From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH] veth: remove hardware checksum feature
Date: Thu, 08 Aug 2013 13:16:54 -0700
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To: Ben Greear <greearb@candelatech.com>
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On Thu, 2013-08-08 at 12:43 -0700, Ben Greear wrote:

> So, the question is:  Is there any time that I *should* be mucking with
> skb->ip_summed when bridging pkts from one device to another on modern
> kernels?  I'm using the ptype_all hook to grab packets, and ndo_start_xmit
> to send them, in case that matters.


ndo_start_xmit() is likely bypassing the core network fallbacks.

You might try dev_hard_start_xmit() instead