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Dell Configuration Guide for the S4048–ON System 9.14.2.6

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PVST+ Configuration

PVST+ is supported in a VLT domain.

Before you configure VLT on peer switches, configure PVST+ in the network. PVST+ is required for initial loop prevention during the VLT startup phase. You may also use PVST+ for loop prevention in the network outside of the VLT port channel.

Run PVST+ on both VLT peer switches. A PVST+ instance is created for every VLAN configured in the system. PVST+ instances running in the Primary Peer control the VLT-LAGs on both Primary and Secondary peers. Only the Primary VLT switch determines the PVST+ roles and states on VLT ports and ensures that the VLT interconnect link is never blocked. The PVST+ instance in Primary peer sends the role/state of VLT-LAGs for all VLANs to the Secondary peer. The Secondary peer uses this information to program the hardware. The PVST+ instance running in Secondary peer does not control the VLT-LAGs.

Dell EMC Networking recommends configuring the primary VLT peer as the primary root device for all the configured PVST+ Instances and configuring the secondary VLT peer as the secondary root device for all the configured PVST+ Instances.

Sample PVST+ Configuration

The following examples show the PVST+ configuration that you must perform on each peer switch to prevent forwarding loops.

Configure PVST+ on VLT Peers to Prevent Forwarding Loops (VLT Peer 1)
Dell_VLTpeer1(conf)#protocol spanning-tree pvst
Dell_VLTpeer1(conf-pvst)#no disable 
Dell_VLTpeer1(conf-pvst)#vlan 1000 bridge-priority 0
Configure PVST+ on VLT Peers to Prevent Forwarding Loops (VLT Peer 2)
Dell_VLTpeer2(conf)#protocol spanning-tree pvst 
Dell_VLTpeer2(conf-pvst)#no disable 
Dell_VLTpeer2(conf-pvst)#vlan 1000 bridge-priority 4096

Configure both ends of the VLT interconnect trunk with identical PVST+ configurations. When you enable VLT, the show spanning-tree pvst brief command output displays VLT information.

DellEMC#show spanning-tree pvst vlan 1000 brief 
VLAN 1000
Executing IEEE compatible Spanning Tree Protocol
Root ID    Priority 0, Address 90b1.1cf4.9b79
Root Bridge hello time 2, max age 20, forward delay 15
Bridge ID    Priority 0, Address 90b1.1cf4.9b79
We are the root of Vlan 1000
Configured hello time 2, max age 20, forward delay 15

Interface                                                Designated                  
 Name      PortID   Prio Cost    Sts          Cost        Bridge ID        PortID
---------- -------- ---- ------  ----------- ------- -------------------- --------
Po 1       128.2    128  188     FWD(vltI)   0       0     90b1.1cf4.9b79  128.2   
Po 2       128.3    128  2000    FWD(vlt)    0       0     90b1.1cf4.9b79  128.3   
Te 1/10    128.230  128  2000    FWD         0       0     90b1.1cf4.9b79  128.230 
Te 1/13    128.233  128  2000    FWD         0       0     90b1.1cf4.9b79  128.233 

Interface
 Name      Role   PortID   Prio Cost    Sts         Cost    Link-type Edge
---------- ------ -------- ---- ------- ----------- ------- --------- ----
Po 1       Desg   128.2    128  188     FWD         0       (vltI)P2P No  
Po 2       Desg   128.3    128  2000    FWD         0      (vlt) P2P No  
Te 1/10    Desg   128.230  128  2000    FWD         0       P2P       Yes 
Te 1/13    Desg   128.233  128  2000    FWD         0       P2P       No
DellEMC#

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