VMware vSphere HA: Adding Additional Isolation Addresses


VMware’s vSphere HA can be found in nearly every data center. In short, HA provides a means for virtual machines to restart on functioning hosts in the event that their current host fails. It’s cool stuff that will save the day in the event of a hardware failure (on the host side, at least). But it also has another role: determining whether an isolation event exists.

Isolation events occur when hosts within an HA cluster lose connectivity to either the network or other hosts in the cluster. We’ve got three options to select from, in order to tell the host how to deal with its VMs: Leave Powered On, Shutdown, and Power Off.

By default, vSphere HA will use the default gateway for its management network as the default isolation address. However, you are able to specify additional isolation addresses for the host to ping to determine whether an isolation response should be triggered. A common and practical design is to include the IP address(es) of your IP-based storage as additional isolation addresses. The goal is to provide enough additional isolation addresses to all but rule out the likelihood of a false positive (and therefore an unnecessary isolation response).

To set these additional isolation addresses, use the following syntax in the Advanced Options screen for your cluster settings:


You can configure up to 10 addresses (0-9).

For anyone running a lab on a disconnected network, you’ll probably notice that vSphere HA cannot ping the default isolation address (well, if you’ve got no default gateway, that is). In this case, you’ll want to use an additional advanced option: das.usedefaultisolationaddress. Set this to false, then use the das.isolationaddress0 option to specify a valid address on your lab network.

Hope this helps!

2 responses to “VMware vSphere HA: Adding Additional Isolation Addresses

  1. In case of multiple isolation addresses, when the HA agent could reach the one of the addresses in between will it continue to check for next address or it stops there.

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Nick Kelly

Cybersecurity Engineer, Cisco

Nick has over 20 years of experience in Security Operations and Security Sales. He is an avid student of cybersecurity and regularly engages with the Infosec community at events like BSides, RVASec, Derbycon and more. The son of an FBI forensics director, Nick holds a B.S. in Criminal Justice and is one of Cisco’s Fire Jumper Elite members. When he’s not working, he writes cyberpunk and punches aliens on his Playstation.


Virgilio “BONG” dela Cruz Jr.

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Field Solutions Architect, Tech Data

Virgilio “Bong” has sixteen years of professional experience in IT industry from academe, technical and customer support, pre-sales, post sales, project management, training and enablement. He has worked in Cisco Technical Assistance Center (TAC) as a member of the WAN and LAN Switching team. Bong now works for Tech Data as the Field Solutions Architect with a focus on Cisco Security and holds a few Cisco certifications including Fire Jumper Elite.


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John is our CTO and the practice lead for a talented team of consultants focused on designing and delivering scalable and secure infrastructure solutions to customers across multiple industry verticals and technologies. Previously he has held several positions including Executive Director/Chief Architect for Global Network Services at JPMorgan Chase. In that capacity, he led a team managing network architecture and services.  Prior to his role at JPMorgan Chase, John was a Distinguished Engineer at Cisco working across a number of verticals including Higher Education, Finance, Retail, Government, and Health Care.

He is an expert in working with groups to identify business needs, and align technology strategies to enable business strategies, building in agility and scalability to allow for future changes. John is experienced in the architecture and design of highly available, secure, network infrastructure and data centers, and has worked on projects worldwide. He has worked in both the business and regulatory environments for the design and deployment of complex IT infrastructures.