Re: Comparing an old flow snapshot with some packet size data

Brian Carpenter CERN-CN <> Fri, 09 August 1996 09:03 UTC

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Subject: Re: Comparing an old flow snapshot with some packet size data
To: Andrew Partan <>
Date: Fri, 9 Aug 1996 10:40:48 +0200 (MET DST)
From: Brian Carpenter CERN-CN <>
In-Reply-To: <> from "Andrew Partan" at Aug 8, 96 03:58:00 pm
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> One question that I have been trying to figure out is 
> 	What size MTU should an ISP support on its backbone?
"Therefore, the default IP MTU for use with ATM AAL5 shall be 9180
 octets. All implementations compliant and conformant with this
 specification shall support at least the default IP MTU value for use
 over ATM AAL5." - RFC 1626

It seems "obvious" that the ISPs should if possible support at
least the largest default MTU likely to be found on user sites...


(1) it is largely irrelevant until we get rid of http 1.0

(2) Van has good arguments why larger MTUs may be a clear loser
on multi-hop TCP paths

(3) since MTU discovery is still not by any means universal,
there is a strong risk of inducing fragmentation at Internet
exchanges. Can you imagine the impact of going through the
Ethernet part of MAE East with 4k or 9k packets?

So I'd hazard a guess that it is not time to think of going
above 1500.

  Brian Carpenter