netdev - Re: [PATCH] sit: allow ip fragmentation when using nopmtudisc to fix package loss

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Message-Id: <20090828.235404.61171174.davem@davemloft.net>
Date:	Fri, 28 Aug 2009 23:54:04 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	contact@...chahlusiak.de
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] sit: allow ip fragmentation when using nopmtudisc to
 fix package loss

From: Sascha Hlusiak <contact@...chahlusiak.de>
Date: Tue, 25 Aug 2009 12:48:42 +0200

> if tunnel parameters have frag_off set to IP_DF, pmtudisc on the ipv4 link
> will be performed by deriving the mtu from the ipv4 link and setting the
> DF-Flag of the encapsulating IPv4 Header. If fragmentation is needed on the
> way, the IPv4 pmtu gets adjusted, the ipv6 package will be resent eventually,
> using the new and lower mtu and everyone is happy.
> 
> If the frag_off parameter is unset, the mtu for the tunnel will be derived
> from the tunnel device or the ipv6 pmtu, which might be higher than the ipv4
> pmtu. In that case we must allow the fragmentation of the IPv4 packet because
> the IPv6 mtu wouldn't 'learn' from the adjusted IPv4 pmtu, resulting in
> frequent icmp_frag_needed and package loss on the IPv6 layer.
> 
> This patch allows fragmentation when tunnel was created with parameter
> nopmtudisc, like in ipip/gre tunnels.
> 
> Signed-off-by: Sascha Hlusiak <contact@...chahlusiak.de>

Seems reasonable, applied to net-next-2.6, thanks!
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