A layered model provides the foundation for your understanding of networks. The stronger you build this foundation, the more information you will be able to easily learn and retain. When you learn, teach, troubleshoot, and tackle network configuration, the Open Systems Interconnection (OSI) model and the Transmission Control Protocol/Internet Protocol (TCP/IP) model should guide your plan of attack. Not surprisingly, the CCENT exam tests your ability to describe networks using a layered model. This section includes topics covered in Chapter 6 of CCNA Discovery 1 and Chapter 2 of CCNA Discovery 2.