FT primary VM hangs due to multiple VMkernel NICs on the same subnet

Products

• VMware vSphere ESXi 8.0

Issue/Introduction

• A virtual machine with Fault Tolerance (FT) enabled experiences a hang on the FT primary node.
• The FT secondary node appears powered off.
• The vmware.log indicates a network interruption between the FT primary and secondary nodes:
  
  [YYYY-MM-DDTHH:MM:SS] In(05) vcpu-# - [vob.ftcpt.primary.reader.error] FT primary host cannot hear from secondary host.
[YYYY-MM-DDTHH:MM:SS] In(05) vcpu-# - [vob.ftcpt.remote.no.response] FT remote host (<secondary>) is not responding.

Environment

VMware vSphere ESXi 8.x

Cause

The issue occurs when multiple VMkernel interfaces are configured for FT on the same subnet on each ESXi host.

For example:

FT_vmkernel1: 192.0.2.1 / 255.255.255.0
FT_vmkernel2: 192.0.2.2 / 255.255.255.0

 

Resolution

When implementing a multiple NIC configuration for a Fault Tolerance network, assign different subnets for each VMkernel interface.

For example:

FT_vmkernel1: 192.0.2.1 / 255.255.255.0  
FT_vmkernel2: 192.0.3.1 / 255.255.255.0

Additional Information

For a similar issue, refer to: “Bad Parameter” error on Fault Tolerance with multiple NIC configuration.