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Re: skb_checksum_help

To: tgraf@xxxxxxx (Thomas Graf)
Subject: Re: skb_checksum_help
From: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Date: Mon, 24 Jan 2005 12:31:34 +1100
Cc: kaber@xxxxxxxxx, david@xxxxxxxxxxxxxxxx, netdev@xxxxxxxxxxx
In-reply-to: <20050124005348.GL23931@xxxxxxxxxxxxxx>
Organization: Core
Sender: netdev-bounce@xxxxxxxxxxx
User-agent: tin/1.7.4-20040225 ("Benbecula") (UNIX) (Linux/2.4.27-hx-1-686-smp (i686))
Thomas Graf <tgraf@xxxxxxx> wrote:
> Call Trace:
>  [<c02b7c86>] dev_queue_xmit+0x246/0x290
>  [<c02e79c0>] ip_finish_output+0x0/0x1f0
>  [<c02e65d0>] ip_forward_finish+0x0/0x50

Something is screwed up here.  If the packet really went
through forwarding, then skb->ip_summed should be CHECKSUM_NONE.
This is done as the first thing in ip_forward().

So if you're seeing CHECKSUM_HW at the end of the pipe,
then somebody must've changed it.  CHECKSUM_HW should
only be seen in dev_queue_xmit for locally generated

I suggest that you print out the value of skb->ip_summed
at various points in and after ip_forward() to find out
who is changing skb->ip_summed.

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