Which of the following devices works at the network layer of the ISO-OSI…
2023
Which of the following devices works at the network layer of the ISO-OSI reference model?
Answer: B. Router — Concept: in the ISO-OSI model a device belongs to the highest layer whose information it actually interprets. A physical-layer (Layer 1) device handles only…
- A.
Hub
- B.
Router
- C.
Amplifier
- D.
Repeater
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Show answer & explanation
Correct answer: B
Concept: in the ISO-OSI model a device belongs to the highest layer whose information it actually interprets. A physical-layer (Layer 1) device handles only the raw signal or bit stream and reads no address at all; a data-link-layer (Layer 2) device interprets MAC frame headers inside one network; a network-layer (Layer 3) device interprets logical (IP) addresses and forwards packets between separate networks along a path it chooses.
Application: among the devices listed, the router is the one that opens the network-layer header of a packet, reads the destination IP address, looks it up in its routing table, decrements the TTL and forwards the packet out of the interface leading toward the destination network. Choosing a path between different networks on the basis of logical addresses is precisely the network layer's responsibility, so the router works at the network layer.
Contrast with the other devices listed:
Device | What it interprets | OSI layer |
|---|---|---|
Hub | Nothing but the incoming electrical signal, which it copies out of all its other ports | Physical (Layer 1) |
Repeater | Nothing but the bit stream, whose shape it regenerates and whose bits it retimes | Physical (Layer 1) |
Amplifier | Nothing but the analog waveform, whose amplitude (and noise) it raises | Physical (Layer 1) |
Cross-check: identify a device's layer by asking what information it reads.
What the device reads | OSI layer | Example devices |
|---|---|---|
Only the signal or the raw bit stream | Physical (Layer 1) | Hub, repeater, amplifier |
MAC (physical) addresses in a frame | Data link (Layer 2) | Switch, bridge |
IP (logical) addresses in a packet | Network (Layer 3) | Router |
Only the router in this list reads IP addresses and forwards packets between separate networks, which confirms that the answer is Router.