Error: vSAN Cluster Formation Fails After Host Rebuild Networking Errors.
Article ID: 451285
Updated On:
Products
Issue/Introduction
Rebuilding an ESXi host can sometimes break vSAN cluster formation. You'll usually see this when a new host has an outdated or empty unicast agent list, leaving it unable to talk to the other nodes. If the networking stack changed during your rebuild, the cluster won't just "fix itself." You need to manually verify the unicast settings via the CLI to get the hosts back in sync.
Symptoms :
- Host rebuild completes but the node remains isolated.
- vSAN health check reports "Network connectivity issues" or "Unicast agent not configured."
- The cluster fails to form even if physical connectivity is verified.
Environment
VMware vSAN 8.0.x
VMware vSphere ESXi 8.0.x
Cause
This issue occurs when the vSAN unicast agent list is not correctly populated on the hosts, or when previous configuration states persist on a rebuilt host, preventing it from communicating with the existing cluster members.
Resolution
To resolve this issue, manually join the host to the cluster and verify the unicast agent configuration:
- Log in to the ESXi host via SSH.
- Retrieve the Sub-Cluster UUID from an existing healthy host in the cluster:
esxcli vsan cluster get - Manually join the problematic host to the cluster using the UUID obtained in step 2:
esxcli vsan cluster join -u ####-####-####-#### - Verify the unicast agent list and add any missing neighbors if necessary:
esxcli vsan network unicastagent list - Refresh the vSphere Client and verify the cluster health is green.
Additional Information
- For steps on configuring vSAN Unicast networking via CLI, see Configuring vSAN Unicast networking from the command line.
- If you are still seeing network partitions or the host refuses to join after updating the unicast list, please review our guide on how to open a technical support case : Contact Broadcom support
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