Spanning tree root node has changed for Cisco Nexus

Vendor

Cisco

Description

When spanning tree is enabled, each switch device keep track of a spanning tree root node. A change of the spanning tree root node can be caused by incorrect root election priority setup or unexpected link state change or device state change. If spanning tree root node changes, Indeni will alert

Remediation Steps

Review the cause for the spanning tree root node change.

1. Execute "show spanning-tree" and "show spanning-tree summary" to identify the STP root for all the configured vlans.

2. Run "show spanning-tree vlan X detail" to collect more info about the STP topology (X=vlanid).

3. Check the event history to find where the Topology Change Notifications originate from by running "show spanning-tree internal event-history tree X brief" , (X=vlanid).

4. Display the STP events of an interface with "show spanning-tree internal event-history tree Y interface X brief" , (X=vlanid, Y=interfaceid).

5. Consider to hard code the STP root and backup root to the core switches by configuring a lower STP priority.

6. Activate the recommended vPC "peer switch" NX-OS command to a pure peer switch topology in which the devices all belong to the vPC.

7. Consider to use Root Guard feature to enforce the root bridge placement in the network. If a received BPDU triggers an STP convergence that makes that designated port become a root port, that port is put into a root-inconsistent (blocked) state.

8. For more information please review the folloing article: STP troubleshooting guide

How does this work?

This script logs into the Cisco Nexus switch using SSH and retrieves the Spanning Tree state using the "show spanning-tree" command. The output includes a complete report of the Spanning Tree state across all VLANs.

Why is this important?

This script logs into the Cisco Nexus switch using SSH and retrieves the Spanning Tree state using the "show spanning-tree" command. The output includes a complete report of the Spanning Tree state across all VLANs.

Without Indeni how would you find this?

STP Root changes do not generate syslog event. To identify STP topology changes the operator has to login to the device and use the "show spanning-tree" command to see which device is the current STP root and manually compare the previous state.


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