While troubleshooting Internet access problem reported by a user, a computer technician finds that the default gateway setting is wrong. Which layer of OSI model is associated with the cause of the problem experienced by the user?
Layer 2
Layer 5
Layer 3
Layer 4
ANSWER
The cause of the problem is at Layer 3 (the network layer), option (c).
Official answer: CSource: ISRO's final answer key of 15 May 2026
The default gateway is the router address to which a host sends a packet when the destination IP address lies outside its own subnet.
Choosing a next hop from the destination IP address and forwarding packets between networks is routing. Routing and logical (IP) addressing belong to the network layer, Layer 3.
A wrong default gateway breaks only traffic that must leave the local subnet. Communication inside the subnet keeps working. The gateway is part of the host's IP configuration, which is a Layer 3 setting.
Layer 2 (data link) uses MAC addresses and switching inside one network. The gateway setting is not part of it.
Layer 4 (transport) handles ports, segmentation and reliability between end processes. It does not choose routes.
Layer 5 (session) manages dialogues between applications and has nothing to do with the gateway address.
Hence the fault lies at Layer 3, the network layer.
KEY IDEA
The default gateway is an IP-level routing setting: it tells a host where to send packets for destinations outside its subnet. IP addressing and routing are Layer 3 functions.
WATCH OUT FOR
Choosing Layer 2 because the gateway is a physical device on the local link, or Layer 4 because the symptom is an application not working. Hosts reach the gateway at Layer 2 using its MAC address, but the setting that is wrong is the gateway's IP address, which belongs to Layer 3.
From the ISRO CS 2025 paper. Every question of this paper · The full paper (PDF, ISRO) · All 2 ISRO Layering & switching questions, with notes
