Hi all, we're users of Birds RAdv implementation in a mesh networking project with many opportunistic WiFi users on mobile devices. We and our users would likely profit from a reduced rate of router advertisments that we see as a result from high client turnover. RFC7772¹ describes in 5.1: 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 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. There is already an implementation for this behaviour in radvd² with the peculiarity that they ignore missing SLLA, because little to no clients actually sent them back in 2017. Note that the RFC does not make SLLA a MUST. They justify unicast responses in absence of SLLA as follows: However, testing shows that many clients do not set the SLLA option: https://github.com/reubenhwk/radvd/issues/63#issuecomment-287172252 As of 2017/03/16: - macOS 10.12.3 sierra - sends SLLA 2 times out of 4 - iOS 10.2.1 (iPhone 5s) - no SLLA - Android 7.0 (sony xperia phone) - sends SLLA - Android 5.1 (nexus 7 tablet) - sends SLLA - Ubuntu 16.04.2 LTS w/ Network Manager, running 4.9 kernel (dell laptop) - no SLLA - Windows 10 (dell laptop) - no SLLA We decide to ignore the SLLA option for now, and only require the unspecified address check. Clients that did not set the SLLA option will trigger a neighbour solicit to the solicited-node address trying to resolve the link-local address to, this would still be less traffic than the all-nodes multicast. I'd be very happy if you would consider implementing this BCP and would especially appreciate it if there were a knob to make Bird reply with unicast radv replies to router solications and only use multicast advertisments in larger intervals. Thanks for your consideration! Martin Weinelt [1] https://tools.ietf.org/html/rfc7772 [2] https://github.com/reubenhwk/radvd/commit/30328bdbfc1f08ea100de9a6011f981cc4...