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Catalyst2950 and Catalyst2955 Switch Software Configuration Guide
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Chapter14 Configuring STP
Configuring Spanning-Tree Features
Beginning in privileged EXEC mode, follow these steps to configure a switch to become the root for the
specified VLAN. This procedure is optional.
To return the switch to its default setting, use the no spanning-tree vlan vlan-id root global
configuration command.
Configuring a Secondary Root Switch
When you configure a Catalyst 2950 or Catalyst 2955 switch that suppor ts the exten ded sy stem I D a s
the secondary root, the switch priority is modified from the default value (32768) to 28672. The switch
is then likely to become the root switch for the specified VLAN if the primary root switch fails. This is
assuming that the other network switches use the default switch priority of 32768 and therefore are
unlikely to become the root switch. For Catalyst 2950 switches without the extended syste m ID support
(software earlier than Cisco IOS Release 12.1(9)EA1), the switch priority is changed to 16384.
You can execute this command on more than one switch to conf igure multiple backup ro ot switches. U se
the same network diameter and hello-time values as you used when y ou co nfigured the p rima ry r oot
switch with the spanning-tree vlan vlan-id root primary global configuration command.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 spanning-tree vlan vlan-id root primary
[diameter net-diameter [hello-time seconds]] Configure a switch to become the root for the specified VLAN.
•For vlan-id, you can specify a single VLAN identified by
VLAN ID number, a range of VLANs separated by a
hyphen, or a series of VLANs separated by a comma. The
range is 1 to 1005 when the SI is installed and 1 to 4094
when the EI is installed.
•(Optional) For diameter net-diameter, specify the
maximum number of switches between any two end
stations. The range is 2 to 7.
•(Optional) For hello-time seconds, specify the interval in
seconds between the generation of configuration messages
by the root switch. The range is 1 to 10 seconds; the
default is 2 seconds.
Note When you enter this command without the optional
keywords, the switch recalculates the forward-time,
hello-time, max-age, and priority settings. If you had
previously configured these parameters, th e sw itc h
recalculates them.
Step3 end Return to privileged EXEC mode.
Step4 show spanning-tree detail Verify your entries.
Step5 copy running-config startup-config (Optional) Save your entries in the configuration file.