UplinkFast is enabled on a switch rather than on a port. When enabled, it
increases the bridge priority to 49,152 and adds a value of 3000 to the
spanning tree port cost of all interfaces on the switch, which makes it
unlikely that the switch will become the root switch. If bridge priority or
port cost has been manually configured on a switch, UplinkFast will not alter
those spanning tree values; it will only alter default values.
Enabling
UplinkFast affects all VLANs on the switch. You cannot configure UplinkFast on
an individual VLAN.
Configuring UplinkFast
To enable or disable UplinkFast, use this
command:

Switch(config)#[no] spanning-tree uplinkfast
[max-update-rate max_update_rate]
The
max_update_rate value represents the number of dummy
multicast packets transmitted per second when a failover occurs. The default
value is 150 packets per second (pps).
For example this is the command that would be used to enable UplinkFast with
a maximum update rate of 400 pps:
Switch(config)#spanning-tree uplinkfast max-update-rate
400
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NOTE:
UplinkFast should only be configured on access switches.
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Verifying UplinkFast
Use the show spanning-tree
uplinkfast command to verify UplinkFast configuration.
This
example shows how to identify which VLANS have UplinkFast enabled.