What is the most effective and least cpu intensive way to either block all ip4 traffic passing over a bridged group of interfaces? So only ipv6 traffic can pass I’m trying to overcome prefix delegation not working on my isp’s router I’m trying to setup a second device to act as a ipv6 gateway.

Use bridge filter (/interface bridge filter) to block frames with mac-protocol=ip . You may have to disable HW offload (bridge filtering is CPU-bound) or configure similar directly on switch chip is your device has capable switch chip.

Or for block all except ipv6: mac-protocol = ! ipv6

Thanks I will give this go….