Reference Guide

788 | Per-VLAN Spanning Tree Plus
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The bridge with the bridge value for bridge priority is elected root. Since all bridges use the default priority
(until configured otherwise), lowest MAC address is used as a tie-breaker. Assign bridges a low
non-default value for bridge priority to increase the likelihood that it will be selected as the STP root.
Display the PVST+ forwarding topology by entering the command
show spanning-tree pvst [vlan vlan-id]
from EXEC Privilege mode, as shown in the following example.
FTOS_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 Gi 1/32
Port 375 (GigabitEthernet 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 (GigabitEthernet 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
Modify 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 is the amount of time an interface waits in the Listening State and the Learning State
before it transitions to the Forwarding State.
• Hello-time is the time interval in which the bridge sends Bridge Protocol Data Units (BPDUs).
• Max-age is the length of time the bridge maintains configuration information before it refreshes that
information by recomputing the PVST+ topology.
Task Command Syntax Command Mode
Assign a bridge priority.
Range: 0 to 61440
Default: 32768
vlan bridge-priority
PROTOCOL PVST