Configuring The Root Bridge Id - Cisco AP775A - Nexus Converged Network Switch 5010 Configuration Manual

Configuring Rapid PVST+
This example shows how to enable STP on a VLAN:
switch# configure terminal
switch(config)# spanning-tree vlan 5

Configuring the Root Bridge ID

The software maintains a separate instance of STP for each active VLAN in Rapid PVST+. For each VLAN,
the switch with the lowest bridge ID becomes the root bridge for that VLAN.
To configure a VLAN instance to become the root bridge, modify the bridge priority from the default value
(32768) to a significantly lower value.
When you enter the spanning-tree vlan vlan_ID root command, the switch checks the bridge priority of
the current root bridges for each VLAN. The switch sets the bridge priority for the specified VLANs to 24576
if this value will cause the switch to become the root for the specified VLANs. If any root bridge for the
specified VLANs has a bridge priority lower than 24576, the switch sets the bridge priority for the specified
VLANs to 4096 less than the lowest bridge priority.
The spanning-tree vlan vlan_ID root command fails if the value required to be the root bridge is less
Note
than 1.
Caution The root bridge for each instance of STP should be a backbone or distribution switch. Do not configure
an access switch as the STP primary root.
Enter the diameter keyword to specify the network diameter (that is, the maximum number of bridge hops
between any two end stations in the network). When you specify the network diameter, the software
automatically selects an optimal hello time, forward delay time, and maximum age time for a network of that
diameter, which can significantly reduce the STP convergence time. You can enter the hello-time keyword
to override the automatically calculated hello time.
With the switch configured as the root bridge, do not manually configure the hello time, forward-delay
Note
time, and maximum-age time using the spanning-tree mst hello-time, spanning-tree mst forward-time,
and spanning-tree mst max-age configuration commands.
Procedure
Step 1
Step 2
OL-16597-01
Command or Action
switch# configure terminal
switch(config)# spanning-tree vlan
vlan-range root primary [diameter
dia [hello-time hello-time]]
Purpose
Enters configuration mode.
Configures a software switch as the primary root bridge.
The vlan-range value can be 2 through 4094 (except
reserved VLAN values.) The dia default is 7. The
hello-time can be from 1 to 10 seconds, and the default
value is 2 seconds.
Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
Configuring the Root Bridge ID
167