I would like to monitor my IPv4 and IPv6 traffic separately using luci-app-statistics, and the easiest way to do that seemed to be putting wan and wan6 on separate VLANs. I could create the new VLAN and assign wan6 to it just fine, but if I left the WAN interface untagged in both definitions the new VLAN wouldn't pass IPv6 traffic. If I tagged them both, then neither VLAN passed traffic. If I untag eth0.2 (the original, assigned only to wan in the config I tried) then it works, but tagged or untagged the new VLAN won't pass IPv6 traffic at all.
At this point I've read the docs on VLANs, and a bunch of forum posts, wiki articles, etc. on similar topics, but I haven't found any solutions. I'm sure it's probably something simple and obvious, but network config is not my area of expertise.
Any help or suggestions appreciated on either having wan and wan6 on separate VLANs, or another way to monitor the traffic separately with luci-app-statistics, or another solution.