If ARP is set to reply-only, what is needed for the router to communicate with any other host on the network?

• A. Static ARP entry
• B. Dynamic ARP cache
• C. Proxy ARP
• D. DNS entry

Answer: (A)

In ARP, the device learns which MAC address goes with which IP on the local network. When ARP is set to reply-only, the router will not actively send ARP requests to learn new MAC addresses; it can only answer ARP requests for addresses it already knows. To communicate with another host, the router must have a MAC address mapping for that destination IP already stored. Since it won’t learn new mappings automatically, you must configure a static ARP entry that binds the destination IP to its MAC address. DNS entries don’t affect ARP, and dynamic ARP cache wouldn’t help because the router won’t issue ARP requests to populate it. Proxy ARP could alter reachability in some designs, but the direct requirement to ensure communication under reply-only ARP is a static ARP entry.