Cisco Catalyst 3550 series Software Configuration Manual page 406

Configuring Optional Spanning-Tree Features
The UplinkFast feature is supported only when the switch is running PVST+. It is not supported when
the switch is running rapid PVST+ or MSTP.
Beginning in privileged EXEC mode, follow these steps to enable UplinkFast. This procedure is
optional.
Command
Step 1 configure terminal
Step 2
spanning-tree uplinkfast [max-update-rate
pkts-per-second]
Step 3
end
Step 4
show spanning-tree summary
Step 5 copy running-config startup-config
When UplinkFast is enabled, the switch priority of all VLANs is set to 49152. If you change the path
cost to a value less than 3000 and you enable UplinkFast or UplinkFast is already enabled, the path cost
of all interfaces and VLAN trunks is increased by 3000 (if you change the path cost to 3000 or above,
the path cost is not altered). The changes to the switch priority and the path cost reduces the chance that
the switch will become the root switch.
When UplinkFast is disabled, the switch priorities of all VLANs and path costs of all interfaces are set
to default values if you did not modify them from their defaults.
To return the update packet rate to the default setting, use the no spanning-tree uplinkfast
max-update-rate global configuration command. To disable UplinkFast, use the no spanning-tree
uplinkfast command.
Catalyst 3550 Multilayer Switch Software Configuration Guide
18-18
Chapter 18
Purpose
Enter global configuration mode.
Enable UplinkFast.
(Optional) For pkts-per-second, the range is 0 to 32000 packets per
second; the default is 150.
If you set the rate to 0, station-learning frames are not generated,
and the spanning-tree topology converges more slowly after a loss
of connectivity.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Configuring Optional Spanning-Tree Features
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