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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Chapter 13 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 supports the extended system ID as
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 system 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 configure multiple backup root switches. Use
the same network diameter and hello-time values as you used when you configured the primary root
switch with the spanning-tree vlan vlan-id root primary global configuration command.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
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 4094.
• (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, the switch
recalculates them.
Step 3
end Return to privileged EXEC mode.
Step 4
show spanning-tree detail Verify your entries.
Step 5
copy running-config startup-config (Optional) Save your entries in the configuration file.
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