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Catalyst 2940 Switch Software Configuration Guide
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Chapter12 Configuring Optiona l Spa nning-Tree Features Configuring Optional Spanning-Tree Features
Beginning in privileged EXEC mode, follow these steps to enable UplinkFast. This procedure is
optional:
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 th e pa th co st r ed u ces 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.
Enabling BackboneFast (Optional)You can enable BackboneFast to detect indirect link failures and to start the spanning-tree
reconfiguration sooner.
Note If you use BackboneFast, you must enable it on all switches i n th e network. B ackb oneFast is no t
supported on Token Ring VLANs. This feature is supported for use with third-party switche s.
Beginning in privileged EXEC mode, follow these steps to enable BackboneFast. Thi s p roce dur e i s
optional:
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 spanning-tree uplinkfast [max-update-rate
pkts-per-second]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 g ener ated,
and the spanning-tree topology converges more slowly after a loss
of connectivity.
Step3 end Return to privileged EXEC mode.
Step4 show spanning-tree summary Verify your entries.
Step5 copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 spanning-tree backbonefast Enable BackboneFast.
Step3 end Return to privileged EXEC mode.
Step4 show spanning-tree summary Verify your entries.
Step5 copy running-config startup-config (Optional) Save your entries in the configuration file.