10Gb vMotion - 9000 MTU on vSwitch, 8982 MTU on Port Group Limit

Hello all,

We've been doing some testing for a new infrastructure. We're using 10Gb ethernet (Force 10's) and we noticed something very strange.

Per Scott Lowe's blog I was pretty sure you would set the MTU to 9000 on both the vSwitch and the Port Group

http://blog.scottlowe.org/2009/05/21/vmware-vsphere-vds-vmkernel-ports-and-jumbo-frames/

However, what we noticed was that if we went over 8982 MTU on the port group vMotion failed. We were able to reproduce this time and time again.

I'm not sure why VMware would have this limitation. I know the MTU on the FOrce10 switch isn't the issue because we can actually turn that all the way up to a 12,000 MTU. This seems something related to VMware specifically.

Any thoughts our ideas?

Thank you kindly,

Steven