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Catalyst2950 and Catalyst2955 Switch Software Configuration Guide
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Chapter15 Configuring MSTP
Configuring MSTP Features
To return the switch to its default setting, use the no spanning-tree mst instance-id root global
configuration command.
Configuring a Secondary Root Switch
When you configure a Catalyst 2950 or Catalyst 2955 switch that suppor ts t he ext ende d syst em ID as
the secondary root, the spanning-tree switch priority is modified from the default value (32768) to
28672. The switch is then likely to become the root switch for the specified instance if the primary root
switch fails. This is assuming that the other network switches use th e de fault sw itc h p rior ity 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 conf igure multiple backup ro ot switches. U se
the same network diameter and hello-time values that you used w he n y ou co nfigured t he p ri mary r oot
switch with the spanning-tree mst instance-id root primary global configuration command.
Beginning in privileged EXEC mode, follow these steps to configure a switch as the seco nda ry root
switch. This procedure is optional.
Step3 end Return to privileged EXEC mode.
Step4 show spanning-tree mst instance-id Verify your entries.
Step5 copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 spanning-tree mst instance-id root
secondary [diameter net-diameter
[hello-time seconds]]
Configure a switch as the secondary root switch.
•For instance-id, you can specify a single instance, a range of
instances separated by a hyphen, or a series of instances
separated by a comma. The range is 0 to 15.
•(Optional) For diameter net-diameter, specify the maximum
number of switches between any two end stations. The range is 2
to 7. This keyword is available only for MST instance 0.
•(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.
Use the same network diameter and hello-time values that you used
when configuring the primary root switch. See the “Configuring the
Root Switch” section on page 15-14.
Step3 end Return to privileged EXEC mode.
Step4 show spanning-tree mst instance-id Verify your entries.
Step5 copy running-config startup-config (Optional) Save your entries in the configuration file.