Configuring A Secondary Root Bridge - Cisco nexus 5000 series Configuration Manual

Configuring Rapid PVST+
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.
SUMMARY STEPS
1. switch# configure terminal
2. switch(config)# spanning-tree vlan vlan-range root primary [diameter dia [hello-time hello-time]]
DETAILED STEPS
Command or Action
Step 1 switch# configure terminal
Step 2 switch(config)# spanning-tree vlan vlan-range
root primary [diameter dia [hello-time
hello-time]]
This example shows how to configure the switch as the root bridge for a VLAN:
switch# configure terminal
switch(config)# spanning-tree vlan 5 root primary diameter 4

Configuring a Secondary Root Bridge

When you configure a software switch as the secondary root, the STP bridge priority is modified from the
default value (32768) so that the switch is likely to become the root bridge for the specified VLANs if the
primary root bridge fails (assuming the other switches in the network use the default bridge priority of 32768).
STP sets the bridge priority to 28672.
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.
You configure more than one switch in this manner to have multiple backup root bridges. Enter the same
network diameter and hello time values that you used when configuring the primary root bridge.
OL-25842-01
Purpose
Enters global 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 NX-OS Layer 2 Switching Configuration Guide, Release 5.1(3)N1(1)
Configuring a Secondary Root Bridge
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