ESXi host displays warning: "vSphere HA agent on this host could not reach isolation address <IP Address>" in the vCenter UI

Products

• VMware vSphere ESXi

Issue/Introduction

• Summary page of an ESXi host in the vCenter UI displays a warning  "vSphere HA agent on this host could not reach isolation address <IP Address>"
  

Environment

• VMware vSphere ESXi 7.x
• VMware vSphere ESXi 8.x

Cause

The ESXi host is unable to establish network connectivity to the defined isolation IP address indicated in the error message. 

Resolution

• Verify network connectivity to the Isolation address from the ESXi. It may be necessary to check connectivity to the isolation address from a specific VMkernel Adapter.  This may vary from in individual customer environments   
• From host CLI confirm network Connectivity to the host from VMK adapter using the command below: 
  • vmkping -I vmk<#> <Isolation_Address>
    
    
• If the ping fails, it is necessary to investigate the environmental network with the help of internal Network team. 

Additional Information

• By default in a non-vSAN environment, the management gateway is used by default.  This information can be viewed from Host --> configure -->  network --> TCP/IP configuration.
• The specific isolation addresses can also be configured with custom multiple IP addresses. Refer: https://knowledge.broadcom.com/external/article/341627/
• In vSAN environments - isolation addresses work similarly. Refer: https://knowledge.broadcom.com/external/article?articleId=313763 

 

For more information on using CLI to test the connectivity Refer: Troubleshooting network and TCP/UDP port connectivity issues on Hosts

After confirming network connectivity is possible to the Isolation address from the hosts' vmk interface and the error message persists on the ESXi host, then refer: vSphere HA agent on this host could not reach isolation address '#.#.#.#', reported on ESXi host