Book excerpt: Networking Essentials Companion Guide is the official supplemental textbook for the Networking Essentials course in the Cisco Networking Academy. Networking is at the heart of the digital transformation. The network is essential to many business functions today, including business-critical data and operations, cybersecurity, and so much more. A wide variety of career paths rely on the network, so it's important to understand what the network can do, how it operates, and how to protect it. This is a great course for developers, data scientists, cybersecurity specialists, and other professionals looking to broaden their networking domain knowledge. It's also an excellent launching point for students pursuing a wide range of career pathways—from cybersecurity to software development to business and more. The Companion Guide is designed as a portable desk reference to use anytime, anywhere to reinforce the material from the course and organize your time. The book's features help you focus on important concepts to succeed in this course: * Chapter objectives: Review core concepts by answering the focus questions listed at the beginning of each chapter. * Key terms: Refer to the lists of networking vocabulary introduced and highlighted in context in each chapter. * Glossary: Consult the comprehensive Glossary with more than 250 terms. * Summary of Activities and Labs: Maximize your study time with this complete list of all associated practice exercises at the end of each chapter. * Check Your Understanding: Evaluate your readiness with the end-of-chapter questions that match the style of questions you see in the online course quizzes. The answer key explains each answer.