GATE CSE 2024 Set 2 · Q23
Time
Node X has a TCP connection open to node Y. The packets from X to Y go through an intermediate IP router R. Ethernet switch S is the first switch on the network path between X and R. Consider a packet sent from X to Y over this connection.
Select all that applyOne or more correct
Solution
Official answer: B) The destination IP address is the IP address of Y
Principles of LayeringWhen node X sends a packet to node Y located in a different subnet through router R:
Destination IP Address:
The IP header carries the end-to-end network layer addressing. Therefore, the destination IP address remains the IP address of the final destination node, Y.
Hence, statement (B) is correct and statement (A) is incorrect.
Destination MAC Address:
The data-link layer frame addresses the next-hop network-layer device. Here, the first router on the path to Y is R. Node X determines the MAC address of R's incoming interface (using ARP).
A standard Ethernet switch S operates at Layer 2 (data link layer) and acts transparently; frames are not addressed to the switch's MAC address for normal forwarding.
Therefore, the destination MAC address of the frame when leaving X is the MAC address of router R, not S and not Y.
Hence, statements (C) and (D) are incorrect.
Try the question first, then check your work.
Examiner trap
Remember that IP addresses specify the end-to-end destination, whereas MAC addresses specify the next-hop router on the local link. Layer 2 switches are transparent forwarders.
This Principles of Layering previous year question is Q23 of the GATE CSE 2024 Set 2 paper. Find more GATE CSE PYQs on Principles of Layering in Computer Networks, or browse all GATE CSE PYQs.
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Principles of Layering has 12 GATE CSE PYQs across 10 papers from 2011 to 2025. This is the only 1-mark MSQ among them, and it is the only one in GATE CSE 2024 Set 2.
How GATE tests Principles of LayeringIndependent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.