vPC & STP BPDUs

Unanswered Question
Jul 28th, 2013
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Hello all,

According to Design and Configuration Guide : Best Practices for Virtual Port Channels (vPC) on Cisco Nexus 7000 Series Switches

Assumptions: peer-swtich is not enabled here.


In vPC deployments, STP is actually running on both peer devices. And for vPC ports, they are controlled only by the STP instance on primary switch (which means only primary switch generates and sends out BPDUs for vPC ports), while STP instance on secondary switch does not dictate vPC member port state. below are my queries:

Q1: In BPDUs sent by primary switch, vPC System-MAC will be used in Bridge ID or vPC Local System-MAC?

Q2: If BPDUs go this path  primary swtich----peer link----secondary switch-----vPC member port----downstream devices, what is the value of Path Cost in BPDU receiced on downstream devices,  Path cost of peer link only or Path cost of peer link + path cost of vPC member port ?

Q3: Both vPC member ports on both peer devices always share the same STP port state (FWD state in a steady network). How could this be achieved from STP perspective?

Q4: Why Cisco Strongly recommends not to enable Loopguard and Bridge Assurance on vPC?

Q5: Why Cisco stronlgy recommends to enable Bridge Assurance on vPC peer-link?


Thanks in advance.

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