Chapter 6 Configuring the System
Configuring STP
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Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide
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Enabling the Port Fast Feature
The Port Fast feature brings a port directly from a blocking state into a forwarding
state. This feature is useful when a connected server or workstation times out
because its port is going through the normal cycle of STP status changes. A port
with Port Fast enabled only goes through the normal cycle of STP status changes
when the switch is restarted.
Caution
Enabling this feature on a port connected to a switch or hub could prevent STP
from detecting and disabling loops in your network, and this could cause
broadcast storms and address-learning problems.
You can modify the following Port Fast parameters:
•
Port Fast—Enable to bring the port more quickly to an STP forwarding state.
•
Path Cost —A lower path cost represents higher-speed transmission. This can
affect which port remains enabled in the event of a loop.
Enter a number from 1 to 65535. The default is 100 for 10 Mbps, 19 for
100 Mbps, 14 for 155 Mbps (ATM), 4 for 1 Gbps, 2 for 10 Gbps, and 1 for
interfaces with speeds greater than 10 Gbps.
•
Priority —Number used to set the priority for a port. A higher number has
higher priority. Enter a number from 0 to 65535.
Enabling this feature on a port connected to a switch or hub could prevent STP
from detecting and disabling loops in your network. Beginning in privileged
EXEC mode, follow these steps to enable the Port Fast feature:
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface interface
Enter interface configuration mode, and enter the port to be
configured.
Step 3
spanning-tree portfast
Enable the Port Fast feature for the port.
Step 4
end
Return to privileged EXEC mode.
Step 5
show running-config
Verify your entry.
