What describes the ARP cache (neighbor table)?

• A. Local mapping of IP to MAC stored by the OS; stale entries cause reachability issues.
• B. A global routing table used by core routers to forward packets.
• C. A database of DNS hostnames to IP addresses.
• D. The switch's MAC address table used for switching decisions.

Answer: (A)

The ARP cache is the host’s local map from IP addresses to MAC addresses on the local network, stored by the operating system to speed up communications. When a device needs to send a frame to another host on the same LAN, it first checks this cache to find the destination’s MAC address. If the mapping is present, the frame is sent directly using that MAC without waiting for another ARP request. If there’s no entry, the host issues an ARP request to discover the MAC, and the response is cached for future use. Entries eventually age out, and if they become stale—such as a device changing its MAC or moving to a different switch—the cached mapping can cause reachability issues until ARP resolves again. This is not a global routing table used by core routers, not a DNS database, and not the switch’s MAC address table.