Host Preparation Failure: VTEP Installation Incomplete and Host in Partial Success State.

Products

• VMware NSX

Issue/Introduction

• Host configuration failed with below error
  
  Host configuration: VTEP [vmk11, <IP address>] failed to be applied: Failed to add VTEP: {'fault': 'PlatformConfigFault', 'msg': 'An error occurred during host configuration.', 'faultMessage': ['Operation failed, diagnostics report: Unable to Set: Network unreachable: VSI node (480:VSI_NODE_net_tcpip_instances_vNics_v4_gateway)']}
  
• Analysis of the host's vmkernel logs reveals that one of the VTEP interface is inadvertently configured to point to an incorrect gateway address

Environment

NSX 3.x
NSX 4.x

Cause

The root cause is a gateway mismatch for VTEPs when a single TEP IP Pool contains multiple subnets and IPs from one subnet are exhausted, forcing subsequent VTEPs to pull IPs from another subnet within the same pool. The VXLAN netstack can only maintain a single default gateway for TEPs, which is derived from the first acquired subnet, leading to network unreachability for TEPs whose IPs belong to a different subnet. This behavior is considered a design limitation, not a defect.

Resolution

• Do not configure TEP Pool with multiple IP subnets
• Ensure there are sufficient IP address available in the subnets when applying the TNP to cluster