Certified - CompTIA Network +

In Episode Eighty-Nine of the Network Plus PrepCast, we take a look at hubs and bridges, two network devices that once played a central role in small to medium-sized environments. These legacy devices have largely been replaced by more advanced technologies, but their functionality, behaviors, and limitations are still tested on the certification exam. Understanding them not only provides historical context but also deepens your grasp of how modern networking has evolved. In some roles, especially in environments that still maintain legacy systems, you might even encounter them. The certification expects you to recognize their characteristics, their operational layers, and their relevance to network design concepts.
Even though you are unlikely to work with hubs or bridges in a modern enterprise network, they continue to show up in exam questions. You may see comparative questions that test your ability to distinguish between older and newer devices. You might also need to explain how switching solved the problems introduced by earlier devices. By knowing how hubs and bridges work, and how they differ from switches and routers, you’ll have the background necessary to answer scenario-based questions effectively. This knowledge also anchors your understanding of concepts like collision domains, broadcast domains, and Layer 1 and Layer 2 operations.
A hub is one of the simplest network devices ever used. It functions by receiving incoming electrical signals on one port and replicating that signal to all other ports. A hub operates at Layer One of the O S I model, meaning it does not interpret the contents of frames or packets. It simply repeats bits at the physical level. This lack of logic means the hub cannot identify where the data should go. It treats all incoming signals the same, broadcasting them without discrimination across the network.
Because of this simplistic behavior, hubs come with a variety of limitations. Since they do not segment the network or manage traffic, all connected devices share the same bandwidth. When multiple devices try to communicate at the same time, data collisions occur. These collisions force retransmissions and slow down the entire network. Hubs lack any intelligence, meaning they do not perform filtering, learning, or any type of traffic optimization. They are essentially just repeaters with multiple ports.
When using a hub, all connected devices exist within the same collision domain. This means that any device transmitting can interfere with any other device on that hub. There is no isolation between segments, and there is no mechanism to manage traffic flow. As a result, network performance suffers when more devices are added. The more active devices on a hub, the higher the collision rate, which leads to reduced throughput and increased latency for all users.
Bridges were introduced to address the problems created by hubs. While hubs operated purely at Layer One, bridges worked at Layer Two of the O S I model. A bridge was designed to separate a network into multiple collision domains by examining the source and destination MAC addresses of Ethernet frames. Using this information, it could forward or filter traffic between network segments, which helped improve efficiency and reduce collisions.
The way a bridge works involves learning the location of devices by observing the MAC addresses in incoming frames. It builds a table of MAC addresses and the ports they are associated with. When a frame arrives, the bridge looks up the destination MAC in its table. If it knows the correct port, it forwards the frame only to that port. If not, it floods the frame to all segments except the one it came from. This process introduces basic intelligence to the network and allows for more efficient traffic delivery.
A typical bridge includes two interfaces, each connected to a separate network segment. When a frame comes in on one side, the bridge examines both the source and destination MAC addresses. If the destination is on the same side, the bridge filters the frame and does not forward it. If the destination is on the opposite segment, it forwards the frame accordingly. This behavior reduces unnecessary traffic between segments and increases overall network performance.
Although both bridges and switches operate at Layer Two, they differ in scale and complexity. Bridges are suitable for small environments with limited devices. They typically support two or three interfaces. Switches, on the other hand, are more scalable and capable of managing dozens or even hundreds of interfaces. A switch can be thought of as a multiport bridge with advanced capabilities, including support for V L A Ns, higher processing speed, and more extensive learning algorithms.
Bridges were commonly used before switches became affordable and widespread. In the early days of networking, bridges helped small offices divide networks into segments without the need for expensive or complex equipment. However, as networks grew in size and complexity, the limited scalability of bridges became a problem. This limitation paved the way for the adoption of switches as the standard Layer Two device.
The eventual replacement of hubs and bridges was driven by several factors. First, there was an increasing need for scalability, as networks grew beyond just a few segments. Second, traffic volumes increased, requiring more efficient ways to manage frames and reduce collisions. Finally, newer devices like switches offered features that made them vastly superior, including MAC address learning, segmentation, and support for modern technologies like V L A Ns. These advancements made legacy devices obsolete in most environments.
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In Episode Eighty-Nine of the Network Plus PrepCast, we focus on legacy networking devices that played key roles in early infrastructure designs—hubs and bridges. These devices helped shape the foundational concepts of network communication, and while they have been largely replaced by more efficient technologies, their understanding remains relevant. For the certification exam, you are expected to grasp how these devices operated, the problems they introduced, and how modern alternatives addressed those issues. Hubs and bridges laid the groundwork for current networking standards, and their study reveals important concepts like traffic forwarding, collision domains, and network segmentation. Even though you might not encounter them in modern enterprise networks, their relevance on the exam is clear and their legacy continues in the behaviors of more advanced devices.
The exam continues to reference hubs and bridges in a number of comparative or foundational questions. These devices often appear in contrast with modern alternatives like switches and routers. Their limited capabilities help define the improvements made by newer devices, which is why legacy equipment still finds a place in exam content. Understanding hubs and bridges helps you comprehend how networking evolved from shared broadcast models to efficient, segmented topologies. Even when the devices themselves are no longer in use, their roles and functions are essential reference points for interpreting scenarios, especially those related to collisions, broadcast behavior, and segment isolation.
A hub is a basic physical-layer device that connects multiple computers in a network by simply repeating electrical signals. When data is sent to a hub, it takes the signal and broadcasts it to all other connected ports regardless of destination. This makes the hub a purely Layer One device within the O S I model. It does not inspect the data packet, nor does it make any forwarding decisions based on destination information. The hub essentially acts as a multi-port repeater, creating a single large network segment without any internal traffic control or decision-making logic.
Because hubs lack any intelligence, they introduce several inefficiencies. One of the most pressing limitations is that all devices connected to a hub share the same total bandwidth. If multiple users attempt to transmit data simultaneously, the hub cannot prioritize or manage those transmissions. This often leads to data collisions, where overlapping transmissions corrupt each other. When collisions occur, the devices involved must detect the issue and retransmit, which adds delay and increases network congestion. Over time, especially as more devices are added, the network becomes increasingly inefficient under a hub-based design.
One of the defining features of a hub-based network is the presence of a single collision domain. In such an environment, any device that transmits data can interfere with any other device's transmission. There is no separation or segmentation of traffic flows. All devices exist in the same space in terms of traffic, which severely limits the performance and scalability of the network. This design can create an overwhelming number of collisions, making it impractical for anything more than the smallest and simplest networks.
Bridges were introduced to mitigate some of the traffic problems caused by hubs. While a hub operated without any regard for data structure or addressing, a bridge was capable of reading Layer Two information such as Media Access Control addresses. Bridges divide a network into segments, effectively isolating collision domains. This means that devices on one side of the bridge do not directly interfere with those on the other side, which reduces the number of collisions and improves overall performance.
A bridge functions by examining the source and destination MAC addresses of incoming Ethernet frames. It builds a table of MAC addresses and learns which devices are located on which side of the bridge. If the destination MAC address is known and located on the opposite segment, the bridge forwards the frame accordingly. If the destination is on the same side as the source, the bridge filters the frame, preventing unnecessary traffic. This type of intelligence makes the bridge a Layer Two device and distinguishes it from the unintelligent behavior of a hub.
Bridges rely heavily on MAC address tables to function properly. These tables are dynamically learned as the bridge observes traffic. When a device sends a frame, the bridge notes the source MAC and associates it with the corresponding port. When a frame arrives with a known destination, the bridge can forward it directly to the correct segment. This process not only increases efficiency but also introduces a degree of traffic filtering. The bridge avoids flooding the network with unnecessary frames, conserving bandwidth and improving performance.
Typical bridges contain two interfaces, with each port connected to a different network segment. The bridge monitors traffic between these two segments. When a frame arrives on one side, the bridge checks its MAC address table to determine where to send it. If the destination is on the other side, it forwards the frame. If it is on the same side, it does nothing. This two-port logic forms the basis of segment isolation, which was a significant improvement over the broadcast-only behavior of hubs.
Although bridges and switches operate at the same layer of the O S I model, they serve different scales and use cases. A bridge is typically used in small networks and supports only a few interfaces. It is a simple tool for segmenting networks, but it cannot handle large environments effectively. Switches, on the other hand, are more scalable and can manage many ports simultaneously. They also offer faster internal processing, better learning algorithms, and support for advanced features like V L A Ns and spanning tree protocols.
Bridges were commonly found in networks before switches became affordable and widely adopted. In the early days of Ethernet, when cost was a significant factor, bridges offered a practical way to reduce collisions and segment traffic. They were particularly useful in small office or home networks that did not require the complexity or scalability of switches. However, as network demands increased and traffic volumes grew, bridges became less practical and were eventually phased out in favor of switches.
The transition away from hubs and bridges was driven by the need for improved performance, scalability, and traffic management. As network applications became more demanding and the number of connected devices grew, the limitations of legacy devices became clear. Hubs could not prevent collisions or manage bandwidth, while bridges lacked the port density and processing power to scale effectively. The introduction of switches addressed these issues by combining Layer Two functionality with high-speed forwarding and intelligent traffic handling.
For more cyber-related content and books, please check out cyber author dot me. Also, there are other podcasts on Cybersecurity and more at Bare Metal Cyber dot com.
To understand how hubs and bridges differ, it’s essential to compare their operational layers and core behaviors. A hub operates strictly at Layer One, the physical layer of the O S I model. It repeats all electrical signals it receives without any form of decision-making. A bridge operates at Layer Two, the data link layer, and uses MAC address information to make forwarding decisions. This single-layer difference has a major impact on how each device affects network traffic. Hubs treat all data as equal and indiscriminately broadcast it, while bridges analyze traffic to determine the best forwarding path and suppress unnecessary transmissions.
The exam often uses legacy devices to anchor comparison-based questions or network scenario problems. Hubs and bridges might be included as distractors or to test your understanding of why newer devices are superior. In troubleshooting questions, you might be asked to identify why collisions are occurring in a given network or why traffic is flowing inefficiently. Knowing the core limitations of these older devices gives you the insight needed to select the correct answer or diagnose network behavior within the question’s context.
The way these devices handle broadcast traffic also reveals important differences. Hubs do not differentiate between broadcast, unicast, or multicast traffic. All traffic received by a hub is sent to all other ports, regardless of its nature. In contrast, bridges make decisions based on MAC addresses. While bridges still forward broadcast traffic to all ports, they will only forward unicast frames to the appropriate destination port, assuming it has been learned. This selective forwarding dramatically reduces unnecessary traffic between segments and improves overall bandwidth utilization.
Another reason hubs and bridges remain on the exam is their potential appearance in troubleshooting diagrams. These visual representations often include outdated or legacy devices to test your ability to identify performance bottlenecks or improper segmentation. A hub in such a diagram should raise a red flag regarding collisions and traffic flooding. A bridge may prompt analysis around MAC learning and whether traffic is being properly isolated. The certification wants you to associate specific device behaviors with likely problems or inefficiencies in a given network scenario.
Identifying a device’s operational layer within the O S I model is a frequent topic on the exam. Hubs operate at Layer One, meaning they do not interpret any of the information in a frame or packet. They deal only with the signal itself. Bridges function at Layer Two, where they interact with the data link layer information such as MAC addresses. Switches also operate at Layer Two but offer additional capabilities and scalability. For this reason, switches are often described as advanced multiport bridges with enhanced learning and traffic-handling features.
Switches eventually replaced hubs because they solved the collision domain problem. Unlike a hub, which creates a single collision domain for all connected devices, a switch gives each port its own isolated collision domain. This allows multiple devices to transmit data simultaneously without interference. The switch learns MAC addresses dynamically and only forwards frames to the correct destination port. As a result, network performance improves dramatically, especially in busy environments with many active users and devices.
Bridges were also phased out in favor of switches for many of the same reasons. One of the primary limitations of a bridge was its low port count. Most bridges had only two or three ports and were not designed to scale. Switches not only support many ports, but they also offer advanced features like support for virtual local area networks, rapid forwarding of frames, and loop prevention protocols. Switches use application-specific integrated circuits that process frames quickly and efficiently, reducing latency and improving throughput across the network.
From a certification perspective, being aware of legacy devices like hubs and bridges helps form the baseline for understanding how modern networks are designed. These older technologies provide context for the evolution of traffic management, segmentation, and collision avoidance. Understanding how networks were once built allows you to appreciate the capabilities and functions of today’s equipment. This knowledge builds a strong foundation for answering questions about switches, routers, and other advanced devices you’ll encounter both on the exam and in more complex network scenarios.
Ultimately, the characteristics of hubs and bridges can be summarized by their simplicity and their limitations. Hubs repeated all signals to all ports, operated at the physical layer, and offered no traffic management capabilities. Bridges improved the situation by filtering traffic at Layer Two, dividing the network into separate collision domains, and using MAC address tables to make forwarding decisions. While both devices have been replaced in practice, their inclusion on the exam serves as a way to test your foundational knowledge of how traffic flows through a network and how different devices influence that behavior.
Understanding hubs and bridges is not just an academic exercise—it provides a stepping stone to deeper comprehension of how traffic is managed, filtered, and forwarded across a modern network. The certification expects you to know these legacy technologies because they illustrate the problems that newer devices were designed to solve. By mastering this material, you place yourself in a better position to understand the logic behind modern switch behavior, traffic segmentation, and collision domain design. As you move on to other episodes, you’ll continue to build on these foundational ideas.