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Re: system/1878: MTU problem when sending mail using postfix
On Fri, 15 Jun 2001, Angelos D. Keromytis wrote:
> The following reply was made to PR system/1878; it has been noted by GNATS.
> From: "Angelos D. Keromytis" <email@example.com>
> To: firstname.lastname@example.org
> Cc: email@example.com
> Subject: Re: system/1878: MTU problem when sending mail using postfix
> Date: Fri, 15 Jun 2001 08:18:36 -0400
> Fragmented packets received by the OpenBSD box means the *peer* doesn't
> do PMTU discovery. What you're describing sounds like someone upstream
> is either filtering or not generating ICMP messages for too-large TCP
> packets. If this doesn't happen with most/all destinations, it probably
> means the remote mail server (or its network) is misconfigured.
I've seen this behaviour too when using PPPoE ADSL using /usr/sbin/ppp and
the tcpmssfixup option.
When postfix sends a:
at the end of a SMTP conversation, the status reply to the '.' is
getting lost. I don't know why this should be the case, because it
should be way less than MTU, but turning off PMTU discovery certainly
> Try ftp'ing a big file to and from that host if possible, as well as some
> other host in another network if possible.
In the case I looked at, I had no problems with bulk data transfer.
| Damien Miller <firstname.lastname@example.org> \ ``E-mail attachments are the poor man's
| http://www.mindrot.org / distributed filesystem'' - Dan Geer