[ovs-discuss] udp checksum issue with openvswitch

[Jesse Gross]

On Wed, Aug 21, 2013 at 7:09 AM, Rakesh B.K <bk.rakesh at ymail.com> 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.