From: Stephen Hemminger <stephen@networkplumber.org>
To: Huang Rui <huangruippp@gmail.com>
Cc: davem@davemloft.net, ast@kernel.org, daniel@iogearbox.net,
jakub.kicinski@netronome.com, hawk@kernel.org,
john.fastabend@gmail.com, kafai@fb.com, songliubraving@fb.com,
yhs@fb.com, jiri@mellanox.com, ecree@solarflare.com,
idosch@mellanox.com, petrm@mellanox.com,
alexander.h.duyck@intel.com, amritha.nambiar@intel.com,
lirongqing@baidu.com, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org, xdp-newbies@vger.kernel.org,
bpf@vger.kernel.org, roopa@cumulusnetworks.com,
nikolay@cumulusnetworks.com, bridge@lists.linux-foundation.org
Subject: Re: [PATCH] net:bridge:always disable auto-tuning when the user specified MTU
Date: Tue, 9 Apr 2019 19:39:11 -0700 [thread overview]
Message-ID: <20190409193911.2d68a64d@shemminger-XPS-13-9360> (raw)
In-Reply-To: <20190410023208.25435-1-huangruiPPP@gmail.com>
On Wed, 10 Apr 2019 02:32:08 +0000
Huang Rui <huangruippp@gmail.com> wrote:
> For example.
> My purpose is to create a bridge br0 and join eth0 into br0.
> if we use this following way, the auto-tuning flag will not be disabled.
>
> If eth0's mtu is 1200
> step 1.brctl addbr br0
> step 2.brctl addif br0 eth0
> step 3.ifconfig br0 mtu 1200
> step 4.ifconfig eth0 mtu 1500
>
> Result:
> br0's MTU: 1500, eth0's MTU: 1500
>
> Expected:
> br0's MTU: 1200, eth0's MTU: 1500
>
> I have specified br0's MTU, but auto-min policy works. So the MTU is
> not the result what we expected.
> As expected, if i have specified bridge's MTU, it will set the flag:
> BROPT_MTU_SET_BY_USER in net_bridge_opts disabled and auto-min/max
> policy will not work.But in this case, because the dev_set_mtu return
> early, the BROPT_MTU_SET_BY_USER flag will not be disabled and
> auto-min/max policy will still work.
>
> Signed-off-by: Huang Rui <huangruiPPP@gmail.com>
A bridge like this going to drop frames.
A frame received with MTU of 1200 will get dropped.
The proper way to do this is to change MTU of both interfaces to match.
next prev parent reply other threads:[~2019-04-10 2:39 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-10 2:32 Huang Rui
2019-04-10 2:39 ` Stephen Hemminger [this message]
2019-04-10 10:34 ` Petr Machata
2019-04-10 11:05 ` Nikolay Aleksandrov
2019-04-16 7:19 ` 黄睿
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