Logical-Switch-vlan of LogicalSwitch overlapping with Logical-Switch-vlan of LogicalSwitch in same underlying Edge host-switch is not allowed. Change vlan configuration.

Products

• VMware NSX

Issue/Introduction

• In VMware NSX, Tier-1 gateway is configured with a service interface. 
• The service interface is connected through VLAN backed segment, using a specific VLAN.
• You need the same VLAN configured on a service interface on another Tier-1 gateway.
• Both Tier-1 gateways are consuming the same Edge Cluster. 
• Upon creation, the service interface is in a "Failed state".
• In the UI, you see a Realization error similar to the error below:
  ● Nov 21, 2025, 8:18:49 AM : [error_code=10048, module_name=ROUTING, error_message='[Routing] Subnet should not overlap with other logical router port of same logical router. Subnet [172.16.10.0/24] overlaps with logical router port(s) [LrPort/########-####-####-#############f9a4].', error_code=10140, module_name=ROUTING, error_message='[Routing] [Logical-Switch-vlan (654) of LogicalSwitch/########-####-####-#############d44b] overlapping with [Logical-Switch-vlan of LogicalSwitch/########-####-####-#############ac33] in same underlying Edge host-switch is not allowed. Change vlan configuration.']
  ⚬ [Routing] Subnet should not overlap with other logical router port of same logical router. Subnet [172.16.10.0/24] overlaps with logical router port(s) [LrPort/########-####-####-#############f9a4].
  ⚬ [Routing] [Logical-Switch-vlan (654) of LogicalSwitch/########-####-####-#############d44b] overlapping with [Logical-Switch-vlan of LogicalSwitch/########-####-####-#############ac33] in same underlying Edge host-switch is not allowed. Change vlan configuration.

Environment

VMware NSX

Resolution

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

If the same VLAN needs to be consumed on two Tier-1 gateways, each of the two Tier-1 gateway instances must be linked to a different Edge cluster to isolate the service interfaces within the dedicated Edge nodes. 

Otherwise (if the same VLAN on two Tier-1 gateway service interface) is not required, use a different VLAN for the other service interface. This will allow you to keep the Tier-1 gateway connected to the same Edge Cluster. 

Additional Information

For more details on creation and configuration of Tier-1 gateway, please see VMware NSX Administration Guide - Add an NSX Tier-1 Gateway.