vSphere Distributed Switch Health Check reports unsupported VLANs for MTU and VLAN check when using IP hash teaming policy

Products

• VMware vCenter Server

Issue/Introduction

Symptoms:

• When the Health Check feature is enabled on a vSphere Distributed Switch (vDS), alarms are generated for errors with VLAN and MTU configuration.
• The monitor page for the vDS Health Check reports that some VLANs are Supported and some are Not Supported for the Physical Network Adapter under both VLAN and MTU.
• Using Route based on IP hash as Load balancing policy in vDS.

Cause

This can occur because of the combination of the Health Check protocol design and Route Based on IP hash of Load Balancing algorithm.

When Health Check starts, each host sends a broadcast frame to other hosts from their uplink and will receive a unicast frame from the other host if each frame can be reachable.

Health Check protocol determines the health status of VLAN and MTU if the uplink port which the broadcast frame was sent from can receive the unicast frame itself or not.

However, If Load balancing policy for the vDS switch port is configured as Route based on IP hash and EtherChannel is configured in the opposed physical switch, the physical switch may send the unicast frame to another uplink of host which the broadcast was not sent because of load balancing algorithm.

As a result, Health Check determines the uplink has some failure and VLAN and MTU are reported as Not Supported for the uplink.

Resolution

This is expected behavior under the configuration even though there will be no failure for the uplink port.

To determine the misconfiguration or failure of the port, please check the each configuration manually to confirm the network connection could be establish with no error.

Disable health check on the vDS after confirming that there is no misconfiguration with the load balancing.

Additional Information

Impact/Risks:
There is no data path impact.