Spanning-Tree Uplinkfast - Cisco Catalyst 2950 Command Reference Manual

Chapter 2 Cisco IOS Commands

spanning-tree uplinkfast

Use the spanning-tree uplinkfast global configuration command to accelerate the choice of a new root
port when a link or switch fails or when the spanning tree reconfigures itself. Use the no form of this
command to return to the default setting.
Syntax Description
max-update-rate pkts-per-second
Defaults
UplinkFast is disabled.
The update rate is 150 packets per second.
Command Modes
Global configuration
Command History Release
12.0(5.2)WC(1)
12.1(6)EA2
Usage Guidelines
Use this command only on access switches.
The UplinkFast feature is supported only when the switch is running per-VLAN spanning-tree (PVST).
When you enable UplinkFast, it is enabled for the entire switch and cannot be enabled for individual
VLANs.
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.
When spanning tree detects that the root port has failed, UplinkFast immediately switches over to an
alternate root port, changing the new root port directly to FORWARDING state. During this time, a
topology change notification is sent.
Do not enable the root guard on interfaces that will be used by the UplinkFast feature. With UplinkFast,
the backup interfaces (in the blocked state) replace the root port in the case of a failure. However, if root
guard is also enabled, all the backup interfaces used by the UplinkFast feature are placed in the
root-inconsistent state (blocked) and prevented from reaching the forwarding state.
78-11381-05
spanning-tree uplinkfast [max-update-rate pkts-per-second]
no spanning-tree uplinkfast [max-update-rate]
Modification
This command was first introduced.
The pkts-per-second range was changed to 0 to 65535.
(Optional) The number of packets per second at which update
packets are sent. The range is 0 to 65535.
Catalyst 2950 Desktop Switch Command Reference
spanning-tree uplinkfast
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