RFC 7772

Reducing Energy Consumption of Router Advertisements

📅 published February 2016, from ietf

Reducing Energy Consumption of Router Advertisements 🦋

Okay bestie, let's get into RFC 7772! 💖 It's a Best Current Practice (BCP 202) from February 2016, written by A. Yourtchenko of Cisco and L. Colitti of Google. It is ISSN 2070-1721, and it doesn't obsolete or update anything, so it's totally standalone 🫶 Its whole vibe is about keeping battery-powered devices from getting drained by too many Router Advertisements. 🔋✨

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 memo documents an Internet Best Current Practice. 🌸

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on BCPs is available in Section 2 of RFC 5741. 👑

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 (c) 2016 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 Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. 📜

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 . . . . . . . . .   3
3.  Consequences  . . . . . . . . . . . . . . . . . . . . . . . .   3
4.  Router Advertisement Frequency  . . . . . . . . . . . . . . .   3
5.  Recommendations . . . . . . . . . . . . . . . . . . . . . . .   4
  5.1.  Network-Side Recommendations  . . . . . . . . . . . . . .   4
  5.2.  Device-Side Recommendations . . . . . . . . . . . . . . .   5
6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
  7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
  7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   6
Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1. Introduction 🌷

Okay so, routing info gets sent to IPv6 hosts through Router Advertisement (RA) messages [RFC4861]. 🦋 If these get sent too frequently, they can seriously drain power 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 multicast Router Advertisements can seriously impact host power consumption. 💀 That's because every time a device joins the network, every other device on the network gets a multicast Router Advertisement. 🙈 In the worst case, if devices keep joining and leaving, and the network is big 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 really often (e.g., once every few seconds). 🥹 This may be because they want to minimize the customer impact of network renumbering events, which in some large residential networks happen pretty frequently. 🏠 With hosts that ignore RAs, or even all IPv6 packets, when they're in sleep mode, these networks may feel like they need to send RAs often so devices don't end up with non-functional IPv6 configurations for long stretches. 😵‍💫 Unfortunately, this is seriously bad for battery life. 🔋💔

3. Consequences 💅

Observed effects of frequently sending Router Advertisement messages to battery-powered devices include:

  • Some hosts just have bad battery life on these networks and otherwise work fine. 😤 That's really frustrating for the users of these networks.
  • Some hosts respond by dropping all Router Advertisement messages when they're in power-saving mode on any network, e.g., <https://code.google.com/p/android/issues/detail?id=32662>. 🙃 This makes devices lose connectivity in power-saving mode, which can mess up background network communications, because the device can no longer send packets or acknowledge received traffic. 📵
  • Some hosts respond by dropping all IPv6 packets when in power-saving mode, <http://www.gossamer-threads.com/lists/nsp/ipv6/54641>. 💀 This disrupts network communications.

It gets worse 🙃: when devices drop Router Advertisements in power-saving mode, some network admins try to work around it by sending RAs even more often. 🫠 That makes devices get even more aggressive about filtering. 🚫

4. Router Advertisement Frequency 🎀

The right frequency for periodic RAs depends on how constrained the network devices are. 🧚

  • Laptop-class devices will likely see no noticeable battery-life impact, even if RAs are sent every few seconds. 💻✨
  • Tablets, phones, and watches feel it more noticeably. ⌚📱 When this was written, current-generation devices might draw on the order of 5 mA when the main processor is asleep. 😴 When they receive a packet, they might draw on the order of 200 mA for 250 ms, since the packet wakes the main processor, which processes the RA, handles other pending tasks, and then goes back to sleep. ⚡ So on these devices, the cost of receiving one RA is about 0.014 mAh. 🧮

To keep the power used to receive Router Advertisements to, say, 2% of idle power (i.e., so idle battery life drops by no more than 2%), the average power budget for receiving RAs must be no more than 0.1 mA, or about 7 RAs per hour. 🍓 Because of background multicast loss, and because current devices tend to rate-limit multicast while asleep, many of these RAs might never reach the device. 📡 So the minimum lifetimes for RA configuration parameters, like the default router lifetime, might reasonably be 5-10 times the RA period, or roughly 45-90 minutes. ⏳

An 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. 👑

  • 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 behavior. 💖
  3. Networks that serve battery-powered devices SHOULD NOT send multicast RAs too frequently (see Section 4) unless the information in the RA packet has substantially changed. ✨ If there's a desire to make sure 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're asleep MUST also process multicast RAs sent while they're asleep. 🛌 Battery-powered hosts MAY rate-limit identical RAs if they're sent too frequently. 🚦
  2. Battery-powered devices that don't intend to maintain IPv6 connectivity while asleep SHOULD either disconnect from the network, abandoning all IPv6 configuration on that network, or perform Detecting Network Attachment in IPv6 (DNAv6) procedures [RFC6059] when waking up. ☀️

6. Security Considerations 🔐

Misconfigured or malicious hosts sending rogue Router Advertisements [RFC6104] can also seriously impact power consumption on battery-powered hosts if they send a significant number of such messages. 🚨 Any IPv6 network where there's potential for misconfigured or malicious hosts should take appropriate countermeasures to mitigate the problem. 🛡️

7. References 📚

7.1. 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>.

[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>.

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 💌

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
Japan

Email: lorenzo@google.com
📦 where this page comes from