ARP cache
also: ARP table, neighbor cache, MAC cache
A table that maps IP addresses to MAC addresses on a local network, cached by the operating system to speed up network communication.
ARP (Address Resolution Protocol) cache stores recent IP-to-MAC address mappings discovered during network communication. Instead of sending an ARP request every time a packet needs to be sent to an IP address on the local network, the system checks this cache first, dramatically improving performance.
Each entry in the ARP cache typically includes the IP address, corresponding MAC (hardware) address, and a timestamp. Entries expire after a period of inactivity (usually 5–15 minutes) to handle cases where a device changes its MAC address or leaves the network.
You can view the ARP cache on Linux using arp or ip neigh show. For example, ip neigh show displays entries like 192.168.1.100 dev eth0 lladdr aa:bb:cc:dd:ee:ff REACHABLE, indicating that IP 192.168.1.100 is reachable on interface eth0 with that MAC address.