Unable to extend HCX segment with Overlapping VLAN ID: "Error: Network was previously stretched with gateway: #.#.#.#, subnet:##. Please use the same gate for restretching."

Products

• VMware HCX

Issue/Introduction

• You are attempting to extend a second subnet and gateway using the same VLAN ID as an existing extended network that is associated with a different subnet and gateway configuration.
• The DVPG name of the existing stretched network and the DVPG name of the network to be stretched have exact same in the initial 18 characters.
• During HCX validation, it detects that the same VLAN ID has already been extended and displays a warning.
• After selecting the 'Allow Overlapping VLAN' option, the validation succeeds and HCX triggers the task to extend the network.
• The HCX task fails with the following error observed in /common/logs/admin/app.log:
  

  <timestamps> UTC [NetworkStretchService_SvcThread-####, j: ########, s: ########, , TxId: ########-####-####-####-############] ERROR c.v.v.h.n.i.AbstractJobInt- NetworkStretchJobs workflow ExtendNetworkWorkflowInt failed. Error: Network was previously stretched with gateway:###.###.###.###, subnet:##. Please use the same gate for restretching.

  Note: The gateway and subnet displayed in the logs correspond to the extended network that uses the same VLAN ID.

Cause

While stretching a network, HCX attempts to create a new segment on the target site. If the initial 18 characters of the DVPG and VLAN of the network are same between both the stretched and new DVPGs, then this would cause HCX to attempt on creating a new segment on the target site with new gateway and network, but with same network name.

This would cause a failure on the NSX side, since it already has a segment with the same name, but with different network and gateway.

Note: This is an expected behavior since we only consider up to initial 18 characters. So if all the 18 characters in the name of DVPG overlaps and the VLAN of both the DVPGs are same, only then one will hit this case.

Resolution

Change the initial characters in the name of the DVPG that needs to be stretched.