1:11 Lena: You mentioned that IPv4 has been around since the early 80s, which is wild to think about—it’s older than most of the apps we use! But when I look at a standard address like 192.168.1.10, I see four distinct numbers. How is that actually put together under the hood?
1:30 Miles: That’s the classic dotted decimal format. It looks simple to us, but for a computer, it’s all about binary. Each of those four numbers is called an octet. Why an octet? Because each one represents exactly eight bits of data. Since there are four octets, and each has eight bits, you get a total of 32 bits for the entire address.
1:51 Lena: So when I see a number like 192, the computer is actually seeing a string of ones and zeros?
1:57 Miles: Precisely. In the world of octets, each bit has a specific value based on its position—128, 64, 32, 16, 8, 4, 2, and 1. If you turn on the first two bits, 128 plus 64, you get 192. It’s like a set of eight light switches. If all the switches are off, the octet is zero. If they’re all on, you hit 255. That’s why you’ll never see an IP address with a number higher than 255 in any of the slots.
2:27 Lena: That makes so much sense! I’ve always wondered why 255 was the "magic number" in networking. So, we have these four octets, but they aren't all just identifying my specific device, right? I remember you saying something about neighborhoods earlier.
2:43 Miles: You’ve hit the nail on the head. Every IP address is split into two main parts: the network portion and the host portion. Think of the network portion as the name of your street or your zip code. It tells the routers out there which general area the data needs to go to. Then, the host portion is like your specific house number. It identifies your exact device within that network.
3:06 Lena: But how does the computer know where the "street" ends and the "house number" begins? If I just look at 192.168.1.10, it’s not obvious where the split is.
3:17 Miles: That is where the subnet mask comes into play. It’s the second required piece of the puzzle for any TCP/IP configuration. A subnet mask is also a 32-bit number, usually something like 255.255.255.0. When you line it up against the IP address, the ones in the mask hide the network part, and the zeros reveal the host part.
3:39 Lena: So if the mask is 255.255.255.0, that means the first three octets are the network?
0:32 Miles: Exactly. In binary, 255 is eight ones. So three octets of 255 means the first 24 bits are the network. In your example, 192.168.1 would be the network ID, and that last number, 10, is your host ID. If you changed the mask to 255.255.0.0, suddenly the network is just 192.168, and you have a lot more room for house numbers!
4:16 Lena: It’s like being able to resize the neighborhood based on how many houses you need to build. But wait—if we're changing the mask, does that mean the classes of networks I've heard about—Class A, B, and C—are still a thing?
4:28 Miles: It’s interesting how that evolved. Originally, the internet was strictly "classful." If your address started with a number between 1 and 126, you were Class A, meant for massive organizations with 16 million hosts. Class B was for medium networks, and Class C, which starts at 192, was for small ones with only 254 usable hosts. But that was really inefficient because if you needed 300 addresses, you had to take a Class B block and waste 64,000 of them!
4:56 Lena: That sounds like a huge waste of digital real estate.
4:59 Miles: It was! That’s why in 1993, we moved to CIDR—Classless Inter-Domain Routing. CIDR allows us to ignore those rigid class boundaries and use variable-length subnet masks. You’ll see it written with a slash, like /24. That’s just a shorthand way of saying "the first 24 bits are the network." It’s much more flexible and is really what kept IPv4 alive as long as it has.