netdev - Re: Problems with tg3 driver after lowering the MTU

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Date:	Thu, 21 Jan 2010 16:42:07 +0100
From:	Szilveszter Ordog <slipszi@...il.com>
To:	netdev@...r.kernel.org
Subject: Re: Problems with tg3 driver after lowering the MTU

On Thu, Jan 21, 2010 at 16:27, Ben Hutchings <bhutchings@...arflare.com> wrote:
> On Thu, 2010-01-21 at 16:21 +0100, Szilveszter Ordog wrote:
>> After the MTU is lowered (e.g. to 1420) on a tg3-driven interface,
>> received packets larger than that (e.g. 1500 bytes) are silently
>> discarded by the driver. Therefore the system doesn't send ICMP
>> fragmentation-needed packets and the other side doesn't detect this
>> condition.
>>
>> Is this a known bug?
>
> I don't believe this a bug.  Within a local network, MTU should be set
> the same for all interfaces.  Routers that connect networks with
> different MTUs will generate the fragmentation-needed message as
> appropriate.

Other drivers do not behave like that. Most of them always allow
packets smaller than 1500 bytes. That is why I think that this is a
bug.

slipszi
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