It has been a while, but I have seen some switches that don't "speak" STP but still forward the BPDU messages (so other switches receive them and still detect l

It has been a while, but I have seen some switches that don't "speak" STP but still forward the BPDU messages (so other switches receive them and still detect loops through the "non-STP switch") and other switches that drop the BPDUs (so other switches/bridges cannot see them, possibly leading to a Layer 2 forwarding loop through the "non-STP switch").