N7K Peer-switch Konfiguration

Question

Hi I have a question regarding peer-switch konfiguration on a vPC/vPC+ pair of N7K with vPC and non vPC attached switches
If I understood correctly with following configuration
for vPC attached switches (assuming the have default STP-prio) the vPC-bundle acts as one Switch with the priority of 4096
for STP non-VPC attached switches for VLAN1-1960 the N7K-A is the root-bridge and for VLAN 1961-3920 the N7K-B is the root-bridge,
N7K-A
vpc domain 20
  peer-switch
  role priority 1
spanning-tree pseudo-information
vlan 1-3920 root priority 4096                 
  vlan 1-1960 designated priority 4096
  vlan 1961-3920 designated priority 8192
N7K-B
vpc domain 20
peer-switch
role priority 2
spanning-tree pseudo-information
  vlan 1-3920 root priority 4096
  vlan 1-1960 designated priority 8192
  vlan 1961-3920 designated priority 4096
Is that coorect so far ?
If yes then I have one outstandig question.
Do we need the global configuration for spanning-tree priority in this case?
spanning-tree vlan 1-3920 priority 4096
as we configure it in a pure vPC environment
N7K-A
spanning-tree vlan 1-3920 priority 4096
vpc domain 20
peer-switch
role priority 1
N7K-B
spanning-tree vlan 1-3920 priority 4096
vpc domain 20
peer-switch
role priority 2
Thanks
Hubert

Answer 1

Here is a description of the use of the Spanning-tree Pseudo-information and the Peer switch command on the Nexus 7000. Maybe this will help clarify some misunderstanding:
SETUP:
7K1 and 7K2 are vPC peers and have a higher priority      than 7K3. So 7K1 and 7K2s ports to 7K3 will all be DESIGNATED.
7K3 is connected to both 7K1 and 7K2 using individual      STP links.
7K4 is connected to both 7K1 and 7K2 in a vPC.
Common Points for all Scenarios:
If vPC fails for whatever reason; all links will revert      to regular spanning-tree.
The root priority on 7K1 and 7K2 will be the vPC System-MAC (same on both) and the Designated priority will use the respective non-vPC System-MACs of 7k1 and 7K2
Even if the STP Priority is configured globally and lower, the Pseudo Root Priority and Designated Priorities are still used for STP calculations.
The STP Pseudo-information HACK:
Allows you to set a different root priority and different designated priority. To satisfy the requirement for the Peer switch command and still be able to perform VLAN load balancing for non-vPC dual connected links.
Root Priority: Used in Root Bridge Election
Designated Priority: Used in Designated Bridge Election
SCENARIO 1: Same STP Priority configured Globally with the Peer switch Enabled (Individual STP links)
The Root priority and Designated priority on 7K1 and 7K2 will be the same as the globally configured or default STP priority
One of the links to 7K1 and 7K2 becomes the "Root Port" and the other becomes "ALTN BLK"
Since they have the same Root Priority and the same vPC system MAC, the lower port will be selected as the root port.
SCENARIO 2: BOTH STP Pseudo-information Root and Designated Priorities Configured with Peer Switch Enabled (Individual STP links)
The Root priority may be different from the Designated Priority based on the STP Pseudo-information configuration.
VLAN traffic from 7K3 is load balanced between 7K1 and 7K2 based on the configured Pseudo-Designated Priority. So the Root port for a VLAN from 7K3 will be to the device with a lower Pseudo-Designated priority.
SCENARIO 3: ONLY STP Pseudo-information Root Priority Configured with Peer Switch Enabled (Individual STP links)
The Root priority and Designated Priority are the same as the Pseudo Root Priority.
No VLAN load balancing occurs
The Root port is the link to the vPC primary switch. The Link to the vPC Secondary is “ALTN BLK”.
SCENARIO 4: ONLY STP Pseudo-information Designated Priority Configured with Peer Switch Enabled (Individual STP links)
The Root priority will be the Globally configured or default STP Priority
The Designated priority will still be the Pseudo-Designated priority
VLAN load balancing will still occur.
SCENARIO 5: Same STP Priority configured Globally with the Peer switch Enabled (vPC links on 7K4)
The Root priority and Designated priority on 7K1 and 7K2 will be the same as the globally configured or default STP priority.
If the vPC Peer-link fails, the interface going to the secondary vPC device (7K2) will be shut DOWN.
SCENARIO 6: BOTH STP Pseudo-information Root and Designated Priorities Configured with Peer Switch Enabled (vPC links on 7K4)
The Root priority and Designated Priority are the same as the configured Pseudo-Root Priority.
If the vPC Peer-link fails, the interface going to the secondary vPC device (7K2) will be shut DOWN.
SCENARIO 7: ONLY STP Pseudo-information Root Priority Configured with Peer Switch Enabled (vPC links on 7K4)
The Root priority and Designated Priority are the same as the configured Pseudo-Root Priority.
If the vPC Peer-link fails, the interface going to the secondary vPC device (7K2) will be shut DOWN.
SCENARIO 8: ONLY STP Pseudo-information Designated Priority Configured with Peer Switch Enabled (vPC links on 7K4)
The Root priority and Designated priority on 7K1 and 7K2 will be the same as the globally configured or default STP priority.
If the vPC Peer-link fails, the interface going to the secondary vPC device (7K2) will be shut DOWN