Which function is performed by ARP protocol?

The Address Resolution Protocol (ARP) is a fundamental Layer 2 protocol used to map a known Layer 3 address (specifically an IPv4 address) to its corresponding Layer 2 physical address (such as a MAC address). When a device needs to send a packet to another device on the same local network, it uses an ARP request, broadcast to the network, to ask which device is using a specific IP address. The target device responds with an ARP reply containing its MAC address, allowing the source to build the complete Layer 2 frame for transmission.

B. discover directly connected neighbors

While ARP helps find the MAC address of a known IP neighbor, protocols like Link Layer Discovery Protocol (LLDP) are specifically designed for neighbor discovery, exchanging device capabilities and identity.

C. build and maintain switch MAC tables

A switch builds its MAC address table by inspecting the source MAC address of all incoming frames on its ports, a process called MAC learning. This is a function of the switch, not the ARP protocol itself.

D. resolve host name

Resolving a hostname (e.g., www.ruckus.com) to an IP address is the function of the Domain Name System (DNS) protocol, which operates at the Application Layer.

1. RUCKUS FastIron IP Routing Configuration Guide, 08.0.90

Section: Chapter 2, "Configuring IP," page 33.

Quote: "Address Resolution Protocol (ARP) is a protocol for mapping an Internet Protocol address (IP address) to a physical machine address (MAC address) that is recognized in the local network." This directly confirms that ARP's function is to resolve IP addresses to MAC addresses.

2. Internet Engineering Task Force (IETF) RFC 826: An Ethernet Address Resolution Protocol

Section: Abstract.

Quote: "A protocol for the conversion of 32-bit internet addresses to 48-bit Ethernet addresses is presented." This is the foundational document defining the primary purpose of ARP.

3. MIT OpenCourseWare, 6.02 Introduction to EECS II: Digital Communication Systems, Fall 2012

Section: Lecture 20 Notes, "Protocols & Layering."

Content: The lecture notes explicitly describe ARP's role in the networking stack: "ARP (Address Resolution Protocol) is used by a node to determine the MAC address of a node whose IP address is known." It also separately describes how switches learn MAC addresses by observing source addresses on frames, clearly distinguishing this function from ARP.