Users Guide

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. 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 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
Virtual Link Trunking (VLT) 1146