Three-Tier vs Collapsed Core Network Design for the Network+ Exam
Campus network design is usually described in layers, and the exam expects you to know what each layer does and when a smaller design is appropriate. The three-tier model Access layer. Where end devices connect. Provides port density, Power over Ethernet, VLAN assignment, port security and 802.1X authentication. Optimised for cost per port. Distribution layer (aggregation). Aggregates access switches. This is where inter-VLAN routing, access control lists, quality of service policy and route summarisation live. It is the policy boundary of the network. Core layer. High-speed backbone connecting distribution blocks. Its single job is to forward packets as fast as possible, which is why the design rule is that the core does no policy — no ACLs, no filtering, nothing that adds latency or complexity. The organising idea is that each layer has one job, so the design scales predictably and faults are contained. A failure in one distribution block does not affect another. Collapsed c...