vSphere HA Agent on a Host Cannot Reach Management Network Addresses of Other Hosts in vCenter

Troubleshooting: vSphere HA Agent on a Host Cannot Reach Management Network Addresses of Other Hosts in vCenter

If you're encountering an issue where the vSphere High Availability (HA) agent on a specific host in your vCenter cluster cannot connect to the management network addresses of other hosts, it can prevent vSphere HA from functioning correctly. This means virtual machines (VMs) might not restart automatically in the event of a host failure. Here's a breakdown of troubleshooting steps you can take to resolve this:

1. Verify Network Connectivity:

 * Ping Tests: From the problematic host, initiate ping tests to the management network IP addresses of your vCenter Server and other ESXi hosts within the cluster. This will help determine basic network reachability.

 * vMotion Network: Ensure the network configuration used for vMotion is correct. If vMotion traffic is isolated on a dedicated VLAN, verify the VLAN settings, including switch configurations, are accurate.

 * Firewalls: Check if any firewall rules are blocking management network traffic between ESXi hosts or between vCenter and the ESXi hosts. vSphere HA relies on specific ports for inter-host communication (primarily TCP/UDP 8182).

 * Incorrect Management Network IP: Double-check the management network IP settings on the affected host. Review the subnet mask, gateway, and DNS server configurations to ensure they are correct.

 * IPv6 Usage: If you are utilizing IPv6, confirm that IPv6 is configured correctly across all hosts and that they can communicate using their IPv6 addresses.

2. Review vSphere HA Configuration:

 * Disable and Re-enable HA: In vCenter, try disabling and then re-enabling vSphere HA for the cluster. This process can trigger a reconfiguration of the HA agents.

   * Right-click the cluster in vCenter and select Settings.

   * Under Services, click vSphere Availability.

   * Click Edit, uncheck the Turn ON vSphere HA option, and click OK.

   * Click Edit again, check the Turn ON vSphere HA option, and click OK.

 * Restart HA Agent: Attempt to restart the vSphere HA agent on the problematic ESXi host.

   * Select the ESXi host in vCenter and navigate to the Configure tab.

   * Under System, select vSphere High Availability Agent. Click Restart at the top and then OK.

 * Restart Host Services: If restarting the HA agent doesn't resolve the issue, try restarting the hostd and vpxa services on the ESXi host. Connect to the ESXi Shell or via SSH and execute the following commands:

   /etc/init.d/hostd restart

/etc/init.d/vpxa restart

 * Verify Isolation Addresses: Check the configured isolation addresses (typically the default gateway) in the vSphere HA isolation response settings. Ensure the affected host can reach these addresses. If a host cannot reach its isolation addresses, it might incorrectly assume it's network isolated.

3. Additional Considerations:

 * vCenter Server Connection Status: Confirm that the affected host is properly connected to vCenter Server. If the host is disconnected, the HA agent may not function as expected.

 * DNS Configuration: Ensure that all ESXi hosts can correctly resolve the vCenter Server hostname and the hostnames of other ESXi hosts in the cluster. Proper DNS configuration is crucial for inter-host communication.

 * MTU Settings: Verify that the Maximum Transmission Unit (MTU) settings are consistent across all devices in the network path, including ESXi hosts, switches, and routers. MTU mismatches can lead to communication problems.

 * Duplicate Management Network Configuration: Check if there are multiple VMkernel adapters on the host that are checked for management traffic. This can confuse the HA agent about which network to use. Generally, it's best practice to have only one VMkernel adapter enabled for management traffic.

If you have gone through these troubleshooting steps and the issue persists, it is recommended to consult the VMware Knowledge Base or contact VMware Support for further assistance. When seeking support, be prepared to provide details about when the issue started and any relevant log information, which can help expedite the troubleshooting process.