The GATE Grind

GATE 2019 CS – Question 39

Computer Networks · Data Link Layer: Error Detection, Medium Access Control, Flow Control · 2 marks · Multiple choice

Suppose in an IP-over-Ethernet network, a machine X wishes to find the MAC address of another machine Y in its subnet. Which one of the following techniques can be used for this?

  1. X sends an ARP request packet to the local gateway's IP address which then finds the MAC address of Y and sends to X
  2. X sends an ARP request packet to the local gateway's MAC address which then finds the MAC address of Y and sends to X
  3. X sends an ARP request packet with broadcast MAC address in its local subnet
  4. X sends an ARP request packet with broadcast IP address in its local subnet

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Show answer and explanation

Correct answer: (C) X sends an ARP request packet with broadcast MAC address in its local subnet

Explanation

ARP resolves an address within the local subnet by broadcasting a request at the Ethernet layer (destination MAC FF:FF:FF:FF:FF:FF), and the owner of the IP address replies. The gateway is not involved.