Which network device breaks networks into separate broadcast domains?

A router is a network device that operates at Layer 3 (the Network Layer) of the OSI model. Its primary function is to forward data packets between different computer networks. By design, routers do not forward Layer 2 broadcast frames from one network interface to another. Each interface on a router represents the boundary of a broadcast domain. Therefore, when a device sends a broadcast message, it is contained within its local network segment and is not passed on by the router to other connected networks, effectively breaking the network into separate broadcast domains. This segmentation is crucial for managing network traffic, improving performance, and enhancing security.

A. Hub: A hub is a Layer 1 device that regenerates and repeats all incoming electrical signals to all of its ports, creating a single, large broadcast domain.
B. Layer 2 switch: By default, a Layer 2 switch forwards broadcast frames to all ports within the same network segment or VLAN, thus forming a single broadcast domain.
D. Wireless access point: A wireless access point typically functions as a Layer 2 bridge, connecting wireless clients to a wired network and extending the existing broadcast domain. ---

1. Palo Alto Networks. (2021). PCCET Palo Alto Networks Certified Cybersecurity Entry-level Technician Study Guide. "A router is a Layer 3 device that forwards data between computer networks... Routers break up broadcast domains, which means that a broadcast sent by a host on one network will not be forwarded by the router to another network." (Chapter 2: The Connected Globe, Section: Network Devices, p. 31).

2. Kurose, J. F., & Ross, K. W. (2021). Computer Networking: A Top-Down Approach (8th ed.). Pearson. In the discussion of the link layer and network layer, the text clarifies the roles of switches and routers. Switches (link-layer devices) forward broadcast frames, while routers (network-layer devices) do not, thereby isolating broadcast domains. (Chapter 4: The Network Layer: Data Plane, Section 4.4 & Chapter 6: The Link Layer and LANs, Section 6.3).

3. Stanford University. (2023). CS144: Introduction to Computer Networking, Lecture 5: Routing. The course materials explain that a fundamental purpose of routers is to interconnect different networks (e.g., different Ethernet LANs), and in doing so, they do not forward link-layer broadcasts between these networks, thus creating separate broadcast domains.