[ovs-discuss] found checksum error in userspace datapath

Nacht Z NachtZ at outlook.com
Mon Nov 27 12:18:13 UTC 2017

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

                                                                                                                                         Nacht Zhuo

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