Can I use GRO offloading with virtual guests?
Environment
- Red Hat Enterprise Linux (as KVM host)
- Red Hat Enterprise Virtualization
- Virtual guests with virtual network interfaces
Issue
- Can I implement GRO offloading on my KVM host to re-assemble fragmented packets in hardware, before passing them through the host bridge interface to my KVM guest?
Resolution
No, GRO must be off for virtualization hosts.
Turn GRO off with ethtool -K ethX gro off
If your network driver defaults to GRO on, and you need to persist this change across reboots, you can do so by following instructions at:
How do I run a script or program immediately after my network interface goes up?
Root Cause
Using GRO on a virtualization host will result in Ethernet frames being coalesced into IP packets which are larger than the MTU of the host bridge interface, of the virtual guest tap interface, and of the virtual guest interface, resulting in traffic being silently dropped.
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