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Re: Is everyone else seeing duplicates?

On Wed, Dec 05, 2001 at 12:22:21PM +0100, Krzysztof Mazurczyk wrote:
> Is your mail server protected by netfilter firewall? If so, I'm suppose that
> problem of duplicating mail is caused by netfilter. Let's consider following
> scenario:
Yep, using iptables on 2.4.14 kernel running potato with Adrian Bunk's
packages for 2.4 kernels.
> 1) Remote mail server connects to local mail server and sends a mail.
> 2) Local mail server store the mail.
> 3) Mail servers exchange FIN packets.
> 4) Because of netfilter error (closing connections too early) one of FIN
> packet is dropped.
> 5) Remote server repeats transfer as it supposes that connections wasn't
> completted so mail is duplicated.
> I observe small amount of duplicated mail and dropped FIN packets which seems
> belonging to legal connections. However I haven't checked if there is
> correlation between dropped packets and duplicated mail.
> Someone would like to comment?
Yep, I think you are correct.  That seems to be exactly what was
happening.  I know that when I changed my firewall rules so that it
didn't keep on dropping these "unclean" packets then the duplicates
seemed to reduce, although I do still seem to get some.

You explained things very well there.


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