Re: [PATCH net-next 27/30] net: dsa: mt7530: introduce BPDU trapping for MT7530 switch

Vladimir Oltean
2023-06-04T09:23:49Z

On Sun, Jun 04, 2023 at 11:51:33AM +0300, Arınç ÜNAL wrote:
> > If the switch doesn't currently trap BPDUs, isn't STP broken?
>
> No, the BPDU_PORT_FW bits are 0 after reset. The MT7620 programming guide
> states that frames with 01:80:C2:00:00:00 MAC DA (which is how the BPDU
> distinction is being made) will follow the system default which means the
> BPDUs will be treated as normal multicast frames.
>
> Only if all 3 bits are set will the BPDUs be dropped.

Right, if you don't trap BPDUs just to the CPU but flood them, I believe
the STP protocol won't behave properly with switching loops. Worth testing.