An administrator has enabled vSphere Distributed Switch Health Check. The hosts connected to that Distributed Switch all display an alert: - vSphere Distributed Switch MTU supported status - The admin

Raising the distributed switch MTU to 9100 would widen the gap between the VDS and the physical switch, generating a worse mismatch rather than resolving the existing alert.

Disconnecting and reconnecting the physical cable is a link-layer action that has no effect on the Layer 2 MTU value configured on either the switch or the vDS.

The vDS Health Check probes MTU consistency by sending test frames sized to the distributed switch MTU through the physical uplinks - if the physical switch discards or fragments those frames, the alert triggers. Because the VMkernel ports are set to 1600 bytes, the physical switch ports must also be configured to support at least 1600-byte frames, which directly resolves the mismatch.

Disabling the health check suppresses the notification but leaves the underlying MTU inconsistency in place, meaning oversized frames could still be silently dropped on the physical network.