Hello, I am facing a segmentation issue in xen and I hope that I can get some advices here. There are two physical computers with ubuntu 14.04 installed. One of them is running xen 4.4 also with ubuntu 14.04 guests. I did not change any network offloading, based on the parameters I would expect packets up to 64k on the interfaces (only LRO is disabled). When I was testing with iperf (TCP), I can see these large packets on all the way during the communication when I am performing it between 2 guests, from a guest to the other computer, even from the other computer to the dom0. The only case which shows strange behaviour is when I am running the iperf server on a guest and the client on the other physical computer. In this case in can see the large packets on the physical interfaces but on the vif interface I can see that most of the packets are ~MTU sized (1448). Actually it seems that if the packet is larger than ~25k on the physical side then it is segmented into MTU sized packets (by the netback?). With iperf it is actually almost always true without changing the buffer size of the client. I checked that the same happens with linux bridge and open vSwitch. I also updated the kernel of dom0 and the guest up to 3.15 without any luck. Thank You in advance! Daniel