This chapter covers network topologies and types, a foundational topic for the CompTIA Network+ N10-009 exam. You will learn the physical and logical arrangements of devices, including bus, star, ring, mesh, and hybrid topologies, as well as wireless and cloud-based network types. Approximately 5-10% of exam questions will touch on topology identification, advantages, disadvantages, and appropriate use cases. Mastering this material is critical because topology choices directly impact network performance, scalability, and fault tolerance—core concepts tested throughout the exam.
Jump to a section
Think of a network topology as a city's road layout. In a bus topology, all buildings (devices) connect to a single main road (the bus). If a car (data packet) needs to go from building A to building B, it drives down the main road, and every building sees it go by, but only the intended recipient picks it up. If the main road is closed (cable break), the whole city is disconnected. A star topology is like a central town square (switch/hub) with roads radiating out to each building. Traffic from A to B goes from A to the square, then out to B. If one road is blocked, only that building is isolated. A ring topology is a circular road with no dead ends. Data travels in one direction, passing each building until it reaches its destination. If a road segment breaks, traffic must be rerouted or stops entirely—similar to a token passing network. A mesh topology is like a city with multiple interconnected roads between every pair of buildings. There are many alternative routes, so if one road is closed, data can take another path. This provides high redundancy but is expensive to build. A hybrid topology combines these: a central star with each branch being a bus or ring, resembling a city with a main hub connected to suburban areas. Wireless topologies (ad hoc, infrastructure) are like walkie-talkies or a cell tower—devices either talk directly peer-to-peer or through a central base station. Understanding these physical and logical layouts helps in designing networks for reliability, cost, and performance—just as city planners choose road layouts based on traffic needs and budget.
What is a Network Topology?
A network topology describes how devices (nodes) are interconnected and how data flows between them. There are two perspectives: physical topology (the actual layout of cables, devices, and physical connections) and logical topology (the path data takes regardless of physical layout). The N10-009 exam tests both, but emphasizes physical topologies for design and troubleshooting.
Bus Topology
In a bus topology, all devices connect to a single central cable called the backbone or bus. Each device has a tap or connector that attaches to the bus. Data transmitted by any device travels in both directions along the bus and is received by all devices—but only the intended recipient processes it.
How it works: When a device sends a frame, it places it on the bus. The electrical signal propagates the entire length. Each device checks the destination MAC address; if it matches, it accepts the frame; otherwise, it ignores it. Terminators at both ends absorb the signal to prevent reflection.
Key components: Coaxial cable (e.g., RG-58 for 10Base2), BNC connectors, terminators (50 ohms for Ethernet).
Advantages: Simple and cheap—requires less cable than star. Easy to extend by adding more cable.
Disadvantages: A single break in the bus brings down the entire segment. Troubleshooting is difficult. Performance degrades as traffic increases because all devices share the same medium. Limited cable length (185 meters for 10Base2).
Exam tip: The exam may ask about terminators and their role in preventing signal bounce. A missing terminator causes reflections and network errors.
Legacy: Bus topologies are obsolete in modern Ethernet but appear in legacy questions. The exam expects you to know why they are no longer used: low fault tolerance and collision domain issues.
Star Topology
The star topology is the most common physical topology in modern LANs. Each device connects directly to a central device—typically a switch (or hub in older networks).
How it works: Data from any device goes first to the central switch. The switch examines the destination MAC address and forwards the frame only to the appropriate port. This creates a point-to-point link between sender and receiver.
Key components: Switch (central point), twisted-pair cabling (Cat5e/6), RJ45 connectors.
Advantages: Easy to install and troubleshoot—if a link fails, only that device is affected. Scalable—adding a new device just requires connecting it to the switch. High performance because each device has its own dedicated bandwidth (full-duplex).
Disadvantages: Single point of failure—if the switch fails, the entire network goes down. Requires more cable than bus.
Exam tip: Know that a hub-based star operates as a logical bus (shared bandwidth, half-duplex) because hubs repeat signals to all ports. A switch-based star is a true star both physically and logically.
Default values: Maximum cable length for twisted-pair Ethernet is 100 meters (328 feet) per segment. Switches have port counts like 8, 24, 48.
Ring Topology
In a ring topology, each device connects to exactly two neighbors, forming a closed loop. Data travels in one direction (unidirectional) or both (bidirectional in a dual ring).
How it works: A token (special frame) circulates around the ring. A device can only transmit when it holds the token. It attaches data to the token and sends it around. Each device regenerates and forwards the signal. When the data returns to the sender, it removes it and releases a new token.
Key components: Token Ring networks used IBM cabling (Type 1) and MAUs (Multistation Access Units). FDDI used fiber optic cable and dual counter-rotating rings.
Advantages: Deterministic performance—no collisions because only one device transmits at a time. Handles heavy traffic well. Dual rings (FDDI) provide redundancy; if one ring breaks, the other takes over.
Disadvantages: A single break in the ring can disable the entire network (unless dual ring or self-healing). Adding or removing a device disrupts the network. Slower than modern switched Ethernet.
Exam tip: The exam may ask about token passing as a media access method. Know that Token Ring operates at 4 or 16 Mbps. FDDI operates at 100 Mbps over fiber.
Legacy: Ring topologies are rarely used today except in some industrial or metropolitan networks. The exam tests them for historical context and contrast with modern topologies.
Mesh Topology
A mesh topology provides multiple paths between devices. In a full mesh, every device connects directly to every other device. In a partial mesh, some devices have multiple connections but not all.
How it works: Each device has a dedicated point-to-point link to every other device (full mesh). Data can take any path; routing protocols determine the best route. If a link fails, an alternate path exists.
Key components: Routers or switches with multiple interfaces, cabling (often fiber for long distances).
Advantages: High fault tolerance—no single point of failure. Excellent redundancy and reliability. Performance is high because traffic can be load-balanced.
Disadvantages: Extremely expensive—cabling and port costs grow exponentially (n(n-1)/2 links). Complexity of configuration and management.
Exam tip: Know the formula for full mesh links: n(n-1)/2. For n=5, that's 10 links. The exam may ask you to calculate the number of links needed. Partial mesh is more practical for WANs.
Use cases: WAN backbones (e.g., ISP core networks), military networks, data center fabrics (e.g., Spine-Leaf architecture is a form of partial mesh).
Hybrid Topology
A hybrid topology combines two or more different topologies into one network. For example, a corporate network might have a star-wired backbone with bus segments in each department.
How it works: Different parts of the network use different physical topologies. The connection points (e.g., switches or routers) bridge the topologies. Data flows through the network according to the logical topology, which may be different from the physical.
Advantages: Flexibility—designers can optimize each segment for cost, performance, or reliability. Scalable—can grow organically.
Disadvantages: Complexity—troubleshooting and management are more difficult. May require more equipment.
Exam tip: The exam may present a scenario and ask you to identify the hybrid topology. Look for multiple topology types in the description.
Wireless Topologies
Wireless networks have their own topologies: Ad hoc (peer-to-peer) and Infrastructure (central access point).
Ad hoc: Devices communicate directly with each other without a central controller. Each device acts as both host and router. Used for temporary networks (e.g., file sharing between laptops).
Infrastructure: Devices connect to a central Access Point (AP), which connects to the wired network. The AP manages authentication, encryption, and traffic forwarding. This is the most common WLAN topology.
Mesh wireless: Some APs can connect wirelessly to each other to extend coverage. This is similar to a wired mesh but uses wireless links.
Exam tip: Know that ad hoc mode is also called IBSS (Independent Basic Service Set). Infrastructure mode uses BSS (Basic Service Set) or ESS (Extended Service Set) for multiple APs.
Cloud and Virtual Network Topologies
Modern networks often include virtual components. Virtual networks are logical networks built on top of physical infrastructure (e.g., VLANs, overlay networks). Cloud topologies refer to how resources are arranged in public/private clouds (e.g., VPC, subnets, availability zones).
How it works: Hypervisors or SDN controllers create virtual switches and routers. Virtual machines connect to virtual ports. Traffic is encapsulated (e.g., VXLAN) and transported over the physical network.
Key components: Virtual switches (vSwitch), virtual routers, tunnels (GRE, VXLAN).
Advantages: Flexibility—topology can be changed without rewiring. Better resource utilization.
Exam tip: The exam may ask about VLANs as a logical topology within a physical star. Understand that VLANs create separate broadcast domains.
Comparison of Topologies
| Topology | Fault Tolerance | Cost | Scalability | Performance | |----------|----------------|------|-------------|-------------| | Bus | Low | Low | Low | Low (shared) | | Star | Medium (switch failure) | Medium | High | High (switched) | | Ring | Low (single ring) | Medium | Medium | Medium | | Mesh | High | Very High | High | Very High | | Hybrid | Varies | Varies | Varies | Varies |
How Topologies Interact with Other Technologies
Ethernet: Typically uses star or extended star (tree) topology. Switches create a star; multiple switches can be connected in a hierarchical star.
Spanning Tree Protocol (STP): Prevents loops in switched networks with redundant links (which create a mesh-like topology). STP block ports to ensure a loop-free logical topology.
Routing: In mesh topologies, routers use routing protocols (OSPF, EIGRP) to determine best paths. In a star, routing is simpler.
Wireless: Access points create a star topology; if multiple APs are used, they may be connected via a wired backbone (star) or wirelessly (mesh).
Configuration and Verification Commands
While topologies are physical, you can verify them with:
`show interfaces` – see connected links.
`show cdp neighbors` (Cisco) – discover directly connected devices.
`show spanning-tree` – view logical topology for STP.
`traceroute` – see the path packets take (logical topology).
Example output:
Switch# show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone
Device ID Local Intrfce Holdtme Capability Platform Port ID
Router1 Gig0/1 172 R ISR4331 Gig0/0
Switch2 Gig0/2 162 S WS-C2960 Gig0/1Summary
Network topologies define the structure of a network. The N10-009 exam expects you to identify topologies from diagrams, know their advantages/disadvantages, and understand how they affect performance and fault tolerance. Focus on star (most common), mesh (high redundancy), and hybrid designs. Remember that logical topology may differ from physical—e.g., a physical star can be a logical bus if using a hub.
Identify the Physical Layout
Start by drawing or visualizing how devices are physically connected. Look at the cabling: are all devices connected to a central point (star), daisy-chained (bus), or in a closed loop (ring)? In a star, each device has its own cable to a switch. In a bus, a single cable runs from device to device with terminators at ends. In a mesh, you see multiple connections per device. This step is critical because the exam often shows a diagram and asks you to name the topology.
Determine the Logical Path
Next, consider how data actually flows. Even if the physical layout is star, the logical topology could be bus (if using a hub) or star (if using a switch). For ring topologies, the logical path is circular. For mesh, the logical path depends on routing. Use tools like traceroute to see the path. The exam may ask about logical vs. physical differences—for example, a physical star with a hub behaves as a logical bus.
Analyze Fault Tolerance
Assess what happens when a single link or device fails. In a bus, a cable break disrupts all devices beyond the break. In a star, only the device on that link fails. In a ring, a single break disables the entire ring (unless dual ring). In a full mesh, no single failure isolates any device. This analysis helps choose a topology for high availability. The exam often asks: 'Which topology provides the highest fault tolerance?' Answer: full mesh.
Evaluate Scalability and Cost
Consider how easily the network can grow. Star topologies are highly scalable—just add more ports to the switch or cascade switches. Bus topologies have length and device limits (e.g., 30 devices per segment for 10Base2). Mesh scales poorly due to exponential link growth. For n=10, full mesh requires 45 links. Cost is directly proportional to number of links and ports. The exam may ask you to calculate links or compare costs.
Select Appropriate Topology
Based on requirements (budget, reliability, performance), choose a topology. For a small office, star is best. For a data center, consider leaf-spine (a type of partial mesh). For a legacy exam question, you might choose bus for simplicity. Always justify based on fault tolerance, cost, and scalability. The exam scenario will give clues: 'Which topology is most cost-effective for a small network?' Star.
Enterprise Scenario 1: Corporate LAN with Star Topology
A medium-sized company with 200 employees uses a star topology. Each department has a 48-port switch connected via fiber uplinks to a core switch. This design provides easy troubleshooting: if a user's port fails, only that user is affected. The network team uses show interfaces and show spanning-tree to monitor. Misconfiguration example: A junior admin connected two core switches with two cables to increase bandwidth, but forgot to enable link aggregation. This created a loop, causing a broadcast storm. STP blocked one link, but performance didn't improve. The fix was to configure EtherChannel. The team learned to always verify STP state after cabling changes.
Enterprise Scenario 2: WAN with Partial Mesh
A multinational corporation connects five regional offices. A full mesh would require 10 dedicated WAN links (expensive). Instead, they use a partial mesh: each office connects to two others, and to a central hub. This provides redundancy without full mesh cost. For example, if the link between London and New York fails, traffic routes via the hub (e.g., London to Frankfurt to New York). They use OSPF for dynamic routing. Common mistake: Not enough bandwidth on hub links, causing congestion during failover. They monitor link utilization and upgrade when >70%.
Enterprise Scenario 3: Data Center with Leaf-Spine Topology
A large data center uses a leaf-spine architecture, which is a form of partial mesh. Each leaf switch connects to every spine switch, but spines do not connect to each other. This provides predictable east-west traffic and high bandwidth. For 40 leaf switches and 4 spine switches, there are 160 links. The network team uses BGP for routing. Misconfiguration: Setting incorrect MTU values caused packet drops. They use ping with DF bit to test MTU. The key performance consideration is oversubscription ratio (typically 3:1 to 5:1).
What N10-009 Tests
Objective 1.6: 'Explain the concepts and characteristics of routing and switching.' This includes topology identification, advantages/disadvantages, and appropriate use cases. Expect 2-3 questions on topologies (5-10% of exam). The exam will test: - Physical vs. logical topology: Understand that a hub creates a logical bus even if physically star. - Fault tolerance: Know which topology survives a single link failure. - Scalability: Which topology scales best? Star (easy) vs. mesh (hard). - Cost: Bus is cheapest; mesh is most expensive. - Legacy technologies: Token Ring, FDDI, 10Base2.
Common Wrong Answers
'Bus topology provides high fault tolerance' – Wrong. A single break breaks the entire segment. Candidates confuse bus with mesh.
'Star topology uses a hub for best performance' – Wrong. Hubs cause collisions; switches provide dedicated bandwidth. The exam expects you to know hubs vs. switches.
'Ring topology is the most scalable' – Wrong. Adding a device disrupts the ring. Star scales better.
'Full mesh requires n-1 links per device' – True for each device, but total links is n(n-1)/2. Candidates may forget the division by 2.
Specific Numbers and Terms
10Base2: 185 meters, 30 devices per segment, 50-ohm terminators.
Token Ring: 4 or 16 Mbps.
FDDI: 100 Mbps, dual ring, 200 km max circumference.
Star: max 100 meters per segment (twisted pair).
Full mesh formula: n(n-1)/2.
Edge Cases
Hybrid topology: The exam may describe a network with a star backbone and bus segments. Know that this is hybrid.
Wireless mesh: APs can form a wireless mesh without wired backhaul.
Logical ring: FDDI uses a dual ring physically, but logically it's a ring. Token Ring uses a physical star with MAU but logical ring.
How to Eliminate Wrong Answers
If the question mentions 'single point of failure', eliminate bus and single ring. Star has a single point (switch), but the exam may ask 'which has no single point of failure?' Answer: full mesh.
If cost is a concern, eliminate mesh. If simplicity is key, choose star.
If deterministic access is needed (no collisions), choose ring (token passing).
For wireless, ad hoc is peer-to-peer; infrastructure uses AP.
Focus on understanding the mechanism behind each topology—not just memorizing lists. The exam rewards deep understanding.
Physical topology is the actual layout; logical topology is the data path.
Star is the most common physical topology for modern LANs.
Bus topology uses terminators to prevent signal reflection.
Full mesh requires n(n-1)/2 links for n devices.
Ring topologies use token passing to avoid collisions.
Hybrid topologies combine two or more different topologies.
Wireless ad hoc (IBSS) has no central AP; infrastructure (BSS) uses an AP.
These come up on the exam all the time. Here's how to tell them apart.
Star Topology
Each device connects to a central switch/hub.
Fault isolation: a single link failure affects only that device.
Easy to troubleshoot and expand.
Requires more cable than bus.
Performance is high with switches (dedicated bandwidth).
Bus Topology
All devices share a single backbone cable.
A single break in the backbone disrupts the entire segment.
Difficult to troubleshoot; requires terminators.
Uses less cable than star.
Performance degrades with increased traffic (shared medium).
Mistake
A star topology uses a hub, so it's a logical star.
Correct
A hub-based star is a logical bus because all devices share the same collision domain. Only a switch creates a logical star with separate collision domains.
Mistake
Ring topologies are obsolete and not tested.
Correct
The exam includes legacy ring topologies like Token Ring and FDDI. You must know their characteristics and media access method (token passing).
Mistake
Mesh topology requires every device to connect to every other device.
Correct
That's full mesh. Partial mesh is more common. The exam may ask about both. Know the difference.
Mistake
Bus topology is still widely used in modern networks.
Correct
Bus topology is largely obsolete in Ethernet due to low fault tolerance and performance issues. It appears only in legacy exam questions.
Mistake
Wireless ad hoc networks are the same as infrastructure mode.
Correct
Ad hoc (IBSS) has no central AP; devices communicate directly. Infrastructure (BSS/ESS) uses an AP. They are different topologies.
Reveal each answer, then mark whether you got it right. Score 60%+ to unlock the next chapter.
Physical topology describes how devices are physically connected (cables, ports). Logical topology describes how data flows. For example, a network with a hub has a physical star layout but a logical bus because all devices share the same collision domain. The exam tests your ability to distinguish between the two. Always ask: 'What does the cabling look like?' vs. 'How does data travel?'
Full mesh topology provides the highest fault tolerance because every device has a direct connection to every other device. A single link failure does not isolate any device; data can take an alternate path. However, it is expensive. For a practical compromise, partial mesh or star with redundant switches offers good fault tolerance at lower cost.
For twisted-pair Ethernet (e.g., Cat5e, Cat6), the maximum segment length is 100 meters (328 feet). This is a standard specification from IEEE 802.3. Exceeding this length can cause signal attenuation and errors. For longer distances, use fiber optic cabling or repeaters/switches to extend the network.
Token passing is a media access control method where a special frame called a token circulates around the network. A device can only transmit when it holds the token. This eliminates collisions. It is used in ring topologies like Token Ring (IEEE 802.5) and FDDI. The exam may ask about token passing as a deterministic access method.
A hybrid topology combines two or more different topologies. For example, a company might have a star-wired backbone with switches connected in a star, and each department uses a bus topology with daisy-chained devices. Another example is a wireless mesh network where some APs are wired (star) and others connect wirelessly (mesh).
Star topology offers better fault tolerance: if one cable fails, only that device is affected, not the whole network. It is easier to troubleshoot because each device has its own link. Adding or removing devices does not disrupt the network. With switches, each device gets dedicated bandwidth, improving performance. The main disadvantage is dependency on the central switch.
The formula is n(n-1)/2, where n is the number of devices. For example, 5 devices require 5*4/2 = 10 links. This exponential growth makes full mesh impractical for large networks. The exam may ask you to calculate the number of links or compare to partial mesh.
You've just covered Network Topologies and Types — now see how well it sticks with free N10-009 practice questions. Full explanations included, no account needed.
Done with this chapter?