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VMware vSAN Network Health Check for MTU check fails in a Stretched Cluster (2141733)

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Symptoms

When you have a VMware vSAN Stretched Cluster setup where vSAN Data nodes have MTU of 9000 and the Witness host/appliance is placed across the WAN which has a MTU limit of 1500, you experience these symptoms:

  • vSAN Network Health Check for MTU check in a Stretched Cluster fails
  • vSAN Network Health status shows that the Hosts large ping test (MTU check) has failed

Cause

This is an expected behavior due to the mismatch in MTUs.
 
This issue occurs because the MTU set on the vSAN Witness ESXi host/Appliance network does not match with the vSAN data node network in the vSAN cluster. vSAN Data and Witness traffic shares the same vSAN vmknic, therefore, shares a single MTU setting.


Resolution

To resolve this issue, use any one of the options:
 
  • Reconfigure the vSAN Witness host/appliance network MTU to 9000.

    Note: This may not be feasible due to WAN limitations. Consult your Network team and seek advise.

  • Change vSAN Data nodes network MTU to 1500.

    Notes:

Tags

vsan, stretched cluster, witness, mtu, network health check

See Also

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