[CentOS] Re: Sendmail and pmtu discovery

Scott Silva ssilva at sgvwater.com
Tue Oct 14 16:40:55 UTC 2008


on 10-14-2008 6:24 AM Ralph Angenendt spake the following:
> Sean Carolan wrote:
>> We have an issue with some customers who refuse to accept ICMP traffic
>> to their mail servers.  It seems that they have put Mordac, preventer
>> of information services in charge of their firewall policy
>> (http://en.wikipedia.org/wiki/List_of_minor_characters_in_Dilbert#Mordac).
> 
> BUT ICMP IS BAD!!!!!¡¡¡¡¡
> 
>> My mail logs are showing that customers who specifically disallow ICMP
>> traffic have many "Connection Reset" entries in our logs:
>>
>> Oct 14 08:00:50 mailsrv sendmail[2024]: m9ED0Yf5002021:
>> to=<customername at customer.org>, delay=00:00:16, xdelay=00:00:16,
>> mailer=esmtp, pri=42476, relay=mail.customer.org. [XX.XX.XX.XX],
>> dsn=4.0.0, stat=Deferred: Connection reset by mail.customer.org.
>>
>> I have disabled pmtu discovery on our routers as well as on all our
>> outbound mail servers.  Is there anything else I can do on our side to
>> help the situation?
> 
> 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!

-- 
MailScanner is like deodorant...
You hope everybody uses it, and
you notice quickly if they don't!!!!

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