Concept Guide

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 — inuences 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 67. 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
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 Dell Networking OS implementation of PVST+ uses IEEE 802.1s costs as the default costs. Other implementations
use IEEE 802.1w costs as the default costs. If you are using Dell Networking systems in a multi-vendor network, verify that the
costs are values you intended.
To change the port cost or port priority of an interface, use the following commands.
• Change the port cost of an interface.
INTERFACE mode
spanning-tree pvst vlan cost.
The range is from 0 to 200000.
Refer to the table for the default values.
• Change the port priority of an interface.
INTERFACE mode
spanning-tree pvst vlan priority.
The range is from 0 to 240, in increments of 16.
The default is 128.
The values for interface PVST+ parameters are given in the output of the show spanning-tree pvst command, as previously shown.
Conguring an EdgePort
The EdgePort feature enables interfaces to begin forwarding trac approximately 30 seconds sooner.
In this mode an interface forwards frames by default until it receives a BPDU that indicates that it should behave otherwise; it does not go
through the Learning and Listening states. The bpduguard shutdown-on-violation option causes the interface hardware to be
shut down when it receives a BPDU. When you only implement
bpduguard, although the interface is placed in an Error Disabled state
when receiving the BPDU, the physical interface remains up and spanning-tree drops packets in the hardware after a BPDU violation.
BPDUs are dropped in the software after receiving the BPDU violation.
724
Per-VLAN Spanning Tree Plus (PVST+)