Concept Guide

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.
The default is 15 seconds.
● Change the hello-time parameter.
PROTOCOL PVST mode
vlan hello-time
NOTE:
With large configurations (especially those configurations with more ports), Dell EMC Networking recommends
increasing the hello-time.
The range is from 1 to 10.
The default is 2 seconds.
● Change the max-age parameter.
PROTOCOL PVST mode
vlan max-age
The range is from 6 to 40.
The default is 20 seconds.
The values for global PVST+ parameters are given in the output of the show spanning-tree pvst command.
Modifying Interface PVST+ Parameters
You can adjust two interface parameters (port cost and port priority) to increase or decrease the probability that a port
becomes a forwarding port.
● Port cost — a value that is based on the interface type. The greater the port cost, the less likely the port is selected to be
a forwarding port.
Per-VLAN Spanning Tree Plus (PVST+)
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