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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. 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
---------- -------- ---- ------ ----------- ------- --------------------
--------
988
Virtual Link Trunking (VLT)