Intermittent connectivity issue between the Supervisor VM and ESXi hosts

Products

• VMware NSX

Issue/Introduction

• VCF 9 is installed with NSX networking.
• VKS is used with VCF Networking with VPC stack deployed.
• Ping from Supervisor VM to ESX hosts fails for half the hosts in the cluster.
• Packet captures show that traffic reaches the ESX host and a reply is sent back through T0.
• T0 shows multiple routes to the Supervisor subnet.
  
  

  edge(tier0_sr[X])> get route

  Total number of routes: X
> * 172.16.0.0/24 [3/0]  via 100.64.0.1, linked-x 
> * 172.16.0.0/24  [3/0] via 100.64.0.2, linked-x, 

• Multiple VPCs exist within environment with overlapping subnets for the Supervisor.
• Both VPCs are connected to the same T0

Environment

VMware NSX 9

Cause

The IPAM workflow correctly allocates non-overlapping subnets within each block independently. If both blocks cover the same address range, the IPAM allocations from the two blocks will produce overlapping subnets across VPCs. When public subnets are created, the connected route is advertised from each TGW's VRF to the T0 via inter-VRF static routes.The T0 sees two equal-cost paths for the same prefix. This enables ECMP. As the Supervisor is only connected to a single VPC, traffic is dropped when sent to second route.

Resolution

Remove the overlapping segment/subnet from the VPC where the Supervisor is not connected.