Cisco Nexus 5500 Series Command Reference Manual page 217

Chapter S Commands
Usage Guidelines
When disabling spanning tree on a VLAN using the no spanning-tree vlan vlan-id command, ensure
Caution
that all switches and bridges in the VLAN have spanning tree 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 same
VLAN because switches and bridges with spanning tree enabled have incomplete information about the
physical topology of the network.
We do not recommend disabling spanning tree even in a topology that is free of physical loops. Spanning
Caution
tree is a safeguard against misconfigurations and cabling errors. Do not disable spanning tree in a VLAN
without ensuring that there are no physical loops present in the VLAN.
When setting the max-age seconds, if a bridge does not see BPDUs from the root bridge within the
specified interval, it assumes that the network has changed and recomputes the spanning-tree topology.
The spanning-tree root primary alters this switch's bridge priority to 24576. If you enter the
spanning-tree root primary command and the switch does not become the root, then the bridge priority
is changed to 4096 less than the bridge priority of the current bridge. The command fails if the value
required to be the root bridge is less than 1. If the switch does not become the root, an error results.
If the network devices are set for the default bridge priority of 32768 and you enter the spanning-tree
root secondary command, the software alters the bridge priority of the current bridge to 28762. If the
root switch fails, this switch becomes the next root switch.
Use the spanning-tree root commands on the backbone switches only.
Examples
This example shows how to enable spanning tree on VLAN 200:
switch(config)# spanning-tree vlan 200
This example shows how to configure the switch as the root switch for VLAN 10 with a network
diameter of 4:
switch(config)# spanning-tree vlan 10 root primary diameter 4
This example shows how to configure the switch as the secondary root switch for VLAN 10 with a
network diameter of 4:
switch(config)# spanning-tree vlan 10 root secondary diameter 4
This example shows how to configure the fex-hello-time to 10 seconds for a range of VLANs.
switch(config)# spanning-tree vlan 1-5000 fex-hello-time 10
Related Commands Command
show spanning-tree
OL-27880-02
Description
Displays information about the spanning tree state.
Cisco Nexus 5500 Series NX-OS Layer 2 Interfaces Command Reference
spanning-tree vlan
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