From mboxrd@z Thu Jan  1 00:00:00 1970
From: Cong Wang <xiyou.wangcong@gmail.com>
Subject: Re: [Patch net v2] mlx5: fixup checksum for short ethernet frame padding
Date: Wed, 28 Nov 2018 19:53:11 -0800
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Cc: Linux Kernel Network Developers <netdev@vger.kernel.org>,
        Saeed Mahameed <saeedm@mellanox.com>
To: Eric Dumazet <edumazet@google.com>
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On Wed, Nov 28, 2018 at 7:50 PM Eric Dumazet <edumazet@google.com> wrote:
>
> On Wed, Nov 28, 2018 at 7:40 PM Cong Wang <xiyou.wangcong@gmail.com> wrote:
> >
> > On Wed, Nov 28, 2018 at 4:07 PM Eric Dumazet <edumazet@google.com> wrote:
> > >
> > > A NIC is supposed to deliver frames, even the ones that 'seem' bad.
> >
> > A quick test shows this is not the case for mlx5.
> >
> > With the trafgen script you gave to me, with tot_len==40, the dest host
> > could receive all the packets. Changing tot_len to 80, tcpdump could no
> > longer see any packet. (Both sender and receiver are mlx5.)
> >
> > So, packets with tot_len > skb->len are clearly dropped before tcpdump
> > could see it, that is likely by mlx5 hardware.
>
> Or a router, or a switch.
>
> Are your two hosts connected back to back ?

Both should be plugged into a same switch. I fail to see why a
switch could parse IP header as the packet is nothing of interest,
like a IGMP snooping.