Configuring The Root Switch - Cisco Catalyst 2960-XR Configuration Manual

Configuring Spanning Tree Protocol

Configuring the Root Switch

To configure a switch as the root for the specified VLAN, use the spanning-tree vlan vlan-id root global
configuration command to modify the switch priority from the default value (32768) to a significantly lower
value. When you enter this command, the software checks the switch priority of the root switches for each
VLAN. Because of the extended system ID support, the switch sets its own priority for the specified VLAN
to 24576 if this value will cause this switch to become the root for the specified VLAN.
Use the diameter keyword to specify the Layer 2 network diameter (that is, the maximum number of switch
hops between any two end stations in the Layer 2 network). When you specify the network diameter, the
switch automatically sets an optimal hello time, forward-delay time, and maximum-age time for a network
of that diameter, which can significantly reduce the convergence time. You can use the hello keyword to
override the automatically calculated hello time.
This procedure is optional.
Beginning in privileged EXEC mode, follow these steps to configure a switch to become the root for the
specified VLAN:
SUMMARY STEPS
1. configure terminal
2. spanning-tree vlan vlan-id root primary [diameter net-diameter ]
3. end
DETAILED STEPS
Command or Action
Step 1
configure terminal
Example:
Switch# configure terminal
Step 2 spanning-tree vlan vlan-id root primary
[diameter net-diameter ]
Example:
Switch(config)# spanning-tree vlan 20-24
root primary diameter 4
Step 3 end
Example:
Switch(config)# end
OL-29424-01
Purpose
Enters the global configuration mode.
Configures 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.
Returns to privileged EXEC mode.
Catalyst 2960-XR Switch Layer 2 Configuration Guide, Cisco IOS Release 15.0(2)EX1
Configuring the Root Switch
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