Nexus 9000 peer-link is blocked

[Dmitryvolkov4646]

Hi team,

I have two Nexus 9k (vPC) with peer-switch configuration and MST (all vlans are in MST0) with the same priority.

One of the vPC peer was down and immediately after that I can see in log that port-channel4 (peer-link) was changed to blocking from secondary switch because of Superior BPDU .

It is not clear for me how Superior BPDU can block peer-link in this configuration? From my understanding peer-link MUST be in forwarding state all the time.

Unfortunately MST with vPC is not fully described in documentation. Could you please help me with the idea why Superior BPDU is on peer-link with peer-switch configuration.

[Sergiu.Daniluk]

Hi @Dmitryvolkov4646 

I found one of my old posts about MST & VPC:

https://community.cisco.com/t5/data-center-switches/nexus-9300-nx-os-vpc-and-mst-considerations/td-p/4114647

"while configuring peer-switch w/ MST, do not map any vlan to MSTI 0. Always create a new instance and map the vlans to that instance."

I must admit I do not know why I made this recommendation, I will try and check for the source reference.

Cheers,

Sergiu