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<p class="MsoNormal"><span lang="EN-US">Hi all:</span></p>
<p class="MsoNormal"><span lang="EN-US"> I found a question when using ovs userspace datapath without DPDK in mininet.
</span></p>
<p class="MsoNormal"><span lang="EN-US"> I found the tcp checksum is incorrect in userspace. That may means the NIC checksum offload option is useless. </span></p>
<p class="MsoNormal"><span lang="EN-US"> Here is the what I do: </span></p>
<p class="MsoNormal"><span lang="EN-US"> ```</span></p>
<p class="MsoNormal"><span lang="EN-US"> apt-get install mn # install the mininet and openvswitch </span><span lang="EN-US" style="font-size:12.0pt"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"> mn --switch ovs,datapath='user' #start mn using userspace, datapath_type=netdev
</span></p>
<p class="MsoNormal"><span lang="EN-US"> mininet > iperf #send flow from h1 to h2
</span></p>
<p class="MsoNormal"><span lang="EN-US"> ```</span></p>
<p class="MsoNormal"><span lang="EN-US"> Than I found the tcp packet both in h1 and h2, has a incorrect checksum. </span></p>
<p class="MsoNormal"><span lang="EN-US"> Then, I try to close the NIC’s offload option.</span></p>
<p class="MsoNormal"><span lang="EN-US"> ```</span></p>
<p class="MsoNormal"><span lang="EN-US"> Mininet > h1 ethtool –offload h1-eth0 rx off tx off #disable offload</span></p>
<p class="MsoNormal"><span lang="EN-US"> Mininet > h1 ethtool –offload h2-eth0 rx off tx off #disable offload</span></p>
<p class="MsoNormal"><span lang="EN-US"> ```</span></p>
<p class="MsoNormal"><span lang="EN-US"> Now the h1 and h2 can rx/tx correct-check packet. But the performance is poor.</span></p>
<p class="MsoNormal"><span lang="EN-US"> So can anyone tell me why the checksum is bad when nic offload option is enabled in userspace.</span></p>
<p class="MsoNormal"><span lang="EN-US"> By the way, I tried kernel datapath in my computer and that work fine.</span></p>
<p class="MsoNormal"><span lang="EN-US"> ```</span></p>
<p class="MsoNormal"><span lang="EN-US"> mn --switch ovs,datapath='kernel'
</span></p>
<p class="MsoNormal"><span lang="EN-US"> ```</span></p>
<p class="MsoNormal"><span lang="EN-US"> Thanks!</span></p>
<p class="MsoNormal"><span lang="EN-US"> </span></p>
<p class="MsoNormal"><span lang="EN-US"> Nacht Zhuo</span></p>
<p class="MsoNormal"><span lang="EN-US"> 2017.11.27</span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:SimSun"><o:p> </o:p></span></p>
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