Re: system/1878: MTU problem when sending mail using postfix

["Angelos D. Keromytis" <angelos@coredump.cis.upenn.edu>]

The following reply was made to PR system/1878; it has been noted by GNATS.

From: "Angelos D. Keromytis" <angelos@coredump.cis.upenn.edu>
To: bernat@free.fr
Cc: gnats@openbsd.org
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.
 
 Try ftp'ing a big file to and from that host if possible, as well as some
 other host in another network if possible.
 -Angelos
 
 In message <20010615081200.8C000A9A9@lucas.loria>, bernat@free.fr writes:
 >
 >>Number:         1878
 >>Category:       system
 >>Synopsis:       Enabling MTU on a 2.9 box causes lost connection
 >>Confidential:   no
 >>Severity:       non-critical
 >>Priority:       low
 >>Responsible:    bugs
 >>State:          open
 >>Class:          sw-bug
 >>Submitter-Id:   net
 >>Arrival-Date:   Fri Jun 15 02:20:01 MDT 2001
 >>Last-Modified:
 >>Originator:     Vincent Bernat
 >>Organization:
 >net
 >>Release:        2.9
 >>Environment:
 >	Pentium 133, 96 Mb of RAM, dialup connection (56 Kb)
 >	System      : OpenBSD 2.9
 >	Architecture: OpenBSD.i386
 >	Machine     : i386
 >>Description:
 >	When MTU discovery is enabled, Postfix loses connection after
 >sending each mail resulting in sending the mail several time. A
 >tcpdump shows that MTU discovery doesn't work (fragmented packets come
 >back).
 >>How-To-Repeat:
 >	Enable MTU discovery and send ten mails at once
 >>Fix:
 >	Disabling MTU discovery
 >
 >>Audit-Trail:
 >>Unformatted: