ARP (Address Resolution Protocol)
Address Resolution Protocol (ARP), defined in RFC 826, maps a device's IPv4 address to its link-layer (MAC) address on a local network, since IP packets carry an IP address but the local network hardware needs a MAC address to actually deliver a frame. A device that needs to reach another IP address on the same subnet broadcasts an ARP request asking "who has this address," and the device that holds it replies directly with its MAC address; the asking device then caches that mapping in an ARP table for a short period to avoid repeating the broadcast for every packet. ARP has no built-in authentication, so any device on the same broadcast domain can reply to a request it was never asked, which is the basis of ARP spoofing. IPv6 does not use ARP at all, relying on Neighbor Discovery Protocol instead.
By AdminKit team, Netbase JSC · Updated