DO NOT design your network like this!! // FREE CCNA // EP 6

Network design fails when it relies on single points of failure—especially daisy-chained switches that can take down entire segments when one cable or device breaks. The core fix is to build redundancy intentionally: use a structured architecture that keeps critical traffic flowing even if a link or switch goes offline, instead of stacking devices in a way that turns one failure into widespread downtime.

A common “home-network” mistake shows up in small businesses as they grow: one router connects to a switch, then another switch is added by connecting switch-to-switch, and then again. It works until a single cable gets chewed through or a switch fails. At that point, every device hanging off the affected switch loses connectivity, which is why the design is described as having “single points of failure.” In a business setting, that kind of outage translates directly into lost time and money.

To reduce those risks, the lesson pushes toward redundancy plus a tiered layout. The first architecture is a two-tier model: access layer switches connect end devices, while distribution layer switches act as the intermediary that routes and manages traffic between access and the router. The distribution layer is treated as the “workhorse” because it handles more than forwarding—often including VLAN routing, route filtering, ACLs, IP security policies, summarization, and next-hop redundancy. Because it carries more traffic, it needs more capacity than access switches, which is why the distribution layer is described as “beastly” and typically built with higher-end hardware.

The two-tier model still leaves room for failure if only one distribution switch or one uplink exists, so the recommended approach is to add redundancy at the right places: multiple distribution switches, multiple links to each, and multiple connections up to the router. That improves resilience, but it also increases cost because higher-end multi-layer switches and routers are expensive.

When networks expand beyond a single campus building—multiple buildings, lots of inter-building traffic, and more endpoints—the architecture often shifts to a three-tier model. In this design, a dedicated core layer sits above distribution. The core is built for low latency, high reliability, and high throughput, serving as the backbone that aggregates traffic from distribution switches. Distribution then connects access to the core, while routers connect into the core as well. The result is a cleaner, more scalable campus design that avoids the messy, full-mesh connectivity that becomes unmanageable as the network grows.

An important nuance is that the “core” role doesn’t always disappear in two-tier designs; it can be collapsed into the distribution layer. This “collapsed core” model is common in practice because it can be sufficient for many organizations—especially those with one main corporate office and limited campus complexity. The trade-off is that three-tier designs become more attractive when the campus spans many buildings and needs consistent, high-speed connectivity.

By the end, the practical takeaway is to identify what architecture a real organization uses—two-tier, three-tier, or a hybrid—and compare it to the failure modes discussed: single points of failure, daisy-chaining, and where redundancy is (or isn’t) built into the design.