Recently, one of my colleagues was working with a customer that was intermittently getting an error on the vSAN health check in vSAN 6.6.x indicating that “A few hosts were failing ping test – large packet ping test: vsan: mtu check (ping with large packet size)”. As reported by the customer the same cluster would sometimes pass all tests in vSAN Health, and other times report the error above.

The customer enabled the vSphere distributed switch (VDS) health check and ran it on the vSphere distributed switch that was supporting the cluster. The VDS health check immediately reported …

  • Mismatched VLAN trunks between a vSphere distributed switch and physical switch.
  • Mismatched MTU settings between physical network adapters, distributed switches, and physical switch ports.

The VDS health check also reported which uplinks across the hosts had these specific misconfiguration issues, so customer had something concrete to take to his networking team to resolve the problem.

I thought this was a good example of using these two tools together to identify a networking problem and providing evidence to help facilitate the resolution.