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Date:      Mon, 7 May 2012 11:40:30 -0700
From:      Adrian Chadd <adrian@freebsd.org>
To:        Andrey Zonov <andrey@zonov.org>
Cc:        pyunyh@gmail.com, freebsd-net@freebsd.org, davidch@freebsd.org
Subject:   Re: bce: jumbo not working since r218423
Message-ID:  <CAJ-VmonY9WPcE5zVQUD2RG4BOFTD0NFF682TJ=VGDzxFfe3Mgg@mail.gmail.com>
In-Reply-To: <4FA6E03B.2000706@zonov.org>
References:  <CANU_PUGwoLSrPcGE8wT=ga3-=F_n9qN4pPXMJC%2BH72wpS9Mfcw@mail.gmail.com> <20120427230400.GB17009@michelle.cdnetworks.com> <4FA6E03B.2000706@zonov.org>

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.. I think you're misunderstanding how PMTU discovery works.

The _point_ is that you refuse to send said frame in the first place.
Any number of intermediary L2 devices may decide to drop your jumbo
TX'ed frame and not generate an ICMP error message, thus breaking PMTU
discovery anyway.

In any case, someone from broadcom piped up and pointed out that at
least for their driver, the "force strict RX MTU" is for compliance
testing.



Adrian



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