BGP default route missing on NSX Tier-0 Gateway

Products

• VMware NSX

Issue/Introduction

Symptoms

• Overlay workloads vms cannot communicate with external IP addresses.
• Executing get route <external-ip> on the Tier-0 Service Router returns Total number of routes: 0.
• Running get bgp neighbor summary shows the BGP session state as Estab (Established), but InPfx (Incoming Prefixes) is 0.

Environment

• VMware NSX 4.x

Cause

1. The physical TOR device is not advertising the default route or specific external prefixes to the NSX Edge nodes.
2. The Default Gateway IP address configured on the NSX Segment does not match the subnet requirements, preventing VM-to-Gateway communication.

Resolution

Review these steps to restore connectivity:

1. Verify the BGP neighbor status and prefix count from the NSX Edge CLI: Review this command before running it.
   shell

   get bgp neighbor summary

2. Confirm the routing table lacks the required destination prefix: Review this command before running it.
   shell

   get route <destination-ip>

3. Coordinate with the physical network team to ensure the TOR switch is configured to advertise the default route (0.0.0.0/0) or the specific destination prefix to the NSX BGP neighbors.
4. In the NSX Manager UI, navigate to Networking > Segments, and verify the Gateway IP/Prefix for the affected segment. Ensure it is correctly set .
5. Test connectivity from an overlay VM to the Segment Gateway, then to the external IP.

Additional Information

Troubleshooting NSX BGP