What is ARP and what are its two basic functions?
ARP lets an IPv4 device find the MAC address of a local device when it already knows that device's IPv4 address; its two functions are resolving IPv4→MAC and maintaining the ARP table of those mappings.
ARP (Address Resolution Protocol): A device uses ARP to determine the destination MAC address of a local device when it knows its IPv4 address.
Two basic functions of ARP:
| Function | Description |
|---|---|
| Resolving IPv4 addresses to MAC addresses | Discovers the MAC address associated with an IPv4 address |
| Maintaining an ARP table | Caches IPv4-to-MAC address mappings for faster subsequent lookups |
Context: ARP is essential because Ethernet frames require MAC addresses for local delivery, but applications and upper layers work with IP addresses.
Go deeper:
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ARP Explained - Address Resolution Protocol — animated overview of what ARP does and how it resolves an IPv4 address to a MAC. -
RFC 826 — An Ethernet Address Resolution Protocol — Plummer's original 1982 spec defining ARP and the table it builds to translate protocol addresses to 48-bit Ethernet addresses. -
Address Resolution Protocol — Wikipedia covers both ARP functions: resolving IPv4 to MAC and caching the mappings.