Network extension validation fails with "The IP subnet is detected on NSX_T1_GW at the target site. Duplicate extensions can cause network impact. Check Allow overlapping IP subnet to override this protection"

Products

• VMware HCX

Issue/Introduction

• The network had already been extended and was subsequently unextended.
• Re-extending the same network fails during validation with the message: 'The IP subnet is detected on NSX_T1_GW at the target site. Duplicate extensions can cause network impact. Check Allow overlapping IP subnet to override this protection.'
  
  

Environment

VMware HCX

Cause

The subnet being re-extended is already associated with the NSX_T1_GW at the target site, which is causing it to be detected as a duplicate extension.

Resolution

Check the 'Allow Overlapping VLAN' & 'Allow Overlapping IP Subnet' from optional setting in the migration wizard.

Additional Information

KB - https://knowledge.broadcom.com/external/article/396081/unable-to-extend-hcx-segment-with-overla.html