netdev - Re: [PATCH net] gre: Fix MTU sizing check for gretap tunnels

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Message-ID: <1373582702.4600.85.camel@edumazet-glaptop>
Date:	Thu, 11 Jul 2013 15:45:02 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Pravin Shelar <pshelar@...ira.com>
Cc:	Alexander Duyck <alexander.h.duyck@...el.com>,
	netdev@...r.kernel.org, jesse@...ira.com, davem@...emloft.net
Subject: Re: [PATCH net] gre: Fix MTU sizing check for gretap tunnels

On Thu, 2013-07-11 at 15:24 -0700, Pravin Shelar wrote:
> On Thu, Jul 11, 2013 at 1:12 PM, Alexander Duyck
> <alexander.h.duyck@...el.com> wrote:
> > This change fixes an MTU sizing issue seen with gretap tunnels when non-gso
> > packets are sent from the interface.
> >
> > In my case I was able to reproduce the issue by simply sending a ping of
> > 1421 bytes with the gretap interface created on a device with a standard
> > 1500 mtu.
> >
> > This fix is based on the fact that the tunnel mtu is already adjusted by
> > dev->hard_header_len so it would make sense that any packets being compared
> > against that mtu should also be adjusted by hard_header_len and the tunnel
> > header instead of just the tunnel header.
> >
> we can simplify code by not doing dev->hard_header_len adjustment to tunnel-mtu.
> 
> And right thing would be adjusting tunnel-mtu according to rt->dst.dev
> header-len so that we get mtu for out going path.

What's the mtu value we want to put in the ICMP message ?


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