Packet loss on Extended Network unless bi-directional traffic is active - HCX

Products

• VMware HCX

Issue/Introduction

When using VMware HCX to extend networks between an on-premises data center and Azure VMware Solution (AVS), users observe significant packet loss or intermittent connectivity. This behavior typically manifests as failed pings from on-premises to AVS (or vice versa) unless traffic is initiated in both directions simultaneously.

Symptoms:

• Intermittent packet loss across extended segments.
• Connectivity is only stable when a bi-directional "double ping" is maintained.
• Unextending and re-extending the network does not resolve the issue.

 

Environment

• Product: VMware HCX 4.11.3 / VMware NSX
• Infrastructure: Azure VMware Solution (AVS)
• Networking: Distributed Virtual Switch (VDS) with Extended VLANs.

Cause

The issue is caused by a misconfiguration in the Teaming and Failover policy of the Distributed Port Group associated with the extended VLAN. Specifically, the Active and Standby uplinks are reversed or do not match the physical network uplink mapping. This causes asymmetric routing or MAC learning failures on the physical switches unless traffic is active on both paths.

Resolution

To resolve this issue, you must align the Distributed Port Group uplink configuration with the verified working physical network configuration.

Procedure: 

1. Log in to the vSphere Client.
2. Navigate to the Networkinginventory view.
3. Locate and right-click the Distributed Port Groupmatching the affected extended VLAN.
4. Select Edit Settings.
5. In the settings sidebar, select Teaming and failover.
6. Under the Uplink ordersection, verify the position of the uplinks.
7. Move the uplinks between the Active uplinksand Standby uplinks lists so they match the configuration of your functional port groups.

• Example: If the current Active uplink should be Standby, use the arrow buttons to move it to the Standby uplinks list.

8. Click OKto save the changes.
9. Test connectivity by initiating a one-way ping across the HCX extended network to verify the packet loss has ceased.