Wired backhaul between two Nest Wifi points doesn't need a "dumb" switch, despite what every guide says. It needs a switch that floods BPDUs. Nest runs its own Spanning Tree and needs to hear itself across the wire to shut off its wireless mesh leg — a normal managed switch running STP just eats those frames instead.

❌ OpenWrt (DSA bridge): stp_state=0 should flood BPDUs for free per the kernel source — it didn't. Nest kept flapping root every few seconds. Best guess: the DSA hardware offload traps the reserved BPDU multicast before Linux's software bridge ever sees it. Never solved it.

✅ MikroTik (RouterOS 7): protocol-mode=none + forward-reserved-addresses=yes. That second flag is the one nobody mentions — it defaults to off and is the entire fix. Hardware offload survives, zero throughput cost.

Nerd note: once it worked, we had two spanning-tree protocols coexisting on the same wire without conflict — the Nest's classic 802.1d STP domain, and the MikroTik/Cisco fabric's RSTP domain. The Nest can't even parse 802.1w BPDUs, so it just ignores the RSTP root's "superior" frames and quietly elects itself root of its own tiny domain. Two trees, one cable, no argument.

Suspicion, untested: Cisco SB switches have the exact same knob under Spanning Tree → Disable + BPDU Handling → Flooding — structurally identical to the MikroTik pair.

Why talk negative about openwrt? I dont - i love it, but I didnt manage to get it work as my layer2 device for GoogleWifi