Reference Guide

Per-VLAN Spanning Tree Plus | 789
To change PVST+ parameters, use the following commands on the root bridge:
The values for global PVST+ parameters are given in the output of the command
show spanning-tree pvst,
as shown in the example in Influence PVST+ Root Selection.
Modify Interface PVST+ Parameters
You can adjust two interface parameters to increase or decrease the probability that a port becomes a
forwarding port:
• Port cost is a value that is based on the interface type. The greater the port cost, the less likely the port
will be selected to be a forwarding port.
• Port priority influences the likelihood that a port will be selected to be a forwarding port in case that
several ports have the same port cost.
Table 43-2, "PVST+ Default Port Cost Values," in Per-VLAN Spanning Tree Plus lists the default values
for port cost by interface.
Task Command Syntax Command Mode
Change the forward-delay parameter.
• Range: 4 to 30
• Default: 15 seconds
vlan forward-delay
PROTOCOL PVST
Change the hello-time parameter.
Note: With large configurations (especially those with more ports) Dell
Force10 recommends that you increase the hello-time.
Range: 1 to 10
Default: 2 seconds
vlan hello-time
PROTOCOL PVST
Change the max-age parameter.
Range: 6 to 40
Default: 20 seconds
vlan max-age
PROTOCOL PVST
Table 43-2. PVST+ Default Port Cost Values
Port Cost Default Value
100-Mb/s Ethernet interfaces 200000
1-Gigabit Ethernet interfaces 20000
10-Gigabit Ethernet interfaces 2000
Port Channel with 100 Mb/s Ethernet interfaces 180000
Port Channel with 1-Gigabit Ethernet interfaces 18000
Port Channel with 10-Gigabit Ethernet interfaces 1800