North-South connectivity loss during NSX Edge failover due to missing upstream routes

Products

• VMware NSX

Issue/Introduction

• Loss of North-South network connectivity occurs upon transitioning active traffic forwarding from NSX Edge 2 to NSX Edge 3.
• Traceroute analysis confirms that when Edge 3 is active, upstream physical network devices  are unable to route traffic back to the NSX environment. Connectivity is only maintained when Edge 2 is the active node.

Environment

VMware NSX

Cause

The upstream physical network infrastructure is missing return routes for the NSX logical networks specifically when Edge 3 acts as the active gateway. While NSX successfully egresses traffic, the physical underlay fails to dynamically learn or statically maintain the return routes associated with the Edge 3 peering path.

Resolution

• Engage the physical network administration team to review the routing configuration on the upstream switches.
• Verify that dynamic routing protocols (e.g., BGP peering, route redistribution) or static routes are correctly configured and established with the Edge 3 uplink interfaces, mirroring the functional configuration of Edge 2.