[c-nsp] setting max mtu on switch (Jumbo)

[-Hammer-]

One thing that I recently suffered thru regarding this is how your 
vendors define "jumbo". In a single vendor shop like Cisco, you may 
define 9000 to your end devices and 9216 to your switching to account 
for overhead. But other vendors treat jumbo differently and some (Yes, 
this is 2012) don't support it. Recently I had a multi vendor 
environment where one of the larger core vendors didn't support it. The 
result was that any performance gain from the entire solution was really 
sacrificed by the fact that one of the vendors would issue PMTUD and 
knock the frame down to 1500 regardless. Make sure you confirm the 
feature/function thru all your touchpoints and are actually going to 
benefit from it.

-Hammer-

"I was a normal American nerd"
-Jack Herer



On 5/29/2012 3:56 AM, Mark Tinka wrote:
> On Tuesday, May 29, 2012 10:40:38 AM Reuben Farrelly wrote:
>
>> I've often wondered about supposed downsides myself.  Why
>> is it that we don't see the layer 2 MTU set as high as
>> possible on Cisco devices out of the box, but a
>> relatively "normal" routing MTU set to 1500 in the
>> default config?   Are there any "bad things" that could
>> come out of this config?
>>
>> Some of the HP (Flex 10 etc) switches we run here do
>> jumbos by default and I don't think there is any way to
>> lower it. Then again these are storage switches so....
> It's probably because the only standards-based MTU value is
> 1,500 bytes, and the value for Jumbo frames has been
> recognized as a standard.
>
> As such, while all major vendors will support even up to
> 10,000 bytes in some cases, 1,500 bytes is still the 802.3
> understood standard.
>
> You can read here about how the industry is trying to adopt
> Jumbo frames as some kind of "common understanding":
>
> http://en.wikipedia.org/wiki/Jumbo_frame#Adoption
>
> Mark.
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