router configuration problem

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I was solving GATE CSE problems from a book and this question was one of the objective questions in this book

Not sure of the circumstance of that question you saw, but in the networking world, "router configuration problem" is very ambiguous. Router configurations nowadays are advanced enough to extend through the whole OSI layers.

In most cases of troubleshooting, I suppose issues would fall under Layers 2 & 3.

Ash is right it depends on context the statement is mentioned.

As OSI model is composed of 7 Layer.
Layer 1 - Physical - cables, connectors and media { electrons(wired) , radio frequency(wireless), light (fibre) }
PDU - bits

Layer 2 - Data Link Layer - consist of two sub-layer
a) LLC (logical link control) which is closer to Network Layer
b) MAC (media access control) which is closer to Physical Layer and consist of MAC address.
Devices - network interface card (NIC) which is present in PC, Switches & Routers.
PDU - Frames

Layer 3 - Network Layer - logical address i.e. hierarchical addressing.
Device used is Router, PC or multi-layer switches where you can assign ip address.
PDU - Packet

Hence, data link layer is 1st possibility troubleshooting after receiving the signal from the wire (bits).

One example of Router configuration problem:
not assigning IP address to an router interface connected to LAN. If somebody on the LAN is trying to ping the router's ip address. Router is not reachable.