Tunnel Status is "Not Available" for multiple Transport Nodes

Products

• VMware NSX

Issue/Introduction

• Not able to view the tunnel status on the Transport Nodes. NSX UI was displaying some tunnels earlier, but are currently showing "Not Available" and keep on changing on other Transport Nodes as well.
  
  
  
• Status of the Transport node shows Up and in Success State.
• Transport Node is not in "Maintenance Mode" and have multiple Workload VMs as well.
• Verified the controller and Manager connectivity:
  On the Transport Node, we can see that both the Controller and Manager are connected successfully:
  > get managers 
> get controllers 

Environment

• VMware NSX
• NSX-T Data Center

Cause

Since DRS is enabled on the cluster, when overlay segment workloads migrate to other hosts and no overlay segment workloads remain on the affected host, the tunnel status changes to "Not available".

Resolution

This is expected behavior.

If VMs residing on overlay segments need to communicate, they must use the TEP tunnel to reach other ESX hosts and Edges for north/south communication. A host with no VMs on overlay segments will not have TEP tunnels established and will appear as "Not Available" in the NSX UI.

If VMs reside on vlan-backed segments, their communication is facilitated through standard layer 2 traffic carried by the physical infrastructure. No TEP tunnel required.

Additional Information

Please refer to the document which explain the concept of segments in NSX : VMware NSX 4.2 Documentation/Segments