OSI layer mapping for common devices and apps Fill in the layers: Routers operate at layer ___; LAN switches operate at layer ___; Ethernet hubs operate at layer ___; word processing applications operate at layer ___.

Introduction / Context:
The OSI reference model provides a layered way to understand networking functions. Correctly mapping common devices to their primary layers helps in troubleshooting and design. While devices can process information at multiple layers, each has a primary role associated with a specific OSI layer.

Given Data / Assumptions:

• Devices: router, LAN switch, Ethernet hub, and an end-user word processing application.
• We are mapping each to its principal OSI layer of operation.

Concept / Approach:

Routers make forwarding decisions using Layer 3 (Network) information such as IP addresses. LAN switches forward based on Layer 2 (Data Link) MAC addresses and maintain MAC tables per VLAN. Hubs simply repeat bits at Layer 1 (Physical), creating a single shared collision domain. Applications like word processors operate at Layer 7 (Application), using network services provided by lower layers.

Step-by-Step Solution:

Verification / Alternative check:

Use CLI outputs: a switch show mac address-table confirms L2 functions; a router show ip route highlights L3. A hub lacks such intelligence and merely regenerates signals.

Why Other Options Are Wrong:

• Options placing switches at Layer 3 conflate multilayer switching with basic LAN switching.
• “None” for applications ignores the Application layer role.
• Any mapping of hubs beyond Layer 1 is incorrect; hubs do no frame or packet processing.

Common Pitfalls:

• Confusing multilayer (L3) switches with pure L2 operation; here the question specifies “LAN switches,” implying L2.
• Assuming apps operate at multiple layers; while they rely on lower layers, their functional layer is L7.

Final Answer:

3, 2, 1, 7