When spanning tree function is disabled and switch receives a BPDU message, how switch handles this BPDU message?

[kawasakifyu705]

Hi everyone, my colleague and I is arguing a situation, can somebody help to provide some information or evidence (IEEE standard) to me for our arguing point.

The scenario is pretty simple as bellow:

SW_A --- SW_B --- SW_C

SW_A & SW_C  spanning-tree-protocol function are enabled.

SW_A priority=4096

SW_C priority=32768

SW_B spanning-tree-protocol function is disabled by manual.

When BPDU is sent from SW_A & SW_C and arrived at SW_B.

Will SW_B forward those BPDU message? or Will SW_B drop those BPDU message, and then a potential loop might be occurred?

My colleague said: IEEE 802.1D has defined the situation to DROP the BPDU if switch does not enable spanning-tree function. Actually, it looks same behavior within Cisco/HP/Juniper switch. However, I have also found some brands (some industrial devices) with opposite behavior, they FORWARD the BPDU !!!

So, which behavior is correct? Can somebody provide the IEEE 802.1D standard for reference?

[Philip D'Ath]

Lets assume we are not talking about a Cisco switch in the middle, since all Cisco switches can do spanning tree.

I have seen dumb third party switches do both, drop BPDUs and forward them on.

Not a situation you want to be involved in.

[kawasakifyu705]

Hi Philip

Thank you for your response. Are those dumb third switches can not be managed? Because we were arguing for switch's STP function disable/enable.

[Philip D'Ath]

Sometimes they can, sometimes they can't be.

If a device is not processing spanning tree packets, then I believe it should flood the spanning tree packet out every port.