Which device operates across both the Data Link (Layer 2) and Network (Layer 3) layers, combining bridging with routing capabilities?

Introduction / Context:
Network devices are categorized by the highest OSI layer at which they make forwarding decisions. Some hybrid devices can bridge some traffic and route other traffic, providing flexible segmentation and interconnection in complex LAN/WAN designs.

Given Data / Assumptions:

• We need a device that can forward on MAC addresses (Layer 2) and also on IP/network addresses (Layer 3).
• Bridging is used within broadcast domains; routing moves traffic between subnets.

Concept / Approach:
A brouter (bridge + router) can act as a bridge for non-routable or certain protocol frames while routing routable protocols based on Layer-3 headers. This dual capability allows gradual migration and nuanced control over traffic flows in mixed environments.

Step-by-Step Solution:

Verification / Alternative check:
Legacy multi-protocol networks used brouters to bridge non-IP traffic (e.g., AppleTalk/NetBEUI) while routing IP, reducing broadcast domains without breaking non-routable services.

Why Other Options Are Wrong:

• NIC: operates at Layers 1–2 for a host; not a forwarding device.
• Bridge: Layer 2 only.
• Router: Layer 3 only.
• None: incorrect because a brouter exists for this purpose.

Common Pitfalls:
Assuming switches (Layer 2) are the same as routers; overlooking hybrid devices in mixed-protocol environments; forgetting that modern multilayer switches integrate L2/L3 but the classic term for a combined function is “brouter.”

Final Answer:
Brouter