When I started studying for CCNA, VLANs and subnetting felt like abstract concepts — things you learn for the exam. Then I started working on AWS VPC design, and suddenly they made perfect sense. The two disciplines are deeply connected.
What is a VLAN?
A VLAN (Virtual Local Area Network) lets you segment a physical network into multiple logical networks. Devices on different VLANs can’t communicate directly — they need a router (or layer 3 switch) to pass traffic between them. This gives you isolation without physically separating hardware.
In a traditional office network, you might put finance on VLAN 10, HR on VLAN 20, and general staff on VLAN 30. A compromised device on the staff VLAN can’t directly access finance systems — the VLAN boundary stops it.
Subnetting: dividing IP space logically
Subnetting is how you divide an IP address range into smaller, manageable blocks. A /24 subnet gives you 256 addresses. A /26 gives you 64. Choosing the right subnet size means you don’t waste address space, and you can route traffic precisely where it needs to go.
For our AWS VPC project, I used a 10.0.0.0/16 range for the whole VPC, then carved out /24 subnets for each availability zone — 10.0.1.0/24 for public subnet 1, 10.0.2.0/24 for public subnet 2, 10.0.11.0/24 for private subnet 1, and so on.
How this maps to AWS
AWS subnets are the cloud equivalent of VLANs. A public subnet with an Internet Gateway attached behaves like a VLAN with external routing. A private subnet with no internet route behaves like an isolated VLAN. The concepts are the same — the implementation is just managed by AWS instead of a physical switch.
Understanding subnetting made me much faster at VPC design. Instead of guessing at CIDR blocks, I could plan the address space deliberately — reserving room for growth, keeping public and private ranges clearly separated, and making the architecture readable to anyone who looked at it.
The lesson
CCNA knowledge isn’t wasted in a cloud role — it’s foundational to it. The better you understand how traditional networks work, the better you’ll design cloud networks. AWS, Azure, and GCP all implement the same core networking concepts, just with different interfaces on top.