Upload this file to /etc/hotplug.d/iface/

80-imlk-ebtables-ipv6

#!/bin/sh

# imlk: setup ipv6 bridge while ipv4 is nat mode. see https://jethro.fun/index.php/archives/162/

logger -t imlk-ebtables-ipv6 "hotplugin event: $INTERFACE -> $ACTION"

if [[ "$INTERFACE" != "wan" ]]; then
        exit
fi

case "$ACTION" in
ifup)
logger -t imlk-ebtables-ipv6 "setup ipv6 passthrough ..."

# force non-ipv6 packet to be routed
ebtables -t broute -A BROUTING -p ! ipv6 -j DROP -i eth0.2
# drop some bad devices in UCAS
ebtables -t filter -A FORWARD --src 5c:02:14:73:1c:b6 -j DROP
ebtables -t filter -A FORWARD --src 8c:de:f9:ec:92:be -j DROP
ebtables -t filter -A FORWARD --src 54:ee:75:f2:85:12 -j DROP
brctl addif br-lan eth0.2

logger -t imlk-ebtables-ipv6 "setup ipv6 passthrough done!" 
;;
ifdown)
logger -t imlk-ebtables-ipv6 "revert ipv6 passthrough ..." 

brctl delif br-lan eth0.2
ebtables -t broute -D BROUTING -p ! ipv6 -j DROP -i eth0.2

logger -t imlk-ebtables-ipv6 "revert ipv6 passthrough done!" 
;;
esac