This counter tracks packets dropped because the ARP table lacked an entry for the packet's next hop. Unlike the no-route counter, which reflects a routing-table gap, this counter reflects a Layer-2 resolution failure for a next hop the router does have a route to -- commonly seen when a downstream Ethernet device is powered off, disconnected, or has changed its MAC address without the router's ARP cache updating. If a downstream server is rebooted with a new NIC and this counter starts climbing for packets destined to its known IP, that's a sign the router's ARP cache needs to refresh before forwarding can resume.