NSX HostSwitch Overlay Transport Zone Limit (Error 9503)

Products

• VMware NSX

Issue/Introduction

When configuring or upgrading an ESXi host transport node in VMware NSX 4.x, the operation fails with the following validation error:

HostSwitch <HostSwitch ID> cannot participate in more than one OVERLAY transport zone, existing TZ [<existing TZ ID>] new TZ [<new TZ ID>]. (Error code: 9503)

Environment

VMware NSX

Cause

This issue occurs because NSX 4.x enforces a strict validation that limits each HostSwitch to a single Overlay Transport Zone.

• Architectural Limit: Only one vdl2 instance is created per HostSwitch. Because this instance cannot span multiple Overlay Transport Zones, the configuration is blocked.
• Version Change: In NSX-T 3.x, this configuration was not actively blocked by the UI/API, but it was never officially supported for the datapath. NSX 4.x introduced explicit validation to prevent unsupported topologies.
• VLAN Exception: A HostSwitch can still participate in multiple VLAN Transport Zones without restriction.

 

Resolution

This is a condition that may occur in a VMware NSX environment.

 

To resolve this error, you must modify the Host Transport Node configuration to ensure each HostSwitch is associated with only one Overlay Transport Zone.

Steps to Consolidate Transport Zones

1. Identify the Conflict: Review the error message to identify the two conflicting Overlay Transport Zones (the 'existing' and the 'new' TZ).
2. Consolidate Zones: Determine if the segments/workloads can be moved into a single Overlay Transport Zone.
3. Modify Host Configuration:
   • Navigate to System > Fabric > Nodes > Host Transport Nodes.
   • Select the affected host and click Edit.
   • Under the Transport Zones section, remove the excess Overlay Transport Zone.
   • Ensure only one Overlay Transport Zone remains assigned to the specific HostSwitch.
4. Verify Status: Save the configuration and monitor the Node Status until it returns to Success.

Note: If the host is part of a cluster using a Transport Node Profile (TNP), the modification must be made at the TNP level to apply to all hosts in the cluster. Perform these changes during a maintenance window if active workloads are present on the segments.

Additional Information

You may see that you are able to configure an ESXi host transport node with multiple overlay transport zones in VMware NSX-T Data Center 3.x as the check for this condition is not present. This is still an unsupported configuration and must not be used.

 

The HostSwitch can still span over multiple VLAN Transport Zones.