[Mimedefang] Strange activity

[Jan Pieter Cornet]

On Sat, Jan 07, 2006 at 11:44:07PM +0200, Yizhar Hurwitz wrote:
> >>servers will use by default a low MTU value,
> >>for example 1300 .
> >>As far as I understand, it can only improve performance and avoid
> >>some problems with no negative side effects.
> >
> >What is the benefit of this change?  How does it improve performance?
> 
> Well, as you know, many systems nowdays use xDSL lines, that some of them 
> have lower MTU because of tunneling protocols (such as PPPoE).
> And also, many firewalls drop ICMP packets required for PMTU, so you cannot 
> trust PMTU to find the best packet size.
> Some firewalls might also drop fragment packets.
> 
> Therefore, manual tuning of MTU on Internet facing servers, can avoid 
> dropped or fragmented packets.
> I did not make a statistical research, but the logic is:
> Lowering MTU from 1500 (Ethernet default) to something in the range 
> 1300-1450 will have no negative impact (or neglectiable one) when 
> connecting with hosts that can support MTU 1500 all the way, BUT will have 
> a positive impact when connecting with hosts over lines that do need lower 
> one.

And what do you think happens when there's another host out there with
a higher MTU that wants to send you a large packet? And what if there
are DSL hosts that take your recommendation to put an MTU of 1300 on
their ethernet??

Your reasoning is flawed. Communication goes both ways, which is why we
invented standards to help us communicatie. The 1500 bytes MTU is one
standard (*1) that is meant to help us communicatie efficiently (it works
with other values, just less optimal).

If there are idiots out there that misconfigure their firewalls to block
ICMP and/or all fragmented IP then on their head it will be... I will
not bow because of such ignorance, and I will recommend others to do the
same.

An analogy to your reasoning is maybe a bit far-fetched, but goes somewhere
along the lines of:

Me: "Hmm, some people have lowered doorposts, which is inconvenient.
Especially if they don't have a sign ``Ay! See 'm Post there?!'' before
it, and thus makes you hit your head."

Yizhar: "Oh, that's easy, I just lowered _my_ doorpost to 13.00 apc (*2), So
I'm used to bowing my head before going through a doorpost... no problem".

(*1) OK it's not a standard, it's just the default on the vast majority
of the ethernet connections... so it's a de-facto standard.

(*2) apc: attoParsec.

-- 
#!perl -wpl # mmfppfmpmmpp mmpffm <pmmppfmfpppppfmmmf at fpffmm4mmmpmfpmf.ppppmf>
$p=3-2*/[^\W\dmpf_]/i;s.[a-z]{$p}.vec($f=join('',$p-1?chr(sub{$_[0]*9+$_[1]*3+
$_[2]}->(map{/p|f/i+/f/i}split//,$&)+97):qw(m p f)[map{((ord$&)%32-1)/$_%3}(9,
3,1)]),5,1)='`'lt$&;$f.eig;                                # Jan-Pieter Cornet