netdev - Re: [PATCH v1 1/1] veth: Do not drop packets larger then the mtu set on the receiving side

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Message-ID: <20190111134136.GB1895@lunn.ch>
Date:   Fri, 11 Jan 2019 14:41:36 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Fredrik Gustavsson <gustfred@...il.com>
Cc:     Roopa Prabhu <roopa@...ulusnetworks.com>,
        netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Toshiaki Makita <makita.toshiaki@....ntt.co.jp>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH v1 1/1] veth: Do not drop packets larger then the mtu set
 on the receiving side

> > adding a IFF_VETH just for this seems like an overkill. especially
> > when there are other ways to indicate a virtual device type like
> > rtnetlink kind.
> > Also, its best to keep such checks local to veth, maybe with something
> > along the lines of what Andrew suggests above.
> 
> Andrew: Nice to hear that my arguments were good.

With DSA switches we somewhat rely on this behaviour, because there is
an extra header in the frame. I recently added code to automagically
increase the MTU, but that does not always work.

> For the actual use case I can not change to MTU on one of the
> interface.

Please could you explain why.

       Andrew