Install Guide

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.
● Port priority — influences the likelihood that a port is selected to be a forwarding port in case that several ports have the
same port cost.
The following tables lists the default values for port cost by interface.
Table 72. Default Values for Port Cost
Port Cost Default Value
100-Mb/s Ethernet interfaces 200000
1-Gigabit Ethernet interfaces 20000
10-Gigabit Ethernet interfaces 2000
25-Gigabit Ethernet interfaces 1700
40-Gigabit Ethernet interfaces 1400
50-Gigabit Ethernet interfaces 1200
100-Gigabit Ethernet interfaces 200
Per-VLAN Spanning Tree Plus (PVST+) 597