The device which connects dissimilar LANs of different topologies using…

CONCEPT: Internetworking devices sit at different layers and handle different degrees of dissimilarity between the networks they connect. A gateway is the device that connects networks differing in topology AND in their entire protocol stack — it performs full protocol translation so that data formatted for one network becomes usable on the other.

APPLICATION: The stem describes a device connecting dissimilar LANs of different topologies that also use different sets of communication protocols. This is exactly the gateway's defining role — translating across protocol families between fundamentally different network architectures, not merely extending or switching within one network.

CROSS-CHECK — how the other devices differ:

• Router: forwards packets between networks at the network layer, but within a common network-layer protocol suite (for example, IP-to-IP); it does not translate between different protocol families.

• Bridge: works at the data-link layer and joins two segments that use the SAME data-link protocol, extending one logical network — it cannot interconnect networks with differing protocol stacks.

• Switch: works at the data-link layer inside a single LAN, forwarding frames between devices on that same network by MAC address — it does not interconnect separate networks running different protocols.

Since only a gateway performs full protocol-stack translation between dissimilar networks, that is the correct device.