the.com/arp
the internet's honor system for turning ip addresses into mac addresses, and everyone just lies.
means address resolution protocol maps a known ip address to the physical hardware address of the device that owns it on a local network.
from defined in 1982 by rfc 826, back when networks were small enough that trusting every device to answer honestly seemed like a reasonable design choice.
no authenticationany device can claim any ip address
cache poisoningbasis for arp spoofing man-in-the-middle attacks
broadcast basedasks the entire network who owns an ip
ipv6 replacementndp does this job instead, still imperfectly
for instance
arp spoofing attacks — classic technique behind ettercap and cain and abel toolkits
arpwatch — 1990s tool that logs suspicious ip-to-mac changes
gratuitous arp — used by routers for failover in vrrp and hsrp