Local networks
ARP resolves IPv4 neighbors
Use ARP to map a local IPv4 next-hop address to the Ethernet address needed for a frame.
8 minute lesson
Before sending an IPv4 packet over Ethernet, a host needs the MAC address of the next hop. The Address Resolution Protocol, or ARP, maps a local IPv4 address to an Ethernet address.
The sender broadcasts a request asking which interface owns an IPv4 address. The owner replies with its MAC address, and the sender stores the answer temporarily in its neighbor cache.
For a destination on the same subnet, the next hop is the destination itself. For a remote destination, the next hop is usually the default router. ARP resolves the router’s local address, not the remote server’s address.
A stale or missing neighbor entry can stop communication before the first packet leaves the LAN. Inspecting the neighbor cache is therefore a useful local diagnostic.
Lesson completed