Reference Guide

644 | Per-VLAN Spanning Tree Plus (PVST+)
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The values for global PVST+ parameters are given in the output of the command show spanning-tree pvst,
as shown in Figure 32-4.
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 32-2 lists the default values for port cost by interface.
To change the port cost or priority of an interface:
Change the max-age parameter.
Range: 6 to 40
Default: 20 seconds
vlan max-age
PROTOCOL PVST
Table 32-2. 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
Note: The FTOS implementation of PVST+ uses IEEE 802.1s costs as the default costs. Other
implementations use IEEE 802.1d costs as the default costs if you are using Dell Force10systems in a
multi-vendor network, verify that the costs are values you intended.
Task Command Syntax Command Mode
Change the port cost of an interface.
Range: 0 to 200000
Default: see Table 32-2.
spanning-tree pvst vlan cost
INTERFACE
Task Command Syntax Command Mode