Hi All, Some more data on this, I've reproduced this on another host that's a completely stock centos/xen deployment with a centos 6.6 domU. Since I’m seeing the retransmissions on the VIF, I don't think it's related to the network stack but just in case.. Each host is connected via LACP with vlan tagging to a pair of stacked cisco 3750's. Host networking config is here: http://dpaste.com/1Q6NY3Y The vm is on br99 here. This is easily reproducable by just generating a 250mb random file and doing an scp, while watching with tshark: tshark -R "tcp.analysis.retransmission" There's no visible impact to the connection the vast majority of the time, which is why I think this has gone unnoticed. Just to confirm this wasn't related to hardware / nics, I've reproduced this on: - Dell PowerEdge M620 with broadcom nics - Dell C6220 with intel nics - Supermicro X8DTT with intel nics Any ideas? =) - Nathan