Cisco Nexus 5000 Series Switch CLI Software Configuration Guide, NX-OS 4.0(1a)N1 (OL-16597-01, January 2009)

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Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
OL-16597-01
Chapter 8 Configuring Rapid PVST+
Configuring Rapid PVST+
To configure a switch to become the primary root bridge for a VLAN in Rapid PVST+, perform this task:
This example shows how to configure the switch as the root bridge for VLAN 5 with a network diameter
of 4:
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.
Note With the switch configured as the root bridge, do not manually configure the hello time, forward-delay
time, and maximum-age time using the spanning-tree mst hello-time, spanning-tree mst
forward-time, and spanning-tree mst max-age global configuration commands.
To configure a switch to become the secondary root bridge for a VLAN in Rapid PVST+, perform this
task:
This example shows how to configure the switch as the secondary root bridge for VLAN 5 with a
network diameter of 4:
Command Purpose
Step 1
switch# configure terminal
Enters configuration mode.
Step 2
switch(config)# spanning-tree vlan
vlan-range root primary [diameter dia
[hello-time hello-time]]
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.
Command Purpose
Step 1
switch# configure terminal
Enters configuration mode.
Step 2
switch(config)# spanning-tree vlan
vlan-range root secondary [diameter dia
[hello-time hello-time]]
Configures a software switch as the secondary 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.