Case studies

Real infrastructure, studied on its own terms. Company cases describe only publicly documented architecture and cite every source; pattern studies teach the designs the exam expects you to reach for.

Enterprise DNS, DHCP, and NTP: designing and troubleshooting the three services that make a network usableA client that cannot get an address, resolve a name, or trust its clock is off the network. Here is how the three core services fit together and how to find the one that broke.3.4 5.3Site-to-site IPsec VPN between headquarters and a branch officeTwo private LANs, one untrusted internet in between, and a pair of gateways that make the whole thing behave like a single routed network.3.5 1.4Three-tier campus design: access, distribution, and coreWhy enterprise LANs are built as three layers, and what each one is and is not allowed to do.1.6 2.2VLAN segmentation, inter-VLAN routing, and 802.1Q trunkingHow one physical switch becomes many isolated networks, and how a single trunk and a handful of SVIs let those networks talk again on your terms.2.2 2.1