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Date:      Tue, 21 Apr 2020 10:17:54 -0500
From:      Tim Daneliuk <>
To:        FreeBSD Mailing List <>
Subject:   Re: More On FreeBSD Network Speed (Was: Changes To nat-ing Behaviour?)
Message-ID:  <>
In-Reply-To: <>
References:  <> <>

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On 4/21/20 8:15 AM, Tim Daneliuk wrote:
> On 4/20/20 3:00 PM, Tim Daneliuk wrote:
>> Linux and FreeBSD have superframe MTUs of 9000 set MacOS MTU is set to 1500.
> For anyone else that may run into this:  For reasons unclear to me,
> FreeBSD hated that the Linux box was forcing an MTU of 9000, even though
> FreeBSD had the same thing set.  The fix was to tell Linux to use
> automatic MTU negotiation and all was well.  Interestingly, when I did
> this, Linux decide 1500 was the right size and performance came back.
> Go figure...

This seems to be a Debian thing only.  If I set the MTU to 9000 on a CentOS7
box, it works just fine with FBSD.  But two different  Debians (raspbian
and linuxmint) show severely degraded network performance against FBSD
(and only FBSD) when their MTUs are set to 9000.

At this point, the problem is fixed, but I would just love for an IP
internals expert to explain why this might be happening only viz

Tim Daneliuk
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