What is the primary function of the ARP in an IPv4 local network?
2024
What is the primary function of the ARP in an IPv4 local network?
- A.
To assign IP addresses dynamically
- B.
To resolve domain names into IP addresses
- C.
To determine the MAC address corresponding to an IP address
- D.
To encrypt network communication
- E.
To forward packets between different networks
Attempted by 19 students.
Show answer & explanation
Correct answer: C
The Address Resolution Protocol (ARP) is used in an IPv4 local network to find the MAC (hardware/physical) address that corresponds to a known IPv4 address. Hosts identify each other logically by IP address, but to actually deliver a frame on the same LAN segment they need the destination's Layer-2 MAC address — ARP bridges this gap.
When a host wants to send data to an IP address on the same network and does not have the matching MAC address cached, it broadcasts an ARP request ("Who has IP X? Tell me your MAC."). The host owning that IP replies with a unicast ARP reply carrying its MAC address, which the sender stores in its ARP cache for future use.
Therefore, the primary function of ARP is to determine the MAC address corresponding to a given IP address — i.e., to map an IP (network-layer) address to a MAC (link-layer) address. This makes option (3) correct.
Why the others are wrong: assigning IP addresses dynamically is done by DHCP; resolving domain names to IP addresses is done by DNS; encrypting communication is the job of protocols such as IPsec/TLS; and forwarding packets between different networks is performed by routers (the IP routing/forwarding function).