ARPneighbor

ARPneighbor is a term used in computer networking to describe the relationship established by the Address Resolution Protocol (ARP) between an IPv4 address and a corresponding link-layer (MAC) address for devices on the same local network segment. An ARPneighbor entry represents a cached mapping that a host maintains in its ARP table to enable direct communication with a neighbor without repeated broadcasts.

The ARP process creates ARPneighbor entries when a host needs to send data to an IPv4 address not yet associated with a MAC address. The sender broadcasts an ARP request asking “Who has this IP? Please send your MAC.” The device with the matching IP replies with an ARP reply containing its MAC address, and the sender stores the IP-to-MAC mapping as an ARPneighbor. Entries typically have an aging timer and may be refreshed by subsequent traffic or by gratuitous ARP messages, which can also update existing mappings or detect IP conflicts. Proxy ARP can allow neighboring devices on different networks to be reachable through intermediate routers.

ARPneighbor is confined to the same broadcast domain, as ARP operates at Layer 2. In IPv6 networks, the equivalent functionality is provided by the Neighbor Discovery Protocol rather than ARP. Security considerations include ARP spoofing or poisoning, where an attacker misleads devices about MAC addresses. Mitigations include static ARP entries, dynamic ARP inspection, DHCP snooping, port security, and network segmentation through VLANs. Proper management of ARP neighbors helps reduce misdirected traffic and improves network reliability.