Configuring The Root Bridge Id - Cisco nexus 5000 series Configuration Manual
Nx-os layer 2
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Also See for nexus 5000 series:
- Cli configuration manual (660 pages) ,
- Configuration manual (334 pages) ,
- Command reference manual (196 pages)
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Configuring the Root Bridge ID
DETAILED STEPS
Command or Action
Step 1
switch# configure terminal
Step 2
switch(config)# spanning-tree
vlan-range
Step 3
switch(config)# no
spanning-tree vlan-range
This example shows how to enable STP on a VLAN:
switch# configure terminal
switch(config)# spanning-tree vlan 5
Configuring the Root Bridge ID
The software maintains a separate instance of STP for each active VLAN in Rapid PVST+. For each VLAN,
the switch 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 root command, the switch checks the bridge priority of
the current root bridges for each VLAN. The switch sets the bridge priority for the specified VLANs to 24576
if this value will cause the switch to become the root for the specified VLANs. If any root bridge for the
specified VLANs has a bridge priority lower than 24576, the switch sets the bridge priority for the specified
VLANs to 4096 less than the lowest bridge priority.
The spanning-tree vlan vlan_ID root command fails if the value required to be the root bridge is less
Note
than 1.
Caution
The root bridge for each instance of STP should be a backbone or distribution switch. Do not configure
an access switch as the STP primary root.
Cisco Nexus 5000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.1(3)N1(1)
178
Purpose
Enters global configuration mode.
Enables Rapid PVST+ (default STP) on a per VLAN basis. The vlan-range value
can be 2 through 4094 (except reserved VLAN values).
(Optional)
Disables Rapid PVST+ on the specified VLAN.
Do not disable spanning tree on a VLAN unless all switches and bridges
Caution
in the VLAN have spanning tree disabled. You cannot disable spanning
tree on some of the switches and bridges in a VLAN and leave it enabled
on other switches and bridges. 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.
Do not disable spanning tree in a VLAN without ensuring that there are
no physical loops present in the VLAN. Spanning tree serves as a safeguard
against misconfigurations and cabling errors.
Configuring Rapid PVST+
OL-25842-01
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