Hello,
When I disable the checksum offload of ethx (both in guest and host)I am not
able to reproduce the problem(received correct checksum 0xffff).
When using normal linux bridge instead of OVS, the issue is not reproducible (I
am getting proper 0xffff checksum) when I either enable or disable tx checksum
offload on guest/host eth interfaces.
Thanks & Regards,
Rakesh
________________________________
From: Jesse Gross <[email protected]>
To: Rakesh B.K <[email protected]>
Cc: "[email protected]" <[email protected]>; "[email protected]"
<[email protected]>
Sent: Thursday, August 22, 2013 4:21 AM
Subject: Re: [ovs-discuss] udp checksum issue with openvswitch
On Wed, Aug 21, 2013 at 7:09 AM, Rakesh B.K <[email protected]> wrote:
> Hello,
>
> Found the bug in OpenVSwitch and below is the Description attaching a test
> sample to reproduce the bug,
>
> Problem Description:
>
> I am facing a problem where OpenVSwitch is not complying with the RFC
> 768 standard on calculating UDP checksum. According to the standard
> (http://www.ietf.org/rfc/rfc768.txt), details on the UDP fields specify
> that
>
> "If the computed checksum is zero, it is transmitted as all ones
> (the equivalent in one's complement arithmetic)"
>
> In my case, I expect UDP checksum to be 0xffff, but I receive the
> computed checksum as 0x0000. This happens in a VM communicating
to external
> network via OpenVSwitch. For checking this, I have used udp based test
> program which is mentioned in the set-up below.
This may actually be a larger issue than just OVS, relating to the
computation of UDP checksums in software instead of hardware. Can you
try turning off hardware checksum offloading (using ethtool -K <eth>
tx off) and see if the problem happens on all packets? If it does,
then I suspect you can also reproduce the problem without OVS using
this setting.
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