I began writing this book as an introduction to the world of networking for new Network Engineers. After a few years on the job, I wanted to compile all of my notes, thoughts, and knowledge in a form that could help out others just starting their careers. I entered my first job with a certain degree of confidence in my knowledge from taking multiple Cisco exams and perhaps an even greater amount of humility about what I didn't know. This work is dedicated to the new guy on the job. It's intended as a hand reference to double check what's been done and to provide helpful hints and advice on how to solve typical problems. It's aiming to cover the topics on the exams that I found critical in my career, and especially covering the things the exams never prepared me for. It assumes some knowledge of basic networking concepts such as IPv4 addressing, subnetting, and the OSI model.The goal is to present this information in an accessible and easy to understand manner, in contrast with other sources such as exam study material or Cisco documentation. It can be used as a reference for code examples, or read cover to cover to familiarize yourself with many topics. Included are many practical labs and configuration examples. I encourage you to build them out, test them, and expand upon them to increase your knowledge.The book is loosely organised into sections covering basic configuration, managing routers and switches, advanced configurations, switching, routing, WAN technologies, and security concepts. Feel free to jump to those you are most interested in or find most useful.