Internet DRAFT - draft-ietf-v6ops-reducing-ra-energy-consumption
draft-ietf-v6ops-reducing-ra-energy-consumption
IPv6 Operations A. Yourtchenko
Internet-Draft Cisco
Intended status: Best Current Practice L. Colitti
Expires: May 8, 2016 Google
November 5, 2015
Reducing energy consumption of Router Advertisements
draft-ietf-v6ops-reducing-ra-energy-consumption-03
Abstract
Frequent Router Advertisement messages can severely impact host power
consumption. This document recommends operational practices to avoid
such impact.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on May 8, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Problem scenarios . . . . . . . . . . . . . . . . . . . . . . 2
2.1. Solicited multicast RAs on large networks . . . . . . . . 2
2.2. Frequent periodic Router Advertisements . . . . . . . . . 2
3. Consequences . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Router Advertisement frequency . . . . . . . . . . . . . . . 3
5. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Network-side recommendations . . . . . . . . . . . . . . 4
5.2. Device-side recommendations . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . 5
9. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Routing information is communicated to IPv6 hosts by Router
Advertisement (RA) messages [RFC4861]. If these messages are too
frequent, they can severely impact power consumption on battery-
powered hosts.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Problem scenarios
2.1. Solicited multicast RAs on large networks
On links with a large number of battery-powered devices, sending
solicited Router Advertisements multicast can severely impact host
power consumption. This is because every time a device joins the
network, all devices on the network receive a multicast Router
Advertisement. In the worst case, if devices are continually joining
and leaving the network, and the network is large enough, then all
devices on the network will receive solicited Router Advertisements
at the maximum rate specified by section 6.2.6 of [RFC4861], which is
one every 3 seconds.
2.2. Frequent periodic Router Advertisements
Some networks send periodic multicast Router Advertisements very
frequently (e.g., once every few seconds). This may be due to a
desire to minimize customer impact of network renumbering events,
which in some large residential networks occur relatively frequently.
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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
frequently in order to avoid leaving devices with non-functional IPv6
configurations for extended periods of time. Unfortunately, this has
severe impact on battery life.
3. Consequences
Observed reactions to frequent Router Advertisement messages by
battery-powered devices include:
o Some hosts simply experience bad battery life on these networks
and otherwise operate normally. This is frustrating for users of
these networks.
o Some hosts react by dropping all Router Advertisement messages
when in power saving mode on any network, e.g.,
<https://code.google.com/p/android/issues/detail?id=32662>. This
causes devices to lose connectivity when in power-saving mode,
potentially disrupting background network communications, because
the device is no longer able to send packets or acknowledge
received traffic.
o Some hosts react by dropping *all* IPv6 packets when in power
saving mode, <http://www.gossamer-threads.com/lists/nsp/
ipv6/54641>. This disrupts network communications.
Compounding the problem, when dealing with devices that drop Router
Advertisements when in power saving mode, some network administrators
work around the problem by sending RAs even more frequently. This
causes devices to engage in even more aggressive filtering.
4. Router Advertisement frequency
The appropriate frequency of periodic RAs depends on how constrained
the network devices are.
o Laptop-class devices will likely experience no noticeable battery
life impact even if RAs are sent every few seconds.
o Tablets, phones, and watches experience it more noticeably. At
the time of writing, current-generation devices might consume on
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
250ms, as the packet causes the main processor to wake up, process
the RA, attend to other pending tasks, and then go back to sleep
again. Thus, on such devices the cost of receiving one RA will be
approximately 0.014mAh.
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In order to limit the amount of power used to receive Router
Advertisements to, say, 2% of idle power (i.e., to impact idle
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
per hour. Due to background multicast loss and the tendency of
current devices to rate-limit multicast when asleep, many of these
RAs might not reach the device. Thus the minimum lifetimes for RA
configuration parameters such as default router lifetime might
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
negligible, since on this sort of device average power consumption
is typically much higher than idle power consumption.
o Specialized devices in non-general-purpose networks such as sensor
networks might have tighter requirements. In these environments,
even longer RA intervals might be appropriate.
5. Recommendations
5.1. Network-side recommendations
1. Router manufacturers SHOULD allow network administrators to
configure the routers to respond to Router Solicitations with
unicast Router Advertisements if:
* The Router Solicitation's source address is not the
unspecified address, and:
* The solicitation contains a valid Source Link-Layer Address
option.
2. Administrators of networks that serve large numbers (tens or
hundreds) of battery-powered devices SHOULD enable this
behaviour.
3. Networks that serve battery-powered devices SHOULD NOT send
multicast RAs too frequently (see section Section 4) unless the
information in the RA packet has substantially changed. If there
is a desire to ensure that hosts pick up configuration changes
quickly, those networks MAY send frequent Router Advertisements
for a limited period of time (e.g., not more than one minute)
immediately after a configuration change.
No protocol changes are required. Responding to Router Solicitations
with unicast Router Advertisements is already allowed by section
6.2.6 of [RFC4861], and Router Advertisement intervals are already
configurable by the administrator to a wide range of values.
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5.2. Device-side recommendations
1. Maintaining IPv6 connectivity requires that hosts be able to
receive periodic multicast RAs [RFC4861] Therefore, hosts that
process unicast packets sent while they are asleep MUST also
process multicast RAs sent while they are asleep. Battery-
powered hosts MAY rate-limit identical RAs if they are sent too
frequently.
2. Battery-powered devices that do not intend to maintain IPv6
connectivity while asleep SHOULD either disconnect from the
network, abandoning all IPv6 configuration on that network, or
perform 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
Misconfigured or malicious hosts sending rogue Router Advertisements
[RFC6104] can also severely impact power consumption on battery-
powered hosts if they send a significant number of such messages.
Any IPv6 network where there is potential for misconfigured or
malicious hosts should take appropriate countermeasures to mitigate
the problem.
9. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[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,
<http://www.rfc-editor.org/info/rfc4861>.
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[RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for
Detecting Network Attachment in IPv6", RFC 6059, DOI
10.17487/RFC6059, November 2010,
<http://www.rfc-editor.org/info/rfc6059>.
Authors' Addresses
Andrew Yourtchenko
Cisco
7a de Kleetlaan
Diegem, 1831
Belgium
Phone: +32 2 704 5494
Email: ayourtch@cisco.com
Lorenzo Colitti
Google
Roppongi 6-10-1
Minato, Tokyo 106-6126
JP
Email: lorenzo@google.com
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