Originally posted by: gv
For those with a model 200 SMU upgrading to 6.5 firmware (in our case, the upgrade was from 6.1.1683.07 to 6.5.1849.35) that had been using jumbo frames on your SMU's public interface, you may notice that these stop working with the new firmware. If you try to change the MTU to anything above 1500, you'll get a "SIOCSIFMTU: Invalid argument" error.
This is due to a bug in the Intel NIC that was "fixed" in the kernel version included in the 6.5 firmware. Basically, Intel just updated the driver to no longer allow jumbo frames to avoid this bug on certain models of the 82573 Gigabit Ethernet Controller.
For more information on the bug, see [http://download.intel.com/design/network/specupdt/82573.pdf | http://download.intel.com/design/network/specupdt/82573.pdf], issue number 17 titled "ASPM/Jumbo Frames Disabled Due to Early Receive Threshold Overrun Buffer".
There is a workaround for this issue if you still need to use jumbo frames on your SMU 200. However, it involves some very deep OS hacking (and is probably not a supported operation), so I will not post details here. If you really need to do this, you may contact me in private, but you should have a good working knowledge of the Linux OS first. If anyone from the SMU team is reading this and wants details, I'll happily provide those along with some more technical info on the bug.