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Networking Fundamentals · Foundational

ARP Cache

The table a host or router keeps of recently resolved IPv4-to-MAC mappings.

Definition

Entries age out after a timeout (minutes on hosts, four hours by default on Cisco routers) and can be dynamic or static. Viewing the cache confirms whether a host has resolved its gateway's MAC, and clearing it can resolve stale entries after hardware changes.

Example

arp -d * on Windows clears the ARP cache.

Exam tip

An incomplete ARP entry for the gateway points to a Layer 1 or 2 problem between host and router.

Related terms