Configuring The Root Bridge Id - Cisco Nexus 7000 Series Configuration Manual

Configuring Rapid PVST+ Using Cisco NX-OS
Command or Action
Step 5
copy running-config startup-config
Example:
switch# copy running-config startup-config
This example shows how to enable STP on VLAN 5:
switch# config t
switch(config)# spanning-tree vlan 5
switch(config)# exit
switch#
Do not disable spanning tree on a VLAN unless all switches and bridges in the VLAN have spanning tree
Note
disabled. You cannot disable spanning tree on some switches and bridges in a VLAN and leave it enabled
on other switches and bridges in the VLAN. This action can have unexpected results because switches
and bridges with spanning tree enabled will have incomplete information regarding the physical topology
of the network.
Caution We do not recommend disabling spanning tree even in a topology that is free of physical loops. Spanning
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_ID primary root command, the device checks the bridge
priority of the current root bridges for each VLAN. The device sets the bridge priority for the specified VLANs
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.
Cisco Nexus 7000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.x
Configuring the Root Bridge ID
Purpose
(Optional)
Copies the running configuration to the
startup configuration.
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