Master/Backup Routing Setup and issues with Windows Clients

[bfr]

Hi,

we are running 2 pfSense 2.3.2 boxes as master/slave. The network connected to both boxes is using a /64 prefix, which is announced via radvd on the master. The whole prefix gets routed via an IPv6-address on a WAN-CARP Interface.  To create redundancy I also tried to announce the prefix (with router priority low) via the backup system. WIndows clients connected to the network got confused because they got both default gateways with the same metrics, which seems to be related to https://redmine.pfsense.org/issues/6237

According to the rc.carpmaster/slave code, radvd would be reconfigured when the master/slave status changes:

if (isset($config['dhcpdv6']) && is_array($config['dhcpdv6'])) {
	$rafound = false;
	foreach ($config['dhcpdv6'] as $dhcpv6if => $dhcpv6ifconf) {
		foreach ($vips as $vip) {
			if ($dhcpv6ifconf['rainterface'] == "_vip{$vip['uniqid']}") {
				log_error("Starting radvd instance on {$friendly_descr} because of transition to CARP master.");
				$rafound = true;
			}
		}
	}
	if ($rafound) {
		services_radvd_configure();
	}
}

If I understand this correctly, the reconfiguration is only done when radvd is running on a carp interface, but radvd can be only enabled on usual interfaces?

What would be the best practice for such a setup without confusing the windows clients?