840 | Per-VLAN Spanning Tree Plus
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Modify 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 is the amount of time an interface waits in the Listening State and the Learning State
before it transitions to the Forwarding State.
• Hello-time is the time interval in which the bridge sends Bridge Protocol Data Units (BPDUs).
• Max-age is the length of time the bridge maintains configuration information before it refreshes that
information by recomputing the PVST+ topology.
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 Figure 40-4.
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.
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
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