Andrea Danti - Fotolia
It's common to encounter host isolation problems when performing network maintenance, but you can avoid this issue by reconfiguring your VMware high availability cluster settings.
The hosts in your high availability-enabled cluster use a heartbeat network to determine the presence of hosts. If the master host can no longer send heartbeats and the slaves aren't receiving heartbeats or master-election traffic, then the hosts consider themselves isolated.
To prevent host isolation during network maintenance, ensure the hosts are aware of and temporarily stop the heartbeat process. There is a toggle switch for this in the cluster's settings that enables and disables host monitoring. Disable this setting during network maintenance.
Unwanted host isolation might also result if your hosts can't send a ping -- an internet control message protocol (ICMP) request -- to the isolation address or receive a response. The hosts use the default address of the default gateway for the VMkernel.
When that router doesn't respond to ICMP requests, your hosts will consider themselves isolated, even if they're still connected to the network. In this case, you need to configure the VMware high availability cluster to specify another address as an isolation address.
VMware documents a variety of parameters and possible values for a VMware high availability cluster.
It's a best practice to not rely on a single isolation address. Instead, configure an additional address on each of your management networks. This will minimize the chance your host will report host isolation.
It's also a good idea to make sure the heartbeat network itself is redundant. The easiest way to do this is to combine network interface card teaming with at least two adapters for your management VMkernel port.
You can also create an additional VMkernel network port on a second virtual switch. With this last option, the high availability feature will send additional heartbeats on that network.
Dig Deeper on VMware High Availability and Fault Tolerance
Related Q&A from Rob Bastiaansen
Centralize vCenter log files with vRealize Log Insight. Configuration with vSphere is simple and enables the centralization and transmission of event... Continue Reading
Use ESXi firewall configuration settings and VMkernel ports to control the levels of access that different services, such as Secure Shell, have to ... Continue Reading
Conservative vSphere cluster settings tell DRS to only apply the recommendations that are required for host maintenance, so you might not get any ... Continue Reading
Have a question for an expert?
Please add a title for your question
Get answers from a TechTarget expert on whatever's puzzling you.