what is a network topology definition

Network topology defines the schematic arrangement of devices, nodes, and connections within a computer network. It determines how data flows between devices, impacting performance, scalability, and reliability. Broadly categorized into physical network topology (the tangible layout of cables and devices) and logical network topology (the virtual path of data flow), understanding these structures is crucial for network design and optimization. In this guide, we explore the types, advantages, and applications of network topologies, including WAN and LAN configurations, to help you choose the best setup for your needs.

The physical network topology

A network’s physical topology is the physical and geometric layout of the network that we can see, such as devices like routers, switches, wireless access points, nodes, and cables. There are several common physical topologies, like point-to-point, ring, bus, star, and mesh. The physical topology has two different categories: WAN and LAN topologies.

Common Physical WAN Topologies

WANs are generally interconnected using these physical topologies:

Point-to-Point

A point-to-point (PTP) network topology connects two nodes directly to one another. Only two devices are involved in a point-to-point connection, with one wire (or air, in the case of wireless) sitting between them. This is the simplest topology in networking, and for this reason, it is a very popular WAN topology. The figure below illustrates the physical point-to-point topology.

• Advantages: Simple, reliable, low cost.
• Disadvantages: Not scalable, limited to two nodes.
• Use Case: Leased lines, serial connections.

Hub and Spoke

A hub-and-spoke network, also known as a star topology, is a traditional and widely used network topology for all types of networks. In this topology, a central site interconnects branch sites using point-to-point links. The central site is known as the hub, and branch sites are known as spokes. Communication between two spokes always travels through the hub. The figure below illustrates the physical hub-and-spoke topology.

• Advantages: Centralized control, moderate scalability.
• Disadvantages: Hub is a single point failure, of increased failure latency for spoke-to-spoke communication.
• Use Case: Branch offices, retail chains.

Mesh Topology

A mesh network is a network topology in which each node relays data for the network. This topology provides high availability but requires that every end system be interconnected to every other system. Therefore, the administrative and physical costs can be very high. Each link is essentially a point-to-point link to the other node. Variations of this topology include a partial mesh in which some but not all end devices are interconnected. The figure below illustrates the physical mesh topology.

• Advantages: High reliability, redundancy.
• Disadvantages: Expensive, complex to manage.
• Use Case: ISP backbones, mission-critical networks.

Physical LAN Topologies

Physical LAN topologies define how devices, such as computers, servers, and switches, are physically connected within a local area network. Below are the most common LAN topologies, their characteristics, and use cases.

Star topology

In a star topology, all devices connect to a central device, typically an Ethernet switch. Data flows through the switch, which manages communication and boosts signals. This topology is widely used in modern LANs due to its scalability and ease of troubleshooting.

Use Case: Office networks, schools, and data centers.

Advantages:

Easy to install and scale by adding devices to the switch.

A single device failure doesn’t disrupt the entire network.

Centralized management simplifies troubleshooting.

Disadvantages:

Central device failure can disable the network.

Requires more cabling than bus or ring topologies.

Extended Star Topology

An extended star topology connects multiple star topologies via additional switches, forming a hierarchical structure. This setup is common in large organizations with distributed networks.

Advantages:

Supports large-scale networks with multiple subnets.

Maintains star topology benefits like scalability.

Disadvantages:

Increased complexity and cabling costs.

Multiple points of failure in switches.

Use Case: University campuses, corporate headquarters.

Bus Topology

In a bus topology, all devices connect to a single coaxial cable (the bus), which is terminated at both ends. Legacy Ethernet networks used this topology, but it’s rare in modern LANs due to limitations.

Advantages:

Inexpensive and simple to set up.

Requires less cabling than star or mesh.

Disadvantages:

A cable break disrupts the entire network.

Difficult to troubleshoot and scale.

Use Case: Small, legacy networks (rarely used today).

Ring Topology

In a ring topology, devices form a closed loop where data travels in one direction. Each device acts as a repeater, boosting the signal. Used in legacy FDDI and Token Ring networks, it’s uncommon in modern LANs.

Advantages:

No need for termination like bus topology.

Predictable data flow reduces collisions.

Disadvantages:

A single device failure can disrupt the ring.

Difficult to add or remove devices.

Use Case: Legacy networks like Token Ring (rare today).

The logical network topology

Logical network topology describes how data flows between devices, independent of their physical connections. It focuses on virtual paths defined by data link layer protocols (e.g., Ethernet, Wi-Fi) and network layer routing. For example, a physical star topology may have a logical bus topology if devices share a single collision domain.

Key Characteristics

• Data Flow: Determines how frames or packets traverse the network.
• Protocols: Governed by protocols like Ethernet, ARP, and IP.
• Media Access Control (MAC): Logical topology influences how devices access shared media (e.g., CSMA/CD in Ethernet).
• Virtual Connections: Logical paths may differ from physical wiring, as in VLANs or VPNs.

Example

In a LAN with a physical star topology using an Ethernet switch, the logical topology might be:

• Point-to-Point: Each device has a dedicated logical connection to the switch.
• Bus: In older hub-based networks, all devices share a logical bus, competing for media access.

Importance

Logical topology impacts network performance, security, and scalability. For instance, VLANs create logical segments on a physical network, isolating traffic for security without additional hardware.

Comparison of Network Topologies

Topology	Type	Scalability	Reliability	Cost	Use Case
Point-to-Point	WAN/LAN	Low	High	Low	Dedicated links (e.g., leased lines)
Hub and Spoke	WAN	Moderate	Moderate	Moderate	Centralized networks (e.g., branch offices)
Mesh	WAN/LAN	High	Very High	Very High	Critical networks (e.g., ISPs)
Star	LAN	High	Moderate	Moderate	Modern LANs (e.g., offices)
Extended Star	LAN	Very High	Moderate	High	Large campuses
Bus	LAN	Low	Low	Low	Legacy networks
Ring	LAN	Low	Moderate	Moderate	Legacy FDDI/Token Ring

How to Choose the Right Network Topology

Selecting the appropriate network topology depends on your organization’s needs, budget, and technical requirements. Consider the following factors:

• Network Size: Small networks may use a star or bus topology, while large networks benefit from an extended star or mesh.
• Budget: Bus and point-to-point topologies are cost-effective, while mesh is expensive due to cabling and maintenance.
• Performance: Mesh offers high redundancy and speed but requires complex management.
• Scalability: Star and extended star topologies are easier to scale than bus or ring.
• Reliability: Mesh and point-to-point provide high reliability, while bus is prone to single-point failures.
• Use Case: For example, ISPs use mesh for backbone networks, while offices prefer a star for simplicity.

Practical Tips

• Assess Requirements: Map out your devices, traffic patterns, and growth plans.
• Consult Experts: Work with network engineers for large-scale deployments.
• Test Configurations: Simulate topologies using tools like Cisco Packet Tracer.
• Plan for Redundancy: Incorporate failover mechanisms in critical networks.

Modern Trends in Network Topology

Network topologies are evolving with advancements in technology. Key trends include:

• Software-Defined Networking (SDN): Separates the control plane from the data plane, enabling dynamic logical topologies managed via software.
• Hybrid Topologies: Combine multiple topologies (e.g., star and mesh) for flexibility and cost efficiency.
• Wireless Topologies: Wi-Fi and 5G networks reduce reliance on physical cabling, creating logical mesh or star topologies.
• Cloud-Based Networking: Virtual topologies in cloud environments (e.g., AWS VPCs) abstract physical infrastructure.
• Zero Trust Architecture: Logical topologies enforce micro-segmentation for security, regardless of physical layout.

These trends highlight the shift toward flexible, scalable, and secure network designs.