Internet Protocol version 4 (IPv4)
Binary Scale, Powers of 2, Octets and Classes, & Default / CIDR Subnet Masks
September 1981 was a defining year. Not only was I six months old, but RFC 791 — the formal specification for IPv4 — was published in California for the Defense Advanced Research Projects Agency (DARPA). While many other protocols have existed for addressing devices on a network (NETBEUI, IPX/SPX, Token‑Ring, and others), IPv4 has remained the “gold standard” for more than 40 years.
As most already know (and those who don’t will now), IPv4 is showing its age. It’s saturated, limited, and largely replaced by IPv6. I won’t cover IPv6 here, but I will cover everything you need (or want) to know about how IPv4 works — both now and in the upcoming video lesson.
Attached to this post is a PDF version of the full presentation, including all slides and their notes. I built this chapter using the same linear, mapped‑learning format I used when teaching IPv4 in college. Many of my former students will tell you that this approach makes the topic far easier — and far more enjoyable — to learn.
While I don’t assign “homework,” it’s incredibly valuable to practice these concepts, especially if you’re studying for a certification exam or working in a networking role. IPv4 shows up everywhere in the field, and you’ll eventually need to know these fundamentals by heart if you’re pursuing professional certifications from Cisco, Microsoft, Juniper, and others.
My hope is that you find this chapter easy to digest, whether you’re studying independently or following along with my videos. As always, feel free to share it with others — and I welcome any questions or comments.
— Jonathan Lincoln
