debug: 0.834 network: 0.810 performance: 0.792 graphic: 0.767 device: 0.713 other: 0.691 semantic: 0.655 PID: 0.655 socket: 0.638 vnc: 0.550 boot: 0.314 permissions: 0.314 files: 0.295 KVM: 0.231 udp checksum computed as 0 not converted to 0xffff, from guest os that share a common linux bridge among multiple guest os UDP checksum computed as '0' during transmission of packets that uses e1000 NIC in the Guest as well as emulated h/w in the qemu layer, That needs to be converted to 0xffff, This occurs only when Hardware checksum offload is been set in the guest OS NIC and made it as a transmitter. The guest O.S use the N/W interface that is been shared to the linux brige created in the host (used source=) in the xml tags of libvirt. As per RFC768(http://tools.ietf.org/html/rfc768 [^]), If the computed checksum is zero, it is transmitted as all ones (the equivalent in one's complement arithmetic). An all zero transmitted checksum value means that the transmitter generated no checksum (for debugging or for higher level protocols that don't care). Triaging old buck tickets ... can you still reproduce this issue with the latest version of QEMU? Is it only happening with e1000 or also with other NICs? What kind of network backend are you using (--netdev user ? tap ? ....). Could you please provide the full command line that you use to run QEMU? Thanks! Sorry, I meant "bug tickets", of course, not "buck tickets" ... need more coffee... Question is where is this zero checksum observed which is not clear from the report. If in the guest it is certainly correct. If in the host it is correct so long as the bridge appears to have checksum offloading as well. If whatever interface the guest packets appear to come from is not set up with checksum offloading this is a bug which should be fixed by setting the offload flags to match the guest. If outside the host this is a problem. Fixed: commit 0dacea92d26c31d453c58de2e99c178fee554166 Author: Ed Swierk