STP blocking Port Channel

[AsifParkar20245]

I am trying to connect Nexus 5k to nexus 9k over a fiber link. This is a single Port channel VPC with 1 interface in the Po. The CDP is up, but one of Port channel remains in BLK state and we are getting below logs :

log: STP-2-BRIDGE_ASSURANCE_BLOCK: Bridge Assurance blocking port ; Po 20 

Below is the config on the Nexus 5ks and similar config is at the other end Nexus switch.

interface port-channel20

switchport mode trunk
switchport trunk allowed vlan 20
speed 1000
vpc 20

interface Ethernet1/19
switchport mode trunk
switchport trunk allowed vlan 20
speed 1000
channel-group 20

We tried to add "spanning tree port type normal " to the other end Nexus, but it just blocked the 5ks port channel in STP. what could be the issue with STP?

[Sergiu.Daniluk]

Hi @AsifParkar20245 

If I understand correctly you get the message on N5K right?

If the interface is in BA BLK state, it means you have bridge assurance configured on the port-channel/interface and it does not receive STP BPDUs on it. So you either configure the interface with "spanning tree port type normal" on both vPC peers (on both N5K), or you configure "spanning tree port type network" on both N9K.

Take care,

Sergiu

[AsifParkar20245]

yes on my both switches Spanning tree Bridge assurance is globally configured and we tried to configure "spanning tree port type normal " and "spanning tree port type network" on both ends but still one of the interface ends up in spanning tree blocked state

[Sergiu.Daniluk]

Can you share the following from all 4 switches? 

show run int po 20

show spanning-tree interface po 20

Cheers,

Sergiu