netdev - Re: incorrect cksum with tcp/udp on lo with 2.6.20/2.6.21/2.6.22

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Message-ID: <Pine.LNX.4.64.0709232317001.24758@bizon.gios.gov.pl>
Date:	Sun, 23 Sep 2007 23:18:58 +0200 (CEST)
From:	Krzysztof Oledzki <olel@....pl>
To:	Herbert Xu <herbert@...dor.apana.org.au>
cc:	netdev@...r.kernel.org
Subject: Re: incorrect cksum with tcp/udp on lo with 2.6.20/2.6.21/2.6.22



On Sun, 23 Sep 2007, Herbert Xu wrote:

> Krzysztof Oledzki <olel@....pl> wrote:
>>
>> It seems that after some not very recent changes udp and tcp packes
>> carring data send by a loopback have incorrect cksum:
>
> This correct.  The loopback interfaces has the no checksum flag
> set so we only provide a partial checksum on output (i.e., the
> pseudoheader without the payload).
>
> We even export this to user-space via a flag.  So you should fix
> tcpdump to read this flag and ignore the checksum.

Thank you for the information. Is there any easy way to turn them on? I 
need it for LVS.

Best regards,

 				Krzysztof Olędzki