You have a server filled with: Intel E3-1270v2, 512GB SSD, 32GB, Windows 7 64bit, 1Gbit. On this server installed VirtualBox and in it a bunch of identical machines running windows 7 32bit. Each dev to spin a simple script (python+selenium), through which the proxy connects to the same website(testing). Now to the point: when 5 running virtualnih CPU 10-20%, memory occupied 12 GB of the 32, the network 3-5 Mbps, but when you run 6 or more cars start major lag, the feeling that there is not enough network bandwidth, although this is clearly not the case, and proxies in sufficient numbers, so it is clearly not in them. Prompt, please, in what side to dig?