Network Fundamentals

Network Fundamentals is the foundation that every other CCNA domain builds on. It is worth 20% of the exam, but in practice you cannot answer routing, switching, security, or automation questions without the vocabulary and skills taught here: what each box in a network does, how cables and frames work, how TCP differs from UDP, how to subnet IPv4 and read IPv6 addresses, and how a switch decides where to send a frame.

If you are new to networking, read this chapter slowly and in order. Later sections assume you understand the earlier ones. Subnetting (1.6) in particular is a skill, not a fact: plan to practice it with pencil and paper until it becomes automatic.