In computer networking, devices operate at different layers of the OSI reference model. Among the following options, which device is primarily associated with the network layer, where it forwards packets based on logical IP addresses?

Introduction / Context:
This question tests knowledge of how common network devices map to the layers of the OSI model. Understanding which device operates at which layer helps you design, troubleshoot, and secure networks. The network layer is responsible for logical addressing and routing of packets between different networks, and one particular device is central at this layer. Recognizing that routers perform network layer functions is a basic part of networking literacy.

Given Data / Assumptions:

• The question asks which device is used in the network layer.
• The options include repeaters, routers, application gateways, and switches.
• We assume the standard OSI model where the physical layer is at the bottom, followed by data link, network, transport, session, presentation, and application.
• We also assume that IP based packet forwarding is the key responsibility at the network layer.

Concept / Approach:
The network layer, often described in terms of IP, handles logical addressing and routing. A router is a device that examines packet headers containing IP addresses and decides where to forward the packets, possibly across different networks. This is the core function of the network layer. Repeaters operate at the physical layer; they simply regenerate and amplify signals to extend the range of a network segment. Switches mainly operate at the data link layer, forwarding frames based on MAC addresses, although some advanced devices combine features from multiple layers. Application gateways work at higher layers, translating or proxying application protocols such as HTTP or FTP. Therefore, the device most clearly associated with the network layer is the router.

Step-by-Step Solution:
Step 1: Recall that the network layer deals with logical addressing and routing, typically using IP addresses.Step 2: Identify the device that reads IP headers and makes forwarding decisions based on destination networks.Step 3: Recognize that routers are defined by this function and are installed at the boundaries between networks.Step 4: Note that repeaters and switches operate at the physical and data link layers, not the network layer.Step 5: Conclude that the router is the device that belongs to the network layer in the OSI model.

Verification / Alternative check:
Networking textbooks and certification materials consistently classify routers as network layer devices. Diagrams of network topologies show routers connecting different IP subnets and sometimes linking local area networks to the wider internet. Device configuration interfaces for routers focus on IP addressing, routing tables, and protocols such as OSPF or BGP, all of which belong to the network layer. Meanwhile, repeaters and switches are described in terms of physical media and MAC addresses, confirming that they operate at lower layers. This evidence supports the conclusion that routers are the primary network layer devices.

Why Other Options Are Wrong:
Option A is incorrect because repeaters simply regenerate electrical or optical signals and are therefore classified at the physical layer. Option C is incorrect because application gateways operate at the application layer, dealing with specific application protocols rather than generic packet forwarding. Option D is incorrect because switches are primarily data link layer devices that use MAC addresses to forward frames within a local network. Only option B, router, which forwards packets between networks based on IP addresses, correctly identifies a network layer device.

Common Pitfalls:
One common pitfall is to assume that all network devices operate at the same layer simply because they connect cables or computers. Another mistake is confusing layer 2 switches with layer 3 switches, which combine switching and routing functions. For exam style questions, it is usually safest to associate repeaters with the physical layer, switches with the data link layer, and routers with the network layer, unless the question explicitly mentions advanced multi layer devices. Keeping this simple mapping in mind helps avoid confusion and clarifies the roles of each device in a network.

Final Answer:
The correct answer is Router, which forwards packets between networks based on IP addresses.