Xen LRO is not disabled automatically with a bonded bridged interface with Intel X5xx 10 Gb Ethernet Adapter

A system is setup with an Intel X5xx 10 Gb Ethernet adapter card installed with the two Ethernet NIC ports bonded.  The software is configured with SLES11 XEN and using the ixgbe NIC driver.  The bonded NIC ports are attached to a bridge which is passed to a Windows guest.  The problem is manifest on operations such as Secure Copy (SCP) within the guest which fail to complete and '/var/log/messages' contains errors.

This may be fixed in a future maintenance update for SLES by automatically disabling LRO.

In the meantime, LRO can be manually disabled as follows:

Add the following to /etc/sysconfig/network/ifcfg-eth*
    ETHTOOL_OPTIONS='-K iface lro off'

where ifcfg-eth* are all of the files that correspond to interfaces in bond0.

Large Receive Offload (LRO) is disabled automatically for ethernet devices that are attached to a bridge (http://lxr.linux.no/#linux+v3.0.76/net/bridge/br_if.c#L380).

However, because bond0 provides an extra layer of abstraction between the actual NIC and the bridge, the bridging driver turns off LRO on bond0 but does not turn off LRO on eth0 and eth1 (the Intel NIC ports). Because LRO stays on, the Windows guest is unable to receive packets from the remote machine.

The workaround simply disables LRO as is intended for bridged interfaces. Eventually, a fix may automatically disable LRO on the base NIC interfaces regardless of whether they are enslaved in a bond.