Which network device is used to separate broadcast domains?

A router operates at OSI Layer 3 and by default does not forward Layer 2 broadcast frames, meaning each router interface defines a separate broadcast domain. This is a fundamental distinction from Layer 2 devices, which propagate broadcasts within a network segment. Each subnet connected to a router interface is its own isolated broadcast domain.

A repeater operates at Layer 1 and simply regenerates electrical signals, forwarding all traffic including broadcasts and thereby expanding, not separating, broadcast domains.

A switch operates at Layer 2 and separates collision domains but forwards broadcasts to all ports in the same VLAN, so it does not separate broadcast domains.

A bridge also operates at Layer 2 and separates collision domains but still forwards broadcast frames across its ports, so it does not create separate broadcast domains.