Hi. I am running a XEN VM in PV mode. This VM has four cores enabled. VM network config is as follows: vif = ["ip=127.0.0.1,mac=XX:XX:XX:XX:XX:XX,bridge=br0,rate=100Mb/s"] Dom0 is dual XEON X5450 with 16GB of RAM. I can barely zmap at 10mbps ~ 12k packets/second on this VM Dec 24 16:56:43.393 [WARN] monitor: Failed to send 1502 packets/sec (998980 total failures) 13:04 0% (1d20h left); send: 9335298 11.9 Kp/s (11.9 Kp/s avg); recv: 3509 4 p/s (4 p/s avg); drops: 0 p/s (0 p/s avg); hits: 0.04% On Dom0 netback/0 utilize pretty much one core (95% CPU). While zmap is running at about 10mbps, everything starts lagging on SSH console when typing commands. I tried anything above 10mbps and I cannot no longer type at all any commands with a reasonable delay on SSH console... Dom0 is using bridged network. Is there anything that can be done to improve performance? Dom0 is attached to 1gbps network so I am 100% sure that the network is not a bottleneck. I got the following speed on Dom0 while zmap was running: Connecting to caesar.acc.umu.se (caesar.acc.umu.se)|130.239.18.142|:80... connected. HTTP request sent, awaiting response... 200 OK Length: 679477248 (648M) [application/x-iso9660-image] Saving to: `debian-7.3.0-i386-CD-1.iso' 679,477,248 20.1M/s in 23s