Router
An extensive introduction to Cisco router routing basics, explaining how routers function as Layer 3 network devices to connect different networks, such as LANs and WANs. It details the router's hardware and memory components, along with the different command-line interface (CLI) modes used for configuration. Furthermore, the text outlines the various Cisco operating systems (IOS, IOS XE, and IOS XR), distinguishing between modular and fixed router models, including specialized types like ISR, ASR, and CRS. Finally, the document covers essential security configurations, such as passwords, Telnet, and SSH, and thoroughly differentiates between routed protocols (data traffic) and routing protocols (information exchange), categorizing the latter into static, default, and dynamic routing (IGP and EGP) along with their metrics and concepts like Administrative Distance (AD) and Autonomous Systems (AS).