[Soekris] Max MTU size

[Jed Clear]

On Mon, 29 Oct 2007, Jeff Quast wrote:
> I thought jumbo frames (gigabit nics) were for lessening interrupts.

Yes, and less checksum calculations.  However interrupt coalescing and TCP
Offload Engines make this less of an issue than it once was.

> A large frame that unpacks to many smaller frames by software (kernel).

No, typically any size frames are assembled back into one large logical
byte stream.

> It is not really 1500 bytes on the wire, is it?

Not a simple answer.  If your Path MTU supports 9k your "packets" remain
9k.  More likely you will encouter a 1500 byte MTU subnet and either have
your 9k packet fragmented or have to go throught the PMTUD process and end
up with 1500 byte packets from end to end.  But if you were asking if the
kernel or NIC breaks them down from 9k to 1500 all the time, then no.

-Jed