Administrator Guide

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 1/10/1 128.230 128 2000 FWD 0 0 90b1.1cf4.9b79 128.230
Te 1/13/1 128.233 128 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 1/10/1 Desg 128.230 128 2000 FWD 0 P2P Yes
Te 1/10/3 Desg 128.233 128 2000 FWD 0 P2P No
DellEMC#
Peer Routing Configuration Example
This section provides a detailed explanation of how to configure peer routing in a VLT domain.
In the following example, devices are configured as follows:
• Access switch A1 is connected to two VLT peers (Dell-1 and Dell-2).
• The two VLT peers are connected to an upstream switch R1.
• OSPF is configured in Dell-1, Dell-2, and R1 switches.
• Dell-1 is configured as the root bridge.
• Dell-1 is configured as the VLT primary.
916
Virtual Link Trunking (VLT)