Re: Question regarding protocol specific mtu for FCoE

Waskiewicz Jr, Peter P
2009-06-03T21:17:17Z

> 1) the "HW MTU" used by the NIC and the guts of the driver
> 2) the legacy networking (eg IP etc) MTU passed up through the legacy path
> 3) the fcoe MTU passed up through the fcoe path
>
> where 1 is the max of 2,3

Whatever is decided to do is going to be targeted at ixgbe first. The
scenario you outlined here is exactly how ixgbe hardware works:

- Set HLREG0 to enable jumbo frames. This allows larger frames to be
accepted, but doesn't limit them to any minimum size.

- Set MHADD (for 82598) or MAXFRS (for 82599 - same register, new name) to
indicate what the absolute maximum frame size you will receive. Again,
doesn't limit the minimum size.

- The networking software can send any size up to MAXFRS (maximum frame
size) and the hardware will happily receive it and pass it up the stack.

Cheers,
-PJ Waskiewicz