IPv6 Operations A. Yourtchenko
Internet-Draft cisco
Intended status: Best Current Practice L. Colitti
Expires: January 24, 2016 Google
July 23, 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 messages. 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 (e.g., once every few seconds). This may be due to a desire to ensure that hosts always have access to up-to-date router information.

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. Recommendations

  1. Router manufacturers SHOULD allow network administrators to configure the routers to respond to with unicast Router Advertisements to Router Solicitations if:
  2. 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 (e.g., more than one every 5-10 minutes for current battery-powered devices) 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. Acknowledgements

The authors wish to thank Steven Barth, Erik Kline, Erik Nordmark, Alexandru Petrescu, and Mark Smith for feedback and helpful suggestions.

6. IANA Considerations


7. Security Considerations


8. 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.

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