ping of a Neighboring Device over Ethernet
Finally, as a brief review, routers use their IP ARP table to find the MAC address of another device that sits in the same LAN-based subnet. If the router has that other host’s IP and MAC address in its ARP table, the router can encapsulate IP packets inside an Ethernet frame, putting that device’s MAC address in the frame as the destination MAC address. If not, the router uses ARP messages to learn the neighboring device’s MAC address.
Example B-11 shows R2’s ARP table from Figure B-12. It shows only two entries, but you can identify the entry for R2’s own interface IP address (172.16.2.2) based on the – in the output. The – means that the entry will not time out. (The other entry, 0200.3333.3333, ...
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