Sending Solicited RAs Unicast
draft-yc-v6ops-solicited-ra-unicast-00

Abstract

On links with a large number of mobile devices, sending Solicited Router Advertisement as multicast packets can severely impact host power consumption. This document recommends that on such network, RAs be sent unicast.

Status of This Memo

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Copyright Notice

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Table of Contents

• 1. Introduction
• 2. Consequences
• 3. Recommendations
• 4. Acknowledgements
• 5. IANA Considerations
• 6. Security Considerations
• 7. Normative References
• Authors' Addresses

1. Introduction

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].

On links with a large number of mobile devices, sending solicited Router Advertisements as multicast packets 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. Consequences

Observed host reactions to this include:

• Some hosts simply experience bad battery life on these networks and otherwise operate normally. This is frustrating for users of these networks.
• Some hosts react by dropping all Router Advertisement packets 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.
• 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.

3. Recommendations

Router manufacturers SHOULD allow network administrators to configure the routers to respond to Router Solicitations with unicast Router Advertisements.

Networks that serve large numbers (tens or hundreds) of mobile devices SHOULD enable this behaviour.

No protocol changes are required, since responding to Router Solicitations with unicast Router Advertisements is already allowed by section 6.2.4 of [RFC4861].

4. Acknowledgements

5. IANA Considerations

None.

6. Security Considerations

Not discussed in -00.

7. Normative References

Authors' Addresses