Book excerpt: This is Cisco's authorized, self-paced, foundation learning tool for the latest version of the Cisco DESGN exam, required for the current CCDA certification. It brings together the core knowledge professionals need to design routed and switched enterprise network infrastructures within Cisco's best-practice Preparing, Planning, Designing, Implementing, Operating, and Optimizing (PPDIOO) framework. As an Authorized Self-Study Guide, this book fully reflects the content of the newest version of the Cisco DESGN course. Real-world scenarios and a running case study illustrate and reinforce key concepts, and chapter-ending questions help readers assess their understanding as they prepare for the exam. Based on the popular Second Edition, this update fully reflects new developments, including: " Borderless networks, including security issues " Data center virtualization " Collaboration for enterprise and commercial customers.