This read-write integer sets, in seconds, how long an inactive ARP entry is kept before the device removes it from its ARP cache, defaulting to 4 hours. An admin lowers this value in environments with frequent IP reassignment, such as DHCP with short leases, to avoid the router holding stale MAC-to-IP mappings. For example, shortening this timeout on a VLAN with high host churn helps the router purge outdated ARP entries faster and avoid delivering traffic to the wrong MAC address.