In classical TCP/IP networks, which protocol does a diskless client use to discover its Internet Protocol (IP) address from a local server when it only knows its hardware (MAC) address?

Introduction / Context:
Before DHCP became ubiquitous, early workstations often booted over the network without any preconfigured IP address. They needed a protocol that could map a known MAC address to an appropriate IP address, enabling the boot process to continue and higher-layer configurations to load.

Given Data / Assumptions:

• The client has only its link-layer identity (MAC address).
• Objective: obtain an IP address from a server on the same LAN.
• Context: legacy TCP/IP (RARP/BOOTP era) rather than modern DHCP-only environments.

Concept / Approach:
Reverse Address Resolution Protocol (RARP) performs the inverse of ARP: it queries a RARP server with a MAC address and receives the corresponding IP address. BOOTP and DHCP later generalized and extended this function, but the direct historical answer to “MAC → IP” is RARP.

Step-by-Step Solution:
Identify the mapping direction required: MAC → IP.Match to protocol designed for this purpose: RARP.Exclude routing (RIP), remote desktop (RDP), and packet-switched link standards (X.25) as unrelated.

Verification / Alternative check:
In many textbooks, the boot sequence for diskless clients begins with a RARP request, followed by TFTP image retrieval; modern stacks replace RARP with DHCP/BOOTP but the principle remains similar.

Why Other Options Are Wrong:
RDP: Remote Desktop Protocol; unrelated to address discovery.

RIP: Routing Information Protocol; distributes routes, not host addresses.

X.25: Packet-switched network suite; not an IP address assignment mechanism.

None of the above: Incorrect because RARP is correct.

Common Pitfalls:
Confusing ARP (IP → MAC) with RARP (MAC → IP). The word “Reverse” is the key memory cue.

Final Answer:
RARP