Which technology does NOT isolate broadcasts?

The correct answer is based on the understanding of how different network devices operate regarding broadcast traffic. A hub, as a basic networking device, operates at the physical layer of the OSI model. It is designed to receive data packets and broadcast them to all connected devices within the same local area network segment. This means that any data sent to the hub is forwarded to all its ports, thereby not isolating broadcasts in any way.

In contrast, a router, a device that operates at the network layer, routes traffic between different networks and does not forward broadcast packets. It essentially separates network segments, handling only the traffic meant for specific addresses. VLAN (Virtual Local Area Network) allows the segmentation of a physical network into logical groups, effectively isolating broadcast domains within the same hardware. Firewalls, while primarily focused on security, also perform packet filtering and can separate networks, further preventing broadcast packets from being transmitted across different segments.

Given these functions, the hub stands out as the device that does not offer any mechanism for isolating broadcast traffic, confirming it as the correct answer.