Modern networks rarely connect physical hosts directly. This chapter covers server virtualization (hypervisors and VMs), containers (Docker / Kubernetes), and VRFs (virtual routing tables on a single router) — and how they show up in modern networks.
A hypervisor runs multiple guest operating systems on one physical host, each in its own virtual machine. Each VM has its own kernel and emulated hardware (vNIC, vDisk). Type 1 hypervisors (ESXi, Hyper-V, KVM) run directly on hardware; Type 2 (VirtualBox, Workstation) run on top of a host OS.
On the network side, VMs share the host's physical NIC through a virtual switch (vSwitch) — software that does L2 switching inside the hypervisor. This is why a 'server' on a network diagram might map to dozens of VMs on one box.
Containers (Docker, containerd, Podman) package an application with its dependencies and run as isolated processes that share the host's kernel. They boot in milliseconds and use a fraction of the memory of VMs. Kubernetes orchestrates thousands of containers across a cluster, scheduling them onto worker nodes and stitching them together with overlay networks.
From a network perspective: each container typically has a virtual interface (veth pair) bridged or routed onto the host's network namespace; pod-to-pod communication is handled by a CNI plugin (Calico, Cilium, Flannel).
2 more sections in this chapter, plus a 2-question quiz.
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