Physical Topologies
Star topology: all devices connect to a central device (switch or hub). Most common in modern LANs. Easy to troubleshoot — a single cable failure only affects that device. The central device is a single point of failure. If the switch fails, the entire network goes down.
Bus topology: all devices share a single cable (backbone). Legacy topology used in early Ethernet (10BASE5 coax). A single cable break disrupts the entire network. Requires terminators at both ends. Rarely used today but tested on the exam.
Ring topology: devices connect in a closed loop. Data travels in one direction (single ring) or both directions (dual ring for redundancy — FDDI). A single break disrupts single-ring networks. Token Ring and FDDI are ring technologies. SONET uses a dual-ring topology for resilience.
Mesh topology: every device connects to every other device (full mesh) or some devices have multiple connections (partial mesh). Full mesh provides maximum redundancy but requires n(n-1)/2 connections, making it expensive. Partial mesh is a practical compromise. Used in WAN designs and critical network infrastructure.
Hybrid topology: combines two or more topology types. The most common hybrid is a star-bus (individual star segments connected to a backbone bus). Modern enterprise networks are often hierarchical star topologies.
Logical Topologies and Wireless
Logical topology describes how data actually flows, regardless of physical connections. Early Token Ring networks were physically wired as a star (MAU at center) but logically operated as a ring. Modern Ethernet uses a logical bus (CSMA/CD collision detection) despite physical star wiring.
Wireless topology: infrastructure mode uses access points (star topology logically — all clients connect to the AP). Ad-hoc (IBSS) mode: devices communicate directly without an AP (peer-to-peer mesh). Wireless mesh networks use multiple APs with wireless backhaul to extend coverage without running cables to every AP.
Three-Tier Network Architecture
Enterprise networks use a three-tier hierarchical design: Core layer (high-speed backbone, minimal processing), Distribution layer (policy, routing between VLANs, aggregates access layer), Access layer (endpoint connections — where user devices connect). This hierarchy creates a tree-like topology optimized for scalability.
Spine-leaf architecture is the modern data center alternative: every leaf switch connects to every spine switch (partial mesh at the spine), eliminating the three-tier model's bottlenecks. Provides consistent low-latency east-west traffic paths between servers.