Bus topology is a network layout where all devices connect to one shared cable, called the backbone or bus. It is one of the oldest and simplest ways to hook things up in computer network environments. You won't find bus topology running many modern office networks, star and mesh are far more common now. But it hasn't completely disappeared. You might still see it in specific spots like industrial control systems, maybe some lingering old-school Ethernet setups, or even parts of certain rural broadband networks. Its main draws? Simplicity and low cost, which make it okay for very specific jobs.
Explore what we discuss in our article or skip straight to the gear, protocols, or modern workarounds that matter to your setup.
Think of bus topology like setting up seats along a single park bench. All the devices (nodes) connect to one main cable, often called the "bus" or "backbone." When one device sends data, it travels along that whole cable, and every device sees it. Each device checks the packet's address to see if it's the intended recipient. If not, it ignores it. To stop signals from bouncing back and causing problems, you stick special plugs called terminators on both ends of the main cable.
Key things to remember: one shared cable, data broadcasts to everyone, needs terminators, usually half-duplex (only one device talks at a time), and the nodes themselves don't boost the signal.
This setup was popular way back in the early Ethernet days (think 70s and 80s) because it was cheap and easy. But as networks got bigger and needed more speed and reliability, star and mesh topologies pretty much took over.
In a bus topology, a device sends data as an electrical signal along the backbone cable, reaching all connected nodes simultaneously. Each node examines the destination address (like the MAC address) in the data packet and either processes it or discards it. To manage access to the shared cable and avoid simultaneous transmissions, networks using bus topology often employ CSMA/CD (Carrier Sense Multiple Access with Collision Detection). This method helps detect collisions and triggers devices to retry transmissions.
Terminators, typically 50-ohm resistors, are placed at each physical end of the backbone cable to absorb signals and prevent them from reflecting back, which could cause interference. While effective for small networks, performance tends to degrade noticeably with more than about 10 nodes due to the increased probability of collisions and the limitations of the shared bandwidth (often below 5 Mbps on older 10BASE2 Ethernet segments).
A bus topology diagram shows a single horizontal backbone cable running straight across, with each device tapped into that cable through T-connectors or similar adapters. Both ends of the backbone are terminated with special plugs. The whole thing looks like a straight line with branches hanging off it, fundamentally different from star topology's hub-and-spoke pattern or ring topology's closed loop.
Here's what to look for in a bus network diagram:
The simplicity of the diagram reflects the simplicity of the network itself. That single line is both its biggest advantage (cheap, easy to set up) and its biggest weakness (one cut takes everything down).
The main bits and pieces of a bus network include:
Bus topology has a distinct set of characteristics that separate it from other network topologies. Whether you're studying for a certification exam or evaluating a legacy network, these are the defining features:
| Feature | Description |
| Shared medium | All devices share a single backbone cable for communication |
| Broadcast transmission | Data sent by one device reaches every other device on the bus |
| Half-duplex operation | Only one device can transmit at a time; others must wait |
| Linear layout | Devices connect along a straight cable path, no loops |
| Passive nodes | Devices don't regenerate or boost the signal they just tap into it |
| Termination required | Both ends of the cable need terminators to prevent signal reflection |
| Single collision domain | All devices compete for the same bandwidth using CSMA/CD |
| No central device | Unlike star topology, there's no switch or hub managing traffic |
These characteristics make bus topology cheap and simple for small setups but fundamentally limited when networks need to scale, handle heavy traffic, or provide fault tolerance.
Bus topology relies on certain rules (protocols) to manage the shared cable:
As mentioned, this was the collision management system for early Ethernet (like 10BASE2 "ThinNet"). Listen, send, detect collision, back off, retry. Simple, but inefficient under load.
Common in industrial settings (factories, power plants). It's often run over RS-485 wiring in a bus layout. A "master" device polls "slave" devices (sensors, actuators) along the bus. Slower speeds (like 9600 bps) are typical, but it's reliable for industrial distances. Check Modbus.
Used in automation. Lets devices talk directly without a central computer. Uses twisted-pair cabling in a bus and has good built-in error handling. Speeds can reach up to 1 Mbps over shorter distances. Learn more.
Used for cable internet. While the whole cable network (HFC) isn't just a bus, the final coax cable run connecting multiple homes in a neighborhood often acts like one. DOCSIS manages how users share bandwidth on that coax segment.
The specific hardware depends on the type of bus network:
For 10BASE2 (ThinNet) Ethernet: RG-58 coax cable, BNC T-connectors for each device, 50-ohm BNC terminators at the ends. Network cards needed BNC ports. Mostly museum stuff now.
For 10BASE5 (ThickNet) Ethernet: Even older! A thicker, less flexible coaxial cable (like RG-8) is used. Devices connect using "vampire taps" that physically pierce the cable insulation to contact the core conductor. These taps connect via drop cables to an AUI (Attachment Unit Interface) port on the network device. This is largely obsolete but might exist in legacy installations.
For Industrial Fieldbus (e.g., RS-485 Modbus): Shielded twisted-pair cable (often 120-ohm impedance) is typically used instead of coax. Each device needs an RS-485 transceiver. Termination resistors (usually 120 ohms) are required at both ends of the bus. "Fail-safe" biasing resistors might also be used to ensure the line state is defined when no device is transmitting.
For Controller Area Network (CAN Bus): 120-ohm twisted-pair cable is standard. Each node requires a CAN controller/transceiver. Like RS-485, 120-ohm termination resistors are placed at each end of the bus. CAN includes more sophisticated error handling at the hardware level compared to basic RS-485.
Because everyone connects to the same wire, security is a big concern. Any device on the bus can potentially see all the traffic. If data isn't encrypted, anyone connected could potentially sniff packets. To lock it down:
Encrypt Data: Use IPsec for site-to-site or TLS for app-layer security e.g., Modbus over TLS.
Isolate Traffic: In modern setups, VLANs on a switch mimic bus behavior while segmenting nodes.
Physical Security: In purely coax-based bus environments, physically securing the cable plant and T-connectors can reduce unauthorized taps.
Troubleshooting is another pain point. There's no central hub to check. If something breaks (a bad cable section, loose T-connector, missing terminator), the whole segment might go down. You often end up having to manually check connections along the entire bus path.
On modern networks where a bus segment might connect to a switch, you could use port mirroring (SPAN) or NetFlow to get some visibility into traffic on that segment.
monitor session 1 source interface FastEthernet0/1 ! Monitors the bus-connected port monitor session 1 destination interface FastEthernet0/10 ! Sends traffic to analyzer
Pure bus topology isn't native to modern Cisco gear, but you can mimic it. Use a switch with a single VLAN to emulate a shared domain.
VLAN Isolation:
interface vlan 10 ip address 192.168.1.1 255.255.255.0 no shutdown
Basic Switch Port Setup:
interface FastEthernet0/1 switchport mode access switchport access vlan 10 spanning-tree portfast
If you connect multiple switches set up like this, you absolutely need Spanning Tree Protocol (STP) (preferably Rapid PVST+) enabled to prevent loops.
spanning-tree mode rapid-pvst
This creates a shared broadcast domain logically similar to a physical bus, but you get the better performance and management features of a switch. You can practice these kinds of setups in CloudMyLab's hosted GNS3 or EVE-NG labs using real Cisco IOS images. Check Cisco STP Overview.
Despite its limitations, bus topology finds application in:
Not entirely. Classic Ethernet bus topology (10BASE2, 10BASE5) is effectively dead for general-purpose networking. Star topology with managed switches took over because it solves every major problem bus topology has: fault isolation, scalability, diagnostics, speed.
But the bus architecture itself? It's alive and well in places most people don't think about:
The pattern is consistent: where you need simple, deterministic, low-bandwidth communication bus topology remains a solid choice. A temperature sensor reading every 5 seconds doesn't need gigabit Ethernet. It needs predictable, cheap, and reliable. That's bus.
For anything involving office LANs, campus networks, or data centers, the answer is clear: use star or mesh topology.
Bus topology shows up on both CompTIA Network+ and Cisco CCNA certification exams. It's a fundamental networking concept that exam creators test because understanding legacy topologies reveals why modern networks are designed the way they are.
What the exams typically ask about:
Exam prep tips:
If you're studying for CCNA or Network+ and want hands-on practice, CloudMyLab's hosted labs let you build virtual networks using real Cisco IOS images. You can emulate bus-like behavior with VLANs and explore how switching changed everything about network design.
Bus topology originated when 10 Mbps was considered fast. Today's networks typically require hundreds of Mbps or even multiple Gbps per device. The single, shared cable of a bus topology becomes a severe bottleneck for modern applications involving large file transfers, streaming media, or numerous concurrent connections. Performance suffers drastically even with a small number of devices under contemporary data loads.
Understanding how bus compares to other network topologies helps in network design. It is crucial to balance cost, fault tolerance, scalability, and complexity.
Bus topology is the simplest and cheapest for linear layouts but suffers from poor scalability, low fault tolerance, and significant performance limitations.
Ring topology offers predictable data flow, useful for MANs or industrial systems, but requires redundancy (dual rings) for reliability.
Star topology is easy to manage and troubleshoot due to its central connection point (switch/hub), making it standard for modern LANs.
Mesh networks provide high reliability through multiple paths between nodes, ideal for critical infrastructure but complex and costly.
Modern networks often combine these topologies into hybrid network designs that leverage each approach's strengths while minimizing weaknesses.
| Feature | Bus | Ring | Star | Mesh |
| Fault Tolerance | Poor (single backbone cut breaks all) |
Good if dual ring (redundant) Poor if unidirectional |
Central hub is a single point of failure |
Excellent (multiple paths) |
| Scalability | Limited (beyond ~10 nodes collisions spike) |
Moderate (adding nodes carefully) |
Excellent (easy to add devices at hub) |
Poor (full mesh) or moderate (partial mesh) |
| Cost | Low (single cable) |
Moderate (specialized hardware) |
Low to Moderate (standard switches) |
High (many links/cables) |
| Performance | Variable (collisions can slow traffic) |
Predictable (token-based or ring protocols) |
Variable (depends on hub performance) |
Excellent (parallel paths, load distribution) |
| Implementation Complexity | Low (quick but limited) |
Moderate (requires ring connections) |
Low (simple to deploy/troubleshoot) |
High (significant cabling and config) |
| Latency | Variable (collision domain) |
Grows with node count (each node adds hop) |
Consistent (generally one hop to hub) |
Low (direct connections if fully meshed) |
| Hardware Requirements | Very simple (coax cable, T-connectors) |
Specialized ring-capable devices/cables (e.g., fiber rings) |
Standard switches or hubs | Standard equipment but more of it |
| Best Used For | Small, simple setups or niche industrial automation |
Industrial setups, MANs, fiber optic deployments |
Home networks, small offices, classroom networks |
Critical infrastructure (data centers, financials) |
Need to see how bus topology behaves, maybe test legacy protocols or industrial setups like Modbus over RS-485? CloudMyLab provides hosted labs using EVE-NG, GNS3, and Cisco Modeling Labs (CML). You can build virtual networks that mimic bus behavior, observe collisions, or practice security configs without needing old coax cables or specific hardware.
Here are some helpful resources for learning more:
Its low cost and straightforward setup make it ideal for very small, budget-conscious networks or simple industrial scenarios. You need just a cable, some T-connectors, and two terminators.
Everything stops. That single cable is the lifeline, so a cut or fault knocks out all communication until it's fixed. There's no redundancy or failover path.
Yes, just tap in more devices, but watch out, too many (say, over 10) clog the line with data crashes, slowing things down because of CSMA/CD collision overhead.
Not in office LANs, but it's everywhere in industrial automation (CAN bus, Modbus), commercial building systems (BACnet), cable broadband (DOCSIS), and aerospace (MIL-STD-1553). The bus architecture persists where simplicity and deterministic communication matter more than speed.
It uses CSMA/CD: devices listen, send when clear, and retry if signals collide. Think of it like taking turns talking, but messier with more voices. After each collision, devices wait a random backoff period before retrying.
Little plugs (like 50-ohm resistors) at each end of the cable that soak up signals so they don't bounce back and garble the data. Without terminators, reflected signals create interference that makes the network unusable.
Coaxial cable, tough against noise, it's the classic pick for keeping signals clean over a shared line. RG-58 (50-ohm) for 10BASE2 ThinNet is the most common. Industrial bus networks typically use shielded twisted-pair (120-ohm) instead.
It depends on the standard. For 10BASE2 (ThinNet): 185 meters per segment. For 10BASE5 (ThickNet): 500 meters per segment. For RS-485 industrial bus (Modbus): up to 1,200 meters at 9,600 bps. Repeaters can extend these distances by connecting multiple segments.
Star topology solved every major bus problem: fault isolation (one cable fails, only one device goes down), scalability (add a port to the switch), diagnostics (port LEDs, log messages, show interface), and speed (dedicated bandwidth per port instead of shared). The switch made bus obsolete for LANs.
Bus uses a single shared cable where all devices compete for bandwidth. Star uses a central switch with dedicated cable runs to each device. Star is more reliable (one cable failure doesn't kill the network), faster (no collisions with full-duplex switches), and easier to manage, which is why it's the standard for modern LANs.
There's no easy way. With no central device providing diagnostics, you're stuck testing connections manually. Start from the terminators and work inward. Use a cable tester or TDR (Time-Domain Reflectometer) to find breaks. Check every T-connector, a single loose one can take down the entire segment.
Yes. Both CompTIA Network+ and Cisco CCNA test bus topology concepts. Expect questions about CSMA/CD, terminators, cable types (RG-58, RG-8), collision domains, and why star topology replaced bus. Understanding the "why" behind the evolution is more important than memorizing obsolete specs.