Cisco Systems N3KC3064TFAL3 Configuring a Secondary Root Bridge, Procedure, Command or Action

Configuring Rapid PVST+

Configuring a Secondary 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-ageconfiguration commands.

Procedure

Command or Action

Step 1 switch# configure terminal

Step 2 switch(config)# spanning-tree vlan vlan-rangeroot primary [diameter dia [hello-time hello-time]]

Purpose

Enters configuration mode.

Configures a software switch as the primary root bridge. The vlan-rangevalue can be 2 through 4094 (except reserved VLAN values.) The dia default is 7. The hello-timecan be from 1 to 10 seconds, and the default value is 2 seconds.

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-timekeyword 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-ageglobal configuration commands.

Cisco Nexus 3000 NX-OS Layer 2 Switching Configuration Guide, Release 5.0(3)U3(1)

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