In TCP/IP, what is ARP (Address Resolution Protocol) and what function does it perform on a local network segment?

Introduction:
Within a local Ethernet or Wi-Fi segment, devices deliver frames using link-layer addresses (for example, MAC addresses). IP, however, routes based on logical addresses. Bridging this gap requires a mapping mechanism so an IP next-hop can be contacted via its physical address on the shared medium.

Given Data / Assumptions:

• Hosts know an IP address they need to reach on the same subnet.
• They do not know the corresponding link-layer (hardware) address.
• Communication occurs over a broadcast-capable link such as Ethernet.

Concept / Approach:
Address Resolution Protocol (ARP) dynamically maps an IPv4 address to a hardware address (e.g., MAC). The host broadcasts an ARP request asking “Who has IP X.X.X.X? Tell Y.Y.Y.Y.” The owner replies with its hardware address. The requester caches this binding in an ARP table so future frames can be sent directly to the correct destination. ARP operates within the local subnet; routers perform ARP for their connected networks to forward IP packets at layer 2.

Step-by-Step Solution:
1) Host needs to send to an on-link IP → constructs an ARP request.2) LAN devices receive the broadcast; the target IP responds with its MAC.3) Sender updates ARP cache with IP↔MAC mapping.4) IP packet is then encapsulated in a frame addressed to that MAC.

Verification / Alternative check:
Use operating system tools (arp, ip neigh) to view cached mappings; packet captures show ARP requests/replies preceding unicast traffic.

Why Other Options Are Wrong:

• File transfer: FTP/HTTP handle that, not ARP.
• Monitoring: SNMP or ICMP echo are used instead.
• Error/control messages: ICMP performs that role.
• None of the above: invalid because option A is correct.

Common Pitfalls:
Confusing ARP (IPv4) with Neighbor Discovery in IPv6; ND provides similar functions using ICMPv6 messages.

Final Answer:
a TCP/IP protocol used to dynamically bind a high level IP Address to a low-level physical hardware address