0. Get a Linux. 1. Read LARTC [http://www.lartc.org/ http://www.lartc.org/]. 2. Get a virtual machine hypervisor, a one that can work with a Linux bridge. KVM

0. Get a Linux. 1. Read LARTC [http://www.lartc.org/ http://www.lartc.org/]. 2. Get a virtual machine hypervisor, a one that can work with a Linux bridge. KVM/libvirt should do, as should LXC on libvirt or lxc tools (lxc-create, lxc-start and the like). Avoid Docker, as its networking is not supposed to be understood by operator. 2.5. Setup several Linux guests. Three or four should be enough to see necessary bits. 3. Try to setup different networks by hand (avoid using ifup/ifdown and their equivalents; use /(s)bin/ip, /sbin/ifconfig, and /sbin/route). 3.5 Learn how to use tcpdump (pay attention to -i option). Try understanding why some packets show up duplicated. 4. Profit. Note that in 2. you may easily replace VMs with physical machines with several network cards, but I guess it would be easier to go with VMs.