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Versions: (draft-yc-v6ops-solicited-ra-unicast) 00 01 02 03 RFC 7772

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.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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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.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.




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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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