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Networking Fundamentals · Foundational

Address Resolution Protocol (ARP)

The protocol (RFC 826) that resolves a known IPv4 address to the corresponding MAC address on the local network.

Definition

A host broadcasts an ARP request asking who owns an IP address, and the owner replies with its MAC by unicast. Results are stored in the ARP cache. For remote destinations, the host ARPs for its default gateway rather than the final destination. IPv6 replaces ARP with NDP.

Example

arp -a on Windows lists the IP-to-MAC mappings the host has learned.

Exam tip

A host ARPs for the gateway, not the remote host, when the destination is on another subnet.

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