[c-nsp] MTU on GigE

[Alex Rubenstein]

On Sun, 6 Nov 2005, Phillip Vandry wrote:

> On Wed, Oct 19, 2005 at 02:54:47PM +0200, Vincent De Keyzer wrote:
>> So you have a "physical" MTU, and a MTU for each protocol; and no "protocol"
>> MTU can be higher than the "physical" MTU.
>
> Exception: "mpls mtu" (or "tag-switching mtu") can be larger than the
> physical interface MTU... for some reason.

Question is -- does it work?

For instance, say you have a 7206, NPE-400, running 12.0S. It has a IO-FE. 
So, int f0/0 can only have a 'mtu' of 1500, but you can set the 
'tag-switching mtu' to something much higher (say 9000).

Suppose further, that you are doing some AToM on this 7206, and the 
interface you are AToM'ing is a DS3, with a MTU of 4470.

Will it work? My limited memory remembers that this did work in one 
instance, but I can't say for sure.

I thought the MTU issue on the FE cards of cisco was a physical one -- if 
so, why does this work? What is the real reason cisco fe cards can't do 
jumbo? non-technical?


-- 
Alex Rubenstein, AR97, K2AHR, alex at nac.net, latency, Al Reuben
Net Access Corporation, 800-NET-ME-36, http://www.nac.net