Before any of this is about AWS, it is about something much older and much simpler: getting a message from one machine to another.
A network is just machines that can reach each other, plus agreed rules about how. That is genuinely all. Everything else — subnets, route tables, gateways, firewalls — exists to answer two questions that turn out to be surprisingly hard at scale:
- Where is the machine I want?
- How does my message get there?
Why this section exists
Most AWS networking material opens with a diagram of a VPC — a big box, two smaller boxes labelled "public subnet" and "private subnet", arrows to an internet gateway. It looks explanatory and it is not, because you cannot understand why the boxes are that size, or why one is public, without understanding addressing first.
So the reader memorises the diagram. It works until something breaks, and then there is nothing underneath to reason from.
This course spends its first four sections on networking itself. AWS does not appear until section five. By then you will be able to look at 10.0.1.0/24 and know immediately how many addresses it holds, where it starts and ends, and whether it overlaps with 10.0.0.0/16 — and the VPC diagram will look obvious rather than arbitrary.
Two machines, one wire
Start with the simplest possible case: two computers connected by a cable. For one to send the other a message, three things must be true.
They must agree on how bits are represented — what voltage or light pulse means a one. That is the physical layer, and you will never think about it again in AWS.
They must be able to name each other. "Send this to that machine" needs a way to say which machine.
They must agree on how a message is packaged — where it starts, where it ends, how the receiver knows it arrived intact.
Now add a third machine, and a fourth, and eventually a few billion. Nothing conceptually changes; the naming problem simply becomes enormous. That problem is what IP addressing solves, and the next section is entirely about it.
If you have used AWS and found networking confusing, it is almost never the AWS part that is confusing. It is that the AWS part is a thin layer over ideas nobody taught you first. That is a content problem, not an aptitude one.