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Community Member

Spanning- tree priority with VPC

Hi,

I'm deploying a pair of Nexus 3064 switches in a VPC and they will handle all of the Layer 3 Routing and switching for a small data center.  My question is, should I set their spanning tree priority the same if they will be configured as a VPC?

Example:

Primary - 4096

secondary - 4096

Thank you

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Accepted Solutions
Community Member

Re: Spanning- tree priority with VPC

Hi,

Having the same bridge priority is not a requirement to maintain vPC consistency.

Even if you had the highest bridge priority in the secondary, your vPC primary would forward BPDUs in vPC domain.

quoted from "Cisco NX-OS Virtual PortChannel: Fundamental Design Concepts..."

"vPC by default ensures that only the primary switch forwards BPDUs on vPCs. This modification is strictly limited to

vPC member ports. As a result, the BPDUs that may be received by the secondary vPC peer on a vPC port are

forwarded to the primary vPC peer through the peer link for processing.

Note: Non-vPC ports operate like regular spanning-tree ports. The special behavior of the primary vPC member

applies uniquely to ports that are part of a vPC."

{some articles for refe}

http://www.cisco.com/en/US/prod/collateral/switches/ps9441/ps9670/design_guide_c07-625857.pdf

http://www.cisco.com/en/US/prod/collateral/switches/ps9441/ps9670/C07-572834-00_STDG_NX-OS_vPC_DG.pdf

Having the same (highest) priority would also be no problem because in the non-vPC context (i.e. classic spanning tree topology) there would be a tie-breaker (lowest MAC) to elect the root.

Afterall I suppose it's a choice of design.

2 REPLIES
Community Member

Re: Spanning- tree priority with VPC

Hi,

Having the same bridge priority is not a requirement to maintain vPC consistency.

Even if you had the highest bridge priority in the secondary, your vPC primary would forward BPDUs in vPC domain.

quoted from "Cisco NX-OS Virtual PortChannel: Fundamental Design Concepts..."

"vPC by default ensures that only the primary switch forwards BPDUs on vPCs. This modification is strictly limited to

vPC member ports. As a result, the BPDUs that may be received by the secondary vPC peer on a vPC port are

forwarded to the primary vPC peer through the peer link for processing.

Note: Non-vPC ports operate like regular spanning-tree ports. The special behavior of the primary vPC member

applies uniquely to ports that are part of a vPC."

{some articles for refe}

http://www.cisco.com/en/US/prod/collateral/switches/ps9441/ps9670/design_guide_c07-625857.pdf

http://www.cisco.com/en/US/prod/collateral/switches/ps9441/ps9670/C07-572834-00_STDG_NX-OS_vPC_DG.pdf

Having the same (highest) priority would also be no problem because in the non-vPC context (i.e. classic spanning tree topology) there would be a tie-breaker (lowest MAC) to elect the root.

Afterall I suppose it's a choice of design.

Community Member

Spanning- tree priority with VPC

Thank you for the detailed explanation.

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