42-6
Catalyst 3750 Switch Software Configuration Guide
OL-8550-02
Chapter 42 Configuring Fallback Bridging
Configuring Fallback Bridging
Adjusting Spanning-Tree Parameters
You might need to adjust certain spanning-tree parameters if the default values are not suitable. You
configure parameters affecting the entire spanning tree by using variations of the bridge global
configuration command. You configure interface-specific parameters by using variations of the
bridge-group interface configuration command.
You can adjust spanning-tree parameters by performing any of the tasks in these sections:
• Changing the VLAN-Bridge Spanning-Tree Priority, page 42-6 (optional)
• Changing the Interface Priority, page 42-7 (optional)
• Assigning a Path Cost, page 42-7 (optional)
• Adjusting BPDU Intervals, page 42-8 (optional)
• Disabling the Spanning Tree on an Interface, page 42-10 (optional)
Note Only network administrators with a good understanding of how switches and STP function should make
adjustments to spanning-tree parameters. Poorly planned adjustments can have a negative impact on
performance. A good source on switching is the IEEE 802.1D specification. For more information, see
the “References and Recommended Reading” appendix in the Cisco IOS Configuration Fundamentals
Command Reference.
Changing the VLAN-Bridge Spanning-Tree Priority
You can globally configure the VLAN-bridge spanning-tree priority of a switch when it ties with another
switch for the position as the root switch. You also can configure the likelihood that the switch will be
selected as the root switch.
Beginning in privileged EXEC mode, follow these steps to change the switch priority. This procedure is
optional.
To return to the default setting, use the no bridge bridge-group priority global configuration command.
To change the priority on a port, use the bridge-group priority interface configuration command
(described in the next section).
This example shows how to set the switch priority to 100 for bridge group 10:
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
bridge bridge-group priority number Change the VLAN-bridge spanning-tree priority of the switch.
• For bridge-group, specify the bridge group number. The range is 1
to 255.
• For number, enter a number from 0 to 65535. The default is 32768.
The lower the number, the more likely the switch will be chosen as
the root.
Step 3
end Return to privileged EXEC mode.
Step 4
show running-config Verify your entry.
Step 5
copy running-config startup-config (Optional) Save your entry in the configuration file.
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