Cloud Networking Basics: VPCs, Subnets, and How Traffic Actually Flows

Cloud networking is one of those areas people skip past, configure once by copying a tutorial, and never really understand, which is unfortunate, because how your cloud network is built is one of the biggest factors in how secure you are. The good news is the core concepts are not complicated. Once you understand a handful of building blocks, the whole thing makes sense. Here they are.

The core building blocks

VPC (Virtual Private Cloud). Your own private, isolated section of the cloud provider's network. Think of it as your own walled space within the larger cloud, where your resources live and where you control how traffic moves. Everything else is organized inside it.

Subnets. Subdivisions within your VPC. You split your network into smaller segments, typically separating things that should be reachable from the internet (public subnets) from things that shouldn't be (private subnets). For example, a public-facing web server might sit in a public subnet, while your database sits in a private subnet where the internet can't reach it directly.

Security groups and network rules. These control what traffic is allowed where. They act like firewalls around your resources, defining which connections are permitted and which are blocked. This is where you decide, very specifically, who can talk to what.

Gateways and routing. These control how traffic flows in and out of your network and between its parts, the paths traffic is allowed to take.

Put together: a VPC is your private space, subnets divide it into zones with different exposure, security rules control what's allowed to communicate, and gateways and routing govern the flow.

Why this matters more than it looks

These aren't just technical plumbing decisions. How you design your network determines your exposure. A few examples:

• Put a database in a public subnet by mistake, and you've exposed it to the internet. This exact error is behind countless breaches.
• Leave security group rules too open, and you've invited traffic you didn't intend.
• Fail to separate your network into zones, and a breach in one place can reach everything.

Good cloud networking is, in large part, good security. The network is where you decide what can reach what, which is the foundation of containing damage when something goes wrong.

The principle that should guide it

There's a simple rule that prevents most network security problems: allow only what's necessary, and isolate everything else.

In practice:

• Private by default. Don't expose anything to the internet unless it genuinely needs to be. Databases, internal services, and sensitive systems belong in private subnets.
• Segment your network. Divide it into zones so that a breach in one area can't freely reach the rest. Containment is as important as prevention.
• Least-privilege traffic rules. Allow only the specific connections that are needed, and block the rest by default. Open rules "to make it work" are how exposure creeps in.
• Control and inspect the flow. Know what's allowed to talk to what, and watch for anything unexpected.

Where this leads

If you've read our other pieces, this principle should sound familiar: allow only what's necessary, isolate everything, verify rather than assume, and contain damage by segmentation. That's Zero Trust, and cloud networking is one of the places it lives most concretely. Your network design is one of the clearest expressions of whether you've adopted a verify-everything, least-access posture or a loose, "inside is trusted" one.

The reason this matters: network configuration is something organizations often get partly right and partly wrong, leaving exactly the gaps attackers look for. One overly open security group, one resource in the wrong subnet, one segment that should have been isolated. A coherent approach, applying the same least-access, segment-everything discipline consistently across the whole network, is what removes those gaps. Piecemeal configuration leaves them.

How Mars Innovation approaches it

We design and secure your cloud network as part of a coherent, verify-everything posture, not a patchwork of rules:

• Zero Trust Launchpad brings proper network segmentation, least-privilege traffic control, private-by-default design, and continuous inspection to your cloud environment, closing the configuration gaps where breaches actually start.

A well-designed network is most of your security. We make sure yours is built right. Every engagement is fixed-price, with scope and cost known up front.

The takeaway

Cloud networking comes down to a few building blocks: a VPC for your private space, subnets to divide it into zones of different exposure, security rules to control what can talk to what, and gateways to govern the flow. How you design it is largely a security decision, and the guiding principle is to allow only what's necessary and isolate everything else, applied consistently. That consistency, real Zero Trust networking, is what closes the gaps attackers exploit.

Not confident your cloud network is closed where it should be?

We'll design and secure it with consistent segmentation and least-access control.

→ Explore the Zero Trust Launchpad — fixed-price, scoped, and built to close the gaps.