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vPC system MAC & STP MAC address

Answered Question
Jan 21st, 2014
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The system mac and root bridge mac addresses are same on both the primary and secondary vPC. How those are elected and related.


Commands:

sh vpc role

sh spanning-tree


Thanks,

Manu

Correct Answer by Steve Fuller about 3 years 6 months ago

Hi Manu,


As Amit says, the MAC addresses are assigned from an internal resource on the switch. On the Nexus 7000 the show sprom backplane command will give you the starting MAC and the number available.


Regards

Correct Answer by Amit Singh about 3 years 6 months ago

VPC Primary switch MAC-address. I think this is assigned by the switch resoruces internally.


Cheers,

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Amit Singh Wed, 01/22/2014 - 00:38
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Hi Manu,


That is the VPC magic :-). That being said,when you have device configured as the VPC-peer, they use a common system MAC or the Primary VPC switch to be forwarded to the downlink devices for the STP. This way we modify the STP behaviour and the VPC domain represent itself as a single root bridge to STP which runs in the background. The downlink devices see the BPDU's coming from a single device as this is all controlled by the VPC Primary switch. VPC Primary switch syncronizes the STP state with peer switch using CFSoE. Once both the peers are synced, all the VPC ports are controlled by the VPC orimary switch.


Hope this helps.


Cheers,

-amit singh

Manu Shankar Wed, 01/22/2014 - 07:42
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Thank you Amit.


I have a vPC between two N7K. I did show spanning-tree and show vpc role on both the device. The vpc-system mac (sh vpc role) and root-id and bridge-id (sh spanning-tree), all the 6 mac addresses are same. vPC local system-mac is different. So my question is, what mac address is electing as the Nexus root id mac address.


I hope i am not confusing you..:-)


Thanks,

Manu

Correct Answer
Amit Singh Wed, 01/22/2014 - 12:29
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VPC Primary switch MAC-address. I think this is assigned by the switch resoruces internally.


Cheers,

Manu Shankar Wed, 01/22/2014 - 18:39
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Hi Amit, appreciate your help. Sorry to disturb you again. In legacy switches show version command will display the switch mac address. What command can use in Nexus?

Correct Answer
Steve Fuller Thu, 01/23/2014 - 23:47
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Hi Manu,


As Amit says, the MAC addresses are assigned from an internal resource on the switch. On the Nexus 7000 the show sprom backplane command will give you the starting MAC and the number available.


Regards

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