[c-nsp] drawbacks of enabling higher MTU sizes/ jumbo frames onCatalysts?

[sthaug at nethelp.no]

> anyone has any real- life experience of whether enabling
> jumbo frames on, say, a 3750 will hurt the performance of
> the switch? (buffers come to mind)

We have run several 3750 (with 24 10/100/1000 ports and 4 SFP ports)
and the corresponding 3560 model with 9000 jumbo MTU with no apparent
ill effects. Seems to work just fine. Note that if you enable a large
"system jumbo MTU" (eg. 9000), you *also* want to enable a "system MTU"
of 1546 - even if the box has *no* 10/100 ports! If you don't, it'll
complain like this:

Mar 21 19:36:29.431 UTC: %DOT1Q_TUNNELLING-4-MTU_WARNING: 
System MTU of 1500 might be insufficient for 802.1Q tunnelling.
802.1Q tunnelling requires system MTU size of 1504 to handle maximum
size ethernet frames.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no