Workload/Cluster creation fails with MTU validation error in VMware SDDC Manager

Products

• VMware SDDC Manager / VCF Installer

Issue/Introduction

• On creating a service cluster using the API or Postman, the cluster validation fails with an MTU size error. API responses or the UI will display the error message in the following format.

  The MTU <MTU> specified for the vSphere Distributed Switch <Switch_Name> is very low. The MTU should be greater than <MTU> bytes based on the traffic types defined for this switch.

• The following error message is recorded in the SDDC logs:

  The MTU <MTU> set for the VDS <VDS_Name> is not valid. MTU should be at least <Minimum_MTU_Value>

• During the workload addition workflow the task failed at vMotion validation with the error : 

  ESX Host <Host_FQDN> vmkping from <vMotion IP> to <vMotion IP> VLAN <vMotion_VLAN> doesn't support MTU 9000 for network 'VMOTION' but smaller 1500 MTU packet passes

Environment

VMware SDDC Manager 9.x

Cause

This is an expected behavior. It occurs because the MTU defined for the virtual switch is smaller than the MTU of the underlying networks, such as NFS or vMotion.

Resolution

To resolve this issue, review and adjust the network design using one of the following approaches.

• Validate the physical switch and the physical network has MTU set to 9000 or above. 
• Change the MTU of the affected distributed virtual switch to be equal to or greater than the maximum MTU required by the assigned traffic types, for example, 9000.
• Change the MTU of specific networks, such as NFS or vMotion, to match the distributed virtual switch MTU of 1500.
• Separate the traffic by creating one distributed virtual switch with an MTU of 1500 for management traffic, and another distributed virtual switch with an MTU of 9000 for storage or vMotion traffic.

Additional Information

Japanese version: VMware SDDC Manager にて MTU 検証エラーによりクラスタ作成が失敗する(430689)