RSTP DISPUTE BLOCKED port _BPUDs behaviour

[NDP]

have one query

Spanning-tree root switch --> Nexus Layer 2 Aggregation switches( VPC)-->ACi Fabric---> 4 Access switches 

As far as BPDUs are concerned, ACI is a hub. if We connect switches which are in RSTP ( as above) and there is DISPUTE detected on Nexus Layer 2 Aggregation switches ( VPC) and blocked the port ( root guard also enabled on VPC connected to ACI fabric)

I understood that the Dispute message is because of the inferior BPDUs and root guard enabled on nexus VPC. in this case, does the blocked port ( due to dispute) send BPDUs to other switches through ACI fabric?

All the access switches interfaces are in Point to point ( not in shared :-( )

Thank you in advance

[Georg Pauwen · Accepted solution]

Hello,

in theory, root guard would put the port where the superior BPDU is received in root-inconsistent state, which is effectively the listening state. Which means, no traffic is forwarded. As to BPDUs sent or received, enable debugging:

debug spanning-tree bpdu 

or 

show spanning-tree vlan x

and check if the BPDU sent/receive counters increase.

[NDP]

Hi Georg,

I didn't see BPDUs sent on interface when the port was blocked (DISPUTE reason) for specific VLAN on Nexus 7K switches.

I believe that DISPUTE is not to accept another bridge with inferior BPDUs as root. (happens when Unidirection link failure happens)

would like to understand the behaviour of the port r, when the role is blocked due to Dispute. does it still send BPDUs on the port for blocked VLAN

[rafafilho11]

Any L2 interface connected tô ACI leaf must bê configurei as spanning-tree link type shared.

https://www.cisco.com/c/pt_br/support/docs/cloud-systems-management/application-policy-infrastructure-controller-apic/211236-ACI-operation-with-L2-switches-and-Spann.html