If you are running ESXi 6.5 with IPv6 disabled, you are at risk of a host failure with PSOD. VMware recently updated KB2150794 "ESXi 6.5 host fails with PSOD when IPV6 is disabled" with the latest information about this problem. The KB also includes a detailed example of a backtrace you may see if your ESXi host fails for this reason.
The only current workaround is to enable IPv6.
Note: For a certain period in July 2018 VMware claimed in the KB that the issue was resolved in ESXi 6.5 Update 1, however they retracted this message soon after.
As IPv6 has gradually gained popularity, VMware decided to enable it in the default host configuration (since ESXi 5.1).
Why would you disable IPv6 on ESXi? As a fellow VCDX and blogger Andrea Mauro suggested, there may be different reasons:
Several people are disabling IPv6 support in ESXi for different reasons: because of the minimum privilege principle (if you are not using a service, why you have to keep it enabled?) or simple because they don’t want any IPv6 address in the network.
Andrea Mauro, ESXi Networking - Disable IPv6?
There are not many reasons for disabling IPv6 on ESXi, but I would add one more. There is a VMware KB article 2108130 that actually recommends disabling IPv6. This one affects ESXi 5.5 before Patch 4 and subsequently you would be at risk of a PSOD if you have IPv6 enabled. If you established a configuration policy in your environment to always disable IPv6 on ESXi for that reason, you are likely to have done it for 6.5 as well.
Both of these KBs are reported in Runecast Analyzer. You can use the Analyzer to automatically detect whether you are affected, and where, based on your IPv6 status and host versions:
Figure 1: IPv6 KBs in Runecast Analyzer
So, if you run ESXi 6.5, prior to Update 1, you need to ensure IPv6 is enabled (which is the default setting). If you need to enable it then you can employ various methods:
Select the ESXi host and navigate to:
Configure > Networking > Advanced
Click the Edit button and select Enabled from the dropdown menu.
Figure 2: Enabling IPv6 for ESXi in vSphere Web Client (Flash)
The screenshot above shows you the configuration location in the Flash version of the Web Client. In the latest Web Client versions, you can also use the HTML5 client to access the Advanced Networking configuration.
You can also use CLI to enable IPv6 for ESXi:
Set-VMHostNetwork -Network (Get-VMHostNetwork -VMHost $hostname) -IPv6Enabled
where $hostname is the ESXi host name where you want to enable IPv6
esxcli network ip set --ipv6-enabled=true
You can also use the DCUI console to enable/disable IPv6
Note: Changes will only take effect after an ESXi host reboot.
Do you have IPv6 disabled on your ESXi hosts for a reason? Let us know on Twitter.