In my previous post regarding VMWare HA isolation, I highlighted the fix when no gateway is set. However, some solutions may prevent hosts behind the firewall from pinging the gateway address. When this condition exists, the hosts will refuse to complete an HA reconfiguration properly which prevents you from migrating VMs to others hosts. You will also see the following warning in the Summary tab of all hosts within the HA cluster:
Could not reach isolation address: <xxx.xxx.xxx.xxx>
To rectify this, perform the following steps:
1. Open the vSphere Client and connect to the relevant vCenter server
2. Select the HA cluster.
3. On the Summary tab, click Edit Settings.
4. In the Settings dialog, select VMware HA and click Advanced Options.
5. In the Advanced Options (HA) dialog, enter the option name and the corresponding value:
Value: A valid IP address other than the default gateway address
Note. You can set more isolation response addresses using das.isolationaddress1 through das.isolationaddress9.
Then add the following option name and value:
Note. You must set this option if you are setting multiple isolation response addresses. Additionally you should configure das.usedefaultisolationaddress to false when the default gateway is a device which cannot be pinged.
6. Click OK.
7. Click OK.
8. Edit settings for the cluster again.
9. Disable HA and click OK.
10. Edit settings again.
11. Enable HA and click OK.
The above fix is detailed in VMware KB article 1002787.