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oVirt Windows guests can ping but nothing more

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25 May 2016

Actually i work on a VDI cluster based on oVirt, all of my hypervisor are linked with 2x10Gbps bond (LACP mode 4 802.3ad).
Everything is good on unix guests but with Windows guests i can’t use the network, the ping pass great but eveything bigger than 500bytes fail to transfer.

At first sight i thought it was a MTU issue but nope, MTU set to 9000 didn’t change anything.

Thanks to Alex Crow from ovirt-users mailing list, he showed me the good way, the issue is caused by LRO from slave interfaces.

LRO (Large Receive Offload) is a feature who reduce the CPU usage for receives but it’s completely incompatible with ip forwarding and routing. The result of LRO enabled and bridging could result in a low throughput or worse, a kernel panic.

To disable LRO simply use ethtool on all slave interfaces who is used in your bridges/bonds.

ethtool -K eno1 lro off

# For a permanent fix, edit the interface configuration file  
vim /etc/sysconfig/network-scripts/ifcfg-eno1

ETHTOOL_OPTIONS='-K eno1 lro off'

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