[CentOS] Re: Sendmail and pmtu discovery

Ralph Angenendt ra+centos at br-online.de
Tue Oct 14 18:50:50 UTC 2008

Scott Silva wrote:
> on 10-14-2008 6:24 AM Ralph Angenendt spake the following:
> > So you basically broke your internet connection because of stupid
> > customers? No, there isn't anything you can do on your side -
> > especially if you don't know how large their MTU is set (which you
> > cannot discover, as they forbid you to do so). So you can only hope
> > that you get exactly the same MTU as they have (and that there is
> > nothing inbetween which has a lower MTU).
> >
> > It is their problem. If they don't want to play by the rules, they
> > should have to sit out the problems they themselves created.
> Sometimes you can't be so hard headed when you are dealing with
> customers. You usually are trying to get them to give money to YOU,
> not your competitor.
> If I told my customers that "It is your problem", I would no longer
> have customers to worry about!

But your competitor wouldn't be able to send them mails either >:)

As said, they deliberately broke their internet connection, so there isn't
much you can do except setting your MTU to an extremely low value and hope 
that there's nothing in between which has an even lower MTU.

So your best choice would be to do some consulting and give them some advice
on what they did wrong and how they can selectively block ICMP types (for 
example redirect and such).


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