ARP Spoofing & MITM Fundamentals

ARP is the protocol that maps an IP to a MAC address on the local network, and it was designed in an era when nobody on the wire was assumed hostile — so it authenticates nothing. Anyone on the same segment can claim to be the gateway. This is how ARP cache poisoning turns that trust into a man-in-the-middle position, the tools that do it, what intercepting the traffic actually gets you, and the controls that shut it down.