Modern networks are no longer simple, flat environments—they are segmented, layered, and increasingly software-defined. In this episode, we explore different infrastructure security models, beginning with physical isolation such as air-gapped systems used in critical industrial or military settings, and moving into logical segmentation using VLANs, subnets, and access control mechanisms. We also discuss software-defined networking (SDN), which decouples the control plane from the data plane, allowing for dynamic, programmable traffic flow and policy enforcement at scale. While SDN increases flexibility, it also introduces new security challenges, including the need to protect virtual switches, APIs, and centralized controllers. By comparing on-premise, hybrid, and cloud-native infrastructure models, we show how security principles must adapt to fit the topology and technology. Network architecture isn’t just about performance—it’s a strategic security decision that defines how easily attackers can move, and how effectively defenders can respond.