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.4.64.0710021606550.3175@bizon.gios.gov.pl>
Date:	Tue, 2 Oct 2007 16:15:15 +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 Tue, 2 Oct 2007, Herbert Xu wrote:

> On Mon, Sep 24, 2007 at 11:44:19AM +0200, Krzysztof Oledzki wrote:
>>
>> So, with DR mode, packet goes by the lo device (with bad checksum) and
>> then get redirected outside. Unfortunately, when it leaves host it has bad
>> checksum, too. :(
>
> Did you check this by taking a tcpdump on an external host?
Yes.

> Doing a local tcpdump doesn't work as tcpdump won't show the
> correct checksum if checksum offload is enabled.
Indeed, I'm aware about this.

> If it's really sending a bogus checksum then it's a bug in
> LVS.

I'm not sure if we should call it a bug. LVS does not support such 
configuration by default - it requires kernel patching. However, it worked 
with older kernels so that's why I asked if it is possible to force full 
TCP/UDP checksum calculation?

Thank you.

Best regards,

 				Krzysztof Olędzki