What device is used to interconnect unlike LANs?

The device that interconnects unlike LANs is a gateway. A gateway serves as a "gate" between two networks and enables communication between different protocols. This means that if one local area network (LAN) is using a different protocol or addressing scheme than another, the gateway can translate the necessary information so that the communication can take place seamlessly.

Gateways can operate at various layers of the OSI model, making them versatile in handling different types of data. For example, they can manage not just IP traffic but can also provide functionalities such as protocol conversion, allowing for data transfer between disparate networks.

In contrast, routers typically connect similar networks and operate primarily at the network layer (Layer 3). Bridges connect two comparable networks at the data link layer (Layer 2) to form a single network, and repeaters amplify signals to extend the reach of a network but do not perform protocol conversion. Therefore, while routers, bridges, and repeaters serve important roles in networking, a gateway specifically addresses the need to connect different types of networks and protocols.