James Carlson wrote:
> Garrett D'Amore writes:
>
>> I think its time someone here took a stand. 9000 bytes is a good size
>> because it is nearly universal, and is sufficient to hold an 8K NFS block.
>>
>
> "Taking a stand" here means being deliberately incompatible with some
> other vendors.
>
Only a tiny, tiny minority of vendors who for some reason think it is ok
to support a jumbo frame that is *less* than 9000 bytes. I"ve only seen
one case of that, from a very low end gigabit NIC. (Which uses around a
7K jumbo frame, I think.) I think those devices could just be
considered "incompatible" with *everyone* else. :-)
>
>> A very few devices support 16K or even higher, but the utility of such
>> large MTUs is probably somewhat limited... even at 10Gb. And the
>>
>
> What if one of these other vendors "takes a stand" on 12K just to
> spite us? Or if the IEEE itself finally decides to set a standard in
> this area and doesn't pick the same value?
>
The former would be hard, because it would be incompatible with a *lot*
of devices that simply cannot do 12K. They'd be cutting off their nose
to spite their face. The latter seems incredibly unlikely for the same
reason.
> I think we're on really shaky ground here. I completely agree with
> having a default jumbogram size, I agree with making it 9000, and I
> agree with making it "hard" to change. I don't agree that we ought to
> make it completely unchangeable just to force the issue.
>
Okay, I didn't necessarily mean to say there would *no* way to change
it, only that changing it should be something almost never done, and
only then by opening up the hood, so to speak. A choice of some value
other than 9000 is akin to choosing a different inter-packet gap
timing... there may be some unusual application for it, but I'm not sure
it deserves "first class" support (including the same level of QA
coverage!) that the reasonable default gets.
> LLDP is a much better answer to make sure there aren't undetected
> MTU-related accidents.
>
Yes, we need automatic detection here.
-- Garrett
