WiFi router as an IPv6 "switch" between wireless and wired

I have a WiFi router. It currently receives IPv6 multicast packets over a link-local address space in a WiFi network.

What I would like for it to do is to transfer those packets to an Ethernet interface it has (and vice versa) - as if the device connected to this router via Ethernet received these packets over a link-local broadcast itself.

I've tried looking up the keywords "bridging" and "relaying", and gave installing relayd a shot - all to no avail.

What should one do to achieve this goal? I control the WiFi router and the wired device, but the structure of the network traffic itself is unfortunately non-negotiable.

Is this device running OpenWrt?

A switch is a layer 2 device... it simply forwards traffic from one port to another, or if it's an AP, from ethernet <-> wifi when in AP mode.

If the device is in a wifi sta (client) mode configuration, it cannot operate as a transparent bridge unless you use a method like relayd, but this is actually a bit of a routing 'hack' and it applies only to IPv4 (based on the information in the article)... IPv6 does not traverse this bridge.

WDS/ 4addr also works fine with IPv6, if your uplink AP is also running OpenWrt.

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Unfortunately, the underlying protocol for the wireless connection is IBSS/ad-hoc. There's no uplink per se - and I don't think WDS works with that either.

Reading between the lines, are you trying to only bridge this multicast traffic? Or is this intended to be a full bridge?

If the latter, manually adding the wireless adhoc/IBSS interface to the wired side's existing bridge device (or create a new one with both wired and wireless "ports" and move the layer 3 interface if none exists) might be worth a try. I've done that and as far as I can tell broadcast IPv6 traffic traverses the bridge - but, my wireless side is WDS.

(Note, with this I mean adding the wireless port to the br-* defice in its list of ports directly, not as part of a layer 3 "interface")

If the layer 2 bridge doesn't work... Would some macvlan craziness to spoof the IBSS MAC on the wired side work in conjunction with relayd?