Configuring The Root Bridge Id - Cisco Nexus 9000 Series Configuration Manual

Configuring the Root Bridge ID

We do not recommend disabling spanning tree even in a topology that is free of physical loops. Spanning
Caution
tree serves as a safeguard against misconfigurations and cabling errors. Do not disable spanning tree in a
VLAN without ensuring that no physical loops are present in the VLAN.
Because STP is enabled by default, entering the show running command to view the resulting configuration
Note
does not display the command that you entered to enable STP.
Configuring the Root Bridge ID
The device maintains a separate instance of STP for each active VLAN in Rapid PVST+. For each VLAN,
the network device 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-range root primary command, the device sets the bridge priority
to 24576 if this value will cause the device to become the root for the specified VLANs. If any root bridge
for the specified VLAN has a bridge priority lower than 24576, the device sets the bridge priority for the
specified VLANs to 4096 less than the lowest bridge priority.
The root bridge for each instance of STP should be a backbone or distribution device. Do not configure
Caution
an access device as the STP primary root.
With the device 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 global configuration commands.
Procedure
Step 1
Step 2
Cisco Nexus 9000 Series NX-OS Layer 2 Switching Configuration Guide, Release 7.x
102
Command or Action
config t
Example:
switch# config t
switch(config)#
spanning-tree vlan vlan-range root primary
Example:
switch(config)# spanning-tree vlan 2 root
primary
Configuring Rapid PVST+ Using Cisco NX-OS
Purpose
Enters configuration mode.
Sets the bridge priority for the spanning
tree.