Dell PowerEdge FN I/O Module Configuration Guide 9.10(0.0)

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. For information on PVST+, refer to Per-VLAN Spanning Tree Plus (PVST+) .

Run PVST+ on both VLT peer switches. PVST+ instance will be created for every VLAN configured in the system. PVST+ instances running in the Primary Peer will 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. PVST+ instance in Primary peer will send the role/state of VLT-LAGs for all VLANs to the Secondary peer. Secondary peer will use this information to program the hardware. PVST+ instance running in Secondary peer will not control the VLT-LAGs.

Dell 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 (refer to Verifying a VLT Configuration ).

Dell#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 0/100   128.230  128  2000    FWD         0       0     90b1.1cf4.9b79  128.230 
                                 Te 0/103   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 0/100   Desg   128.230  128  2000    FWD         0       P2P       Yes 
                                 Te 0/103   Desg   128.233  128  2000    FWD         0       P2P       No
                                 Dell#