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

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Message-ID: <trinity-a9289159-8d0c-4ad1-8586-e8987e008643-1391095583899@3capp-gmx-bs16>
Date:	Thu, 30 Jan 2014 16:26:24 +0100 (CET)
From:	"Simon Schneider" <simon-schneider@....net>
To:	"Hannes Frederic Sowa" <hannes@...essinduktion.org>
Cc:	netdev@...r.kernel.org
Subject: Aw: Re: IPv4 / IPv6 over IPv4 IPsec tunnel: setting the DF bit

Hi Hannes,
thanks once again for the quick reply.

Quickly checked the ip manpage. I'm clear about the case where pmtudisc is in effect (default) - the DF bit must be TRUE in this case, for PMTUD to work.

Not sure what you meant by:

"but DF bit should get copied from inner packet up to tunnel header in every
case"

Do you mean the nopmtudisc case?

Also, IPv6 must be different then - there's no DF bit to be copied.

Could you please clarify?

best regards, Simon
 
 

Gesendet: Donnerstag, 30. Januar 2014 um 15:21 Uhr
Von: "Hannes Frederic Sowa" <hannes@...essinduktion.org>
An: "Simon Schneider" <simon-schneider@....net>
Cc: netdev@...r.kernel.org
Betreff: 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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