What is network design principles (hierarchical model)?
Answer
The hierarchical network design model (Cisco three-tier model) organizes the network into logical layers, each with a specific role. Access layer: connects end devices (workstations, IP phones, APs) to the network — Layer 2 switches with port security, 802.1X, PoE. Focus: user connectivity and policy enforcement. Distribution layer: aggregates access layer switches and provides inter-VLAN routing, policy (ACLs, QoS), and redundancy — Layer 3 switches. Acts as the boundary between Layer 2 access and Layer 3 core. Core layer: the high-speed backbone connecting distribution layers and providing connectivity to the data center, WAN, and Internet. No complex policies — pure speed and availability (redundant Layer 3 switches or routers). Modern data centers use a leaf-spine (Clos) architecture: every leaf switch connects to every spine switch — predictable latency, no oversubscription, scales by adding spine/leaf pairs. Good design principles: modular (add capacity without redesign), hierarchical (scalable), redundant (no SPOF), summarizable (hierarchical addressing allows route summarization).