Which device divides a single LAN into two segments but makes the two segments appear as one network to higher-layer protocols (i.e., forwards frames at Layer 2)?

Introduction / Context:
Network segmentation can improve performance while preserving a unified broadcast domain. Devices that forward based on MAC addresses at Layer 2 can split collision domains yet keep higher layers (IP, transport, application) unaware of the split.

Given Data / Assumptions:

• Goal: separate a LAN into segments while appearing as one network to higher layers.
• Forwarding decisions should be made using MAC addresses (Layer 2).
• No routing between IP subnets is desired.

Concept / Approach:

A bridge learns MAC addresses and forwards/filters frames between segments, maintaining a single IP subnet and broadcast domain. A modern Ethernet switch is essentially a multiport bridge and behaves the same way logically. Routers operate at Layer 3 and would create distinct networks. Gateways perform protocol translation at higher layers.

Step-by-Step Solution:

Verification / Alternative check:

Switches (multiport bridges) routinely segment traffic via MAC learning while keeping a single IP subnet, validating the choice of 'Bridge.'

Why Other Options Are Wrong:

Switch: Functionally similar but the classic term for a two-segment device is 'bridge'; the stem points to the textbook definition.

Gateway: Translates across protocols; not simple Layer-2 forwarding.

Router: Separates networks at Layer 3; not transparent to higher layers.

None of the above: Incorrect because a bridge fits exactly.

Common Pitfalls:

Assuming any interconnect is routing; here, the emphasis is on Layer-2 transparency.

Final Answer:

Bridge