GATE CS 2021 Set 1 Q8 — Concept of Layering: OSI and TCP/IP Protocol Stacks

To determine the correctness of the statements, let us analyze how the Address Resolution Protocol (ARP) operates:

• Statement $S_1$ (ARP Reply): When the target host receives an ARP request, it learns the sender's MAC address from the request packet. Since the target now knows exactly who requested the information, it sends the ARP reply directly to the requester as a unicast frame.
  Therefore, the destination MAC address of an ARP reply is a unicast address, not a broadcast address.
  $S_1$ is False.


• Statement $S_2$ (ARP Request): When a host needs to find the MAC address corresponding to a specific IP address, it does not yet know which physical device owns that IP. Thus, it must query all hosts on the local network segment by sending an ARP request as a broadcast frame.
  The destination MAC address in the Ethernet header is set to the broadcast address (FF:FF:FF:FF:FF:FF).
  $S_2$ is True.

Since $S_1$ is false and $S_2$ is true, the correct choice is C.