NSX Transport Nodes Show Offline with "NSX_VDL2" Overlay Tunnel Interface Down

Products

• VMware NSX

Issue/Introduction

Following a scheduled data center maintenance window, multiple NSX Host and Edge transport nodes fail to return to service, disrupting overall logical overlay network connectivity.

The following specific symptoms are observed:

• The NSX Manager User Interface (UI) explicitly displays the NSX_VDL2 overlay tunnel interface status as DOWN.

• Direct point-to-point Layer 3 connectivity (TEP-to-TEP) between local transport nodes is functional.

• Transport nodes are completely unable to ping or reach their local TEP default gateway IP.

Environment

VMware NSX

Cause

This issue is caused by a configuration omission on the upstream physical network switches during the data center maintenance window.

NSX overlay functionality completely relies on Geneve-encapsulated traffic traversing the physical network fabric over these dedicated TEP VLANs. When the physical switch infrastructure stops allowing or tagging these specific VLANs, the transport nodes become isolated from their default gateway. This breaks the external routing path required for overlay synchronization, causing the logical NSX_VDL2 tunnel infrastructure to tear down.

Resolution

To restore the transport nodes to an operational state, the physical network paths must be corrected to allow the designated TEP traffic.

Step 1: Validate Physical Infrastructure Configuration

Coordinate with your network/infrastructure team to audit the upstream physical switch configurations:

• Inspect all physical switch ports directly connected to the affected NSX Host and Edge transport nodes.

• Ensure that VLAN are explicitly added back to the allowed trunk list on those ports.

• Verify that native/tagged VLAN behaviors match the expected deployment profile on the virtual switches.

Step 2: Verify Gateway Adjacency

Once the physical network team confirms the VLANs are trunked correctly:

1. Log into the command-line interface (CLI) of an affected transport node via SSH.

2. Attempt to ping the default gateway IP:

3. Ensure that bidirectional Layer 2 and Layer 3 adjacency has recovered.

Step 3: Confirm Status in NSX Manager

Once gateway connectivity is restored, the transport nodes will automatically re-establish communication across the fabric. The NSX_VDL2 tunnel interface alerts will clear automatically in the NSX Manager UI, and the status of the nodes will return to UP.