Point to Point Ethernet

William Herrin herrin-nanog at dirtside.com
Wed Jul 8 15:03:40 UTC 2009

On Wed, Jul 8, 2009 at 10:50 AM, Marshall Eubanks<tme at americafree.tv> wrote:
> On Jul 8, 2009, at 10:37 AM, Mikael Abrahamsson wrote:
>> On Wed, 8 Jul 2009, William Herrin wrote:
>>> 1. What's the point of increasing the max MTU from 9000 to 9012? If we
>>> want a higher MTU, why not just ask for one in the next standard?
>> To me the only reason for this would be to lessen overhead on small
>> packets.


At the cost of low-volume production run hardware which is A. much
more expensive (because of the low volume), B. restricted to a few
supported routers and C. less thoroughly tested. I don't see how you
come out ahead in that calculation.

>> Also, afaik standard payload MTU is 1500 for ethernet, anything
>> else is vendor extension, outside the standard.
> From what I have been told, IEEE 802 refuses to make a Jumbo frame standard,
> for backwards compatibility reasons.


My understanding is that 9000 is a standard for GigE and up but for
compatibility with earlier ethernets it's not the default. You have to
explicitly configure it and you must configure it the same on every
host and switch within the broadcast zone. For a point to point link,
this should be trivial.

Or am I mistaken?

I gather from your list that not everything which supports gige also
supports jumbo frames but that most things do.

Bill Herrin

William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004

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