How ARP works, and how ARP cache poisoning works

One subject beginning networking students invariably struggle with is how Layer 2 maps to Layer 3 (see http://en.wikipedia.org/wiki/Osi_model if you’re not familiar with the OSI model) using the Address Resolution Protocol, ARP. MAC lives at Layer 2, the Data Link layer, while IP addressing happens one layer up, at Layer 3. Dry facts: every network …