Modifying Global Pvst+ Parameters - Dell Force10 Z9000 Configuration Manual

The bridge with the bridge value for bridge priority is elected root. Because all bridges use the default priority (until configured
otherwise), the lowest MAC address is used as a tie-breaker. To increase the likelihood that a bridge is selected as the STP root,
assign bridges a low non-default value for bridge priority.
To assign a bridge priority, use the following command.
• Assign a bridge priority.
PROTOCOL PVST mode
vlan bridge-priority
The range is from 0 to 61440.
The default is 32768.
Example of the show spanning-tree pvst vlan Command
To display the PVST+ forwarding topology, use the show spanning-tree pvst [vlan vlan-id] command from EXEC
Privilege mode.
Dell_E600(conf)#do show spanning-tree pvst vlan 100
VLAN 100
Root Identifier has priority 4096, Address 0001.e80d.b6d6
Root Bridge hello time 2, max age 20, forward delay 15
Bridge Identifier has priority 4096, Address 0001.e80d.b6d6
Configured hello time 2, max age 20, forward delay 15
We are the root of VLAN 100
Current root has priority 4096, Address 0001.e80d.b6d6
Number of topology changes 5, last change occurred 00:34:37 ago on Te 1/32
Port 375 (TenGigabitEthernet 1/22) is designated Forwarding
Port path cost 20000, Port priority 128, Port Identifier 128.375
Designated root has priority 4096, address 0001.e80d.b6:d6
Designated bridge has priority 4096, address 0001.e80d.b6:d6
Designated port id is 128.375 , designated path cost 0
Number of transitions to forwarding state 2
BPDU sent 1159, received 632
The port is not in the Edge port mode
Port 385 (TenGigabitEthernet 1/32) is designated Forwarding
Port path cost 20000, Port priority 128, Port Identifier 128.385
Designated root has priority 4096, address 0001.e80d.b6:d6
Designated bridge has priority 4096, address 0001.e80d.b6:d6
Designated port id is 128.385 , designated path cost 0

Modifying Global PVST+ Parameters

The root bridge sets the values for forward-delay and hello-time, and overwrites the values set on other PVST+ bridges.
• Forward-delay — the amount of time an interface waits in the Listening state and the Learning state before it transitions to the
Forwarding state.
• Hello-time — the time interval in which the bridge sends bridge protocol data units (BPDUs).
• Max-age — the length of time the bridge maintains configuration information before it refreshes that information by
recomputing the PVST+ topology.
To change PVST+ parameters on the root bridge, use the following commands.
• Change the forward-delay parameter.
PROTOCOL PVST mode
vlan forward-delay
The range is from 4 to 30.
Per-VLAN Spanning Tree Plus (PVST+)
571