Hhhhmmmmm..... I thought my reply was private.....
Oh well,,,,,,,
What I know about ATM will fill a thimble with room left over for a skein of
yarn :->
Same for gig E
I know there are mathematical calculations for MTU in ethernet, based on
network diameter, and the physics of signal propagation through the wire. So
it may well be that if the only two stations on the wire are directly
connected and just a few feet apart, running full dup, then you can make
adjustments.
I see on my router ( 2501 ) that there is an MTU command under the ethernet
port, with values from 64 through 18000. I get an error when I try to
adjust, with a report that I don't have a 2FE port adapter.
Hmmm...... a quick look around CCO kinda indicates that the FE adapter for
the higher end routers might support a larger MTU.
And yes, while looking through the command reference, I did see MTU sizes
for various media, including ATM at 4470
Learn something every day.
Chuck
-----Original Message-----
From: Darren Ward [mailto:[EMAIL PROTECTED]]
Sent: Friday, December 01, 2000 8:29 PM
To: Chuck Larrieu; [EMAIL PROTECTED]
Subject: Re: Fast Ethernet MTU Size
Hi Chuck,
I'm not a 100% sure myself but I believe the delineation is that layer 3
fragmentation is seperate from ATM SAR.
SAR simply takes the layer 3 packet and chops it into 48 byte payloads and
reassembles it at the other end of the ATM link, the actual content of the
payload, the packet itself is irrelevant to that level.
At any rate we have seen sinificant improvements in BGP using an MTU of 4470
on
Gig and OC3 ATM so I want to try and increase the MTU on the link between
another couple of routers.
Darren
Chuck Larrieu wrote:
> Not knowing the ethernet side of things, but I am curious - and MTU of
4470
> on ATM? 53 byte cell size?
>
> I did a cursory search of the IEEE web site but didn't find much.
>
> Chuck
>
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of
> Darren Ward
> Sent: Friday, December 01, 2000 7:02 PM
> To: [EMAIL PROTECTED]
> Subject: Fast Ethernet MTU Size
>
> Hi All,
>
> Is it at all possible to raise the MTU size on Fast Ethernet?
>
> I'll give you all a scenario....
>
> ATM on one side with an MTU of 4470, fast ethernet connecting the two
> routers, Gigabit Ethernet the other side with an MTU of 4470.
>
> How can I raise the MTU of a Full Duplex Fast Ethernet Connection above
> 1500?
>
> I assume it's not possible when going through switched as they will show
> every packet as a giant but in a router to router cross-over connection
> I was hoping there was some way to keep the MTU static across the path
> rather than force the routers to fragment and re-assemble (of course the
> destination re-assembles).
>
> Darren Ward
> CCNP, CCDP, CCIE Wannabee
>
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