netdev - Re: IPv4 / IPv6 over IPv4 IPsec tunnel: setting the DF bit

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Date:	Thu, 30 Jan 2014 15:21:16 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Simon Schneider <simon-schneider@....net>
Cc:	netdev@...r.kernel.org
Subject: Re: IPv4 / IPv6 over IPv4 IPsec tunnel: setting the DF bit

On Thu, Jan 30, 2014 at 01:25:10PM +0100, Simon Schneider wrote:
> Hi,
> for the scenarios
> - IPv4 over IPv4 IPsec tunnel
> - IPv6 over IPv4 IPsec tunnel
> 
> I wonder how the DF bit of the outer (encrypted) packet is set.
> 
> There are generally three options:
> - DF bit always 0
> - DF bit always 1
> - DF bit copied from inner packet

There is a pmtudisc knob on ip tunnel ... to force DF bit on outgoing packets,
but DF bit should get copied from inner packet up to tunnel header in every
case.

Greetings,

  Hannes

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