This book is the official supplemental textbook for the Working at a Small-to-Medium Business or ISP course in the Cisco® Networking Academy® CCNA® Discovery curriculum version 4.1. The course, the second of four in the new curriculum, teaches networking concepts by applying them to a type of network you might encounter on the job in a small-to-medium business or ISP. After successfully completing the first two courses in the CCNA Discovery curriculum, you can choose to complete the CCENT® (Cisco Certified Entry Network Technician) certification exam, which would certify that you have developed the practical skills required for entry-level networking support positions and have an aptitude and competence for working with Cisco routers, switches, and Cisco IOS® Software.