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


Frequent Router Advertisement messages can severely impact host power consumption. This document recommends operational practices to avoid such impact.

Status of This Memo

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Table of Contents

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. 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:

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.

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:
  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.

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


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.
[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.
[RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for Detecting Network Attachment in IPv6", RFC 6059, DOI 10.17487/RFC6059, November 2010.

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