Disable TCP checksum offloading on KVM virtual network

Question

I have a virtual network for connecting KVM guests with the host.

I need to disable TCP checksum offloading on this network. The ethtool works fine but I want to disable it permanently and I could not find anything in virsh or QEMU documentation. Adding /etc/sysconfig/network-scripts/ifcfg-virbr1 file with the corresponding options also does not work.

The client on the virtual guest is connecting to the server running on its virtual host. When the tx checksum offloading of the host virtual network is on the client receives packets with wrong checksum. When I turn off the offloading the problem disappears. — jackhab, Mar 11 '14 at 18:17
@jackhab Weird problem. How did you notice it? I'm just curious. — Ryan Babchishin, Aug 17 '16 at 06:31
@RyanBabchishin well, I noticed HTTP requests are stuck so I looked at the traffic in Wireshark. — jackhab, Aug 17 '16 at 17:40

score 3 · Accepted Answer · edited Aug 17 '16 at 05:11

3

ethtool -K eth0 tso off in rc.local or the vm startup script. You could probably do it as a libvirt hook too

edited Aug 17 '16 at 05:11

Michael Hampton

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answered Mar 12 '14 at 01:54

dyasny

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score 2 · Answer 2 · edited Dec 16 '14 at 11:03

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I recommend doing this with a udev rule. I put this in /etc/udev/rules.d/81-bridge.rules:

ACTION=="add", SUBSYSTEM=="net", NAME=="virbr*", RUN+="/sbin/ethtool -K $env{INTERFACE} tx off"

More sophisticated approaches are possible, depending on your needs.

edited Dec 16 '14 at 11:03

Falcon Momot

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answered Dec 16 '14 at 10:43

Martin Wilck

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score 1 · Answer 3 · answered Jun 10 '22 at 01:15

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You can disable it in the guest's interface xml:

<driver>
      <host csum='off'/>
      <guest csum='off'/>
    </driver>

Refer to https://libvirt.org/formatdomain.html#setting-nic-driver-specific-options

answered Jun 10 '22 at 01:15

Yalan Zhang

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Disable TCP checksum offloading on KVM virtual network

3 Answers3