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 From:  "Neil A. Hillard" <m0n0 at dana dot org dot uk>
 To:  m0n0wall at lists dot m0n0 dot ch
 Subject:  Re: [m0n0wall] bad tcp cksum
 Date:  Tue, 3 Oct 2006 18:53:07 +0100
Hi,

        I've been away for a while and haven't seen a response to this
but apologies if I've missed it.

In message <451A397A dot 8010006 at stasoft dot ch>, Andreas Ferrari
<aferrari at stasoft dot ch> writes
>One of our customer has a VPN from his home office (wrap+m0n0 ver 1.22)
>to his office (wrap+m0n0 ver 1.22), that works fine. When he tries to
>send a mail from home over the VPN to the postfix server then the mail
>is never delivered to the mailserver.
>I noticed that small plaintext messages can be delivered to the postfix
>server but if the mail gets bigger then only the first part of the data
>are sent.
>On the mailserver i started tcpdump and could see that the mail could
>not be sent because there are a lot of bad tcp cksum messages.
>So the mailserver gets the first part right and the rest of the data
>are bad. How could that happend?

This is probably a red herring.  I suspect that you'll find that this is
due to TCP Checksum Offloading.  I spent a couple of days chasing what I
thought were problems cause by this - turns out it was something else.

HTH,


                                Neil.

-- 
Neil A. Hillard                E-Mail:   m0n0 at dana dot org dot uk