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Maximum number of VMkernel interfaces per ESXi host

I received was asked what the maximum number of VMkernel interfaces per ESXi host was. Off the top of my head I was not aware of one so I consulted the vSphere 5.1 Configuration Maximums guide. The guide did list any VMkernel maximums.
So is the answer unlimited?

Well, to create a vmknic you must create a portgroup. For example, in ESXi 5.1 you can run the following commands:

Per the vSphere 5.1 Configuration Maximums guide you can have:

  • A maximum of 256 portgroups per standard switch. This means you should be able to create up to 256 vmknics per standard switch.
  • A maximum of 256 ephemeral port groups per vCenter (not recommended per http://kb.vmware.com/kb/1022312). This means you should be able to create up to 256 vmknics per host.
  • A maximum of 10,000 static portgroups per distributed switch. However, per esxcli it appears you are only allowed up to 256 vmknics (see comments after -i flag below) per host.

I tested on an ESXi 5.1 host using the standard switch and I was only able to make it to 125 vmknics before running into an “Out of resources” errors:

Looking at /var/log/vmkwarning.log I saw:

The error code returns:

Next, I ran the same test on the distributed switch and made it to over 256 vmknics without issue. Does this mean that the distributed switch can have more VMkernel interfaces than the standard switch? Not so fast! I was almost thrown off by this as well until I remembered the default number of ports configured on a vSwitch is 128 (http://kb.vmware.com/kb/1008040). Upon increasing the number of ports on the standard switch and rebooting the host, repeating the test resulted in the same results as the distributed switch.
So back to the original question, what is the maximum number of VMkernel interfaces per ESXi host? The answer from a VMkernel perspective is unlimited. The real limits are those imposed in the vSphere 5.1 Configuration Maximums guide being:

  • 256 port groups per standard switch (if applicable)
  • 1050 active ports per host (VDS and VSS)

In both cases, I believe the limits specified are “soft” support maximums and not “hard” enforced maximums. At the end of the day, I cannot think of any reason why you would need more than a dozen VMkernel interfaces so all you need to know is that you should not hit any known limit.

© 2013, Steve Flanders. All rights reserved.

Published inVMware

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