Jumbo Frames, MTU 9000 or 9216?

[Boudewijn Plomp]

Hi,

There are several blogs and white papers that describe how to configure QoS and Jumbo Frames. But they differ in therms of MTU size. Most official UCS based white papers configure an MTU size of 9000. What is best-practice for a FlexPod? Configure UCS, Nexus and NetApp all with MTU 9000? And, is there is reason for this? (e.g. 6x1500=9000 for fragmentation)

I hope this is not a stupid question but I have seen I am not the only one who is confused about it.

Thanks,

Boudewijn

[davidng]

Boudewijn,

There are several places you need to set the MTU size of and the max MTU is allowed.  Within the UCS system itself, the MTU configuration needs to be done at the FI and vNIC.  The max MTU allowed is 9216 and 9000 respectively.  The FI MTU should never be less than the MTU size of the endpoints.   Just remember, the FI is a simple L2 device and doesn't do any fragementation.  Therefore, it is okay to set the MTU on the FI to 9000 but no harm at setting it at 9216 in case of any padding added by OS, intermediary devices (vFW, vRouters, etc), etc.

Hope this helps,

David Nguyen