Hi Dietmar,

It depends on what size frame you are trying to pass. Anything over 1504 bytes is considered "Jumbo". An MTU of 9000 would allow you to pass a 9004byte frame. If you were doing "jumbo" frames to one of your VM's and wanted double tagging you would set your physical interface with an MTU of 9004 to allow for a 9008byte frame.







On 4/18/2013 4:19 PM, Dietmar Maurer wrote:
Linux does not clearly differentiate between L2 (interface) and L3 (IP) MTU, and
also has a hidden 4 byte allowance on the interface MTU, making it confusing.
When running QinQ the parent physical interface needs a MTU of at least 1504
bytes (allows a 1508 byte frame), any sub vlan's and bridges will then inherit 
this
MTU allowing for the "inner" tag to pass externally correctly.
And what are the correct settings for jumbo frames (MTU 9000)?


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