements. In these environments,
even longer RA intervals might be appropriate. even longer RA intervals might be appropriate.
5. Recommendations 5. Recommendations
5.1. Network-side recommendations 5.1. Network-Side Recommendations
1. Router manufacturers SHOULD allow network administrators to 1. Router manufacturers SHOULD allow network administrators to
configure the routers to respond to Router Solicitations with configure the routers to respond to Router Solicitations with
unicast Router Advertisements if: unicast Router Advertisements if:
* The Router Solicitation's source address is not the * The Router Solicitation's source address is not the
unspecified address, and: unspecified address, and:
* The solicitation contains a valid Source Link-Layer Address * The solicitation contains a valid Source Link-Layer Address
option. option.
2. Administrators of networks that serve large numbers (tens or 2. Administrators of networks that serve large numbers (tens or
hundreds) of battery-powered devices SHOULD enable this hundreds) of battery-powered devices SHOULD enable this behavior.
behaviour.
3. Networks that serve battery-powered devices SHOULD NOT send 3. Networks that serve battery-powered devices SHOULD NOT send
multicast RAs too frequently (see section Section 4) unless the multicast RAs too frequently (see Section 4) unless the
information in the RA packet has substantially changed. If there information in the RA packet has substantially changed. If there
is a desire to ensure that hosts pick up configuration changes is a desire to ensure that hosts pick up configuration changes
quickly, those networks MAY send frequent Router Advertisements quickly, those networks MAY send frequent Router Advertisements
for a limited period of time (e.g., not more than one minute) for a limited period of time (e.g., not more than one minute)
immediately after a configuration change. immediately after a configuration change.
No protocol changes are required. Responding to Router Solicitations No protocol changes are required. Responding to Router Solicitations
with unicast Router Advertisements is already allowed by section with unicast Router Advertisements is already allowed by Section
6.2.6 of [RFC4861], and Router Advertisement intervals are already 6.2.6 of [RFC4861], and Router Advertisement intervals are already
configurable by the administrator to a wide range of values. configurable by the administrator to a wide range of values.
5.2. Device-side recommendations 5.2. Device-Side Recommendations
1. Maintaining IPv6 connectivity requires that hosts be able to 1. Maintaining IPv6 connectivity requires that hosts be able to
receive periodic multicast RAs [RFC4861] Therefore, hosts that receive periodic multicast RAs [RFC4861]. Therefore, hosts that
process unicast packets sent while they are asleep MUST also process unicast packets sent while they are asleep MUST also
process multicast RAs sent while they are asleep. Battery- process multicast RAs sent while they are asleep. Battery-
powered hosts MAY rate-limit identical RAs if they are sent too powered hosts MAY rate-limit identical RAs if they are sent too
frequently. frequently.
2. Battery-powered devices that do not intend to maintain IPv6 2. Battery-powered devices that do not intend to maintain IPv6
connectivity while asleep SHOULD either disconnect from the connectivity while asleep SHOULD either disconnect from the
network, abandoning all IPv6 configuration on that network, or network, abandoning all IPv6 configuration on that network, or
perform DNAv6 procedures [RFC6059] when waking up. perform Detecting Network Attachment in IPv6 (DNAv6) procedures
[RFC6059] when waking up.
6. Acknowledgements
The authors wish to thank Steven Barth, Frank Bulk, David Farmer,
Igor Gashinsky, Ray Hunter, Erik Kline, Erik Nordmark, Alexandru
Petrescu, Libor Polcak, Mark Smith, Jinmei Tatuya and James Woodyatt
for feedback and helpful suggestions.
7. IANA Considerations
None.
8. Security Considerations 6. Security Considerations
Misconfigured or malicious hosts sending rogue Router Advertisements Misconfigured or malicious hosts sending rogue Router Advertisements
[RFC6104] can also severely impact power consumption on battery- [RFC6104] can also severely impact power consumption on battery-
powered hosts if they send a significant number of such messages. powered hosts if they send a significant number of such messages.
Any IPv6 network where there is potential for misconfigured or Any IPv6 network where there is potential for misconfigured or
malicious hosts should take appropriate countermeasures to mitigate malicious hosts should take appropriate countermeasures to mitigate
the problem. the problem.
9. Normative References 7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ Requirement Levels", BCP 14, RFC 2119,
RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[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,
<http://www.rfc-editor.org/info/rfc4861>. <http://www.rfc-editor.org/info/rfc4861>.
[RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for [RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for
Detecting Network Attachment in IPv6", RFC 6059, DOI Detecting Network Attachment in IPv6", RFC 6059,
10.17487/RFC6059, November 2010, DOI 10.17487/RFC6059, November 2010,
<http://www.rfc-editor.org/info/rfc6059>. <http://www.rfc-editor.org/info/rfc6059>.
7.2. Informative References
[RFC6104] Chown, T. and S. Venaas, "Rogue IPv6 Router Advertisement
Problem Statement", RFC 6104, DOI 10.17487/RFC6104,
February 2011, <http://www.rfc-editor.org/info/rfc6104>.
Acknowledgements
The authors wish to thank Steven Barth, Frank Bulk, David Farmer,
Igor Gashinsky, Ray Hunter, Erik Kline, Erik Nordmark, Alexandru
Petrescu, Libor Polcak, Mark Smith, Jinmei Tatuya, and James Woodyatt
for feedback and helpful suggestions.
Authors' Addresses Authors' Addresses
Andrew Yourtchenko Andrew Yourtchenko
Cisco Cisco
7a de Kleetlaan 7a de Kleetlaan
Diegem, 1831 Diegem, 1831
Belgium Belgium
Phone: +32 2 704 5494 Phone: +32 2 704 5494
Email: ayourtch@cisco.com Email: ayourtch@cisco.com
Lorenzo Colitti Lorenzo Colitti
Google Google
Roppongi 6-10-1 Roppongi 6-10-1
Minato, Tokyo 106-6126 Minato, Tokyo 106-6126
JP Japan
Email: lorenzo@google.com Email: lorenzo@google.com
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