SCS-C03 Network Security Controls Guide

SCS-C03 network-security questions are about deciding which traffic should be allowed, which should be denied, and where that decision belongs. The exam usually wants you to separate instance-level admission, subnet-level stateless filtering, deeper inspection, hybrid secure connectivity, and deliberate segmentation.

What AWS is testing in this task

The current SCS-C03 domain page points to five recurring network patterns:

• choosing controls that permit or deny traffic correctly
• designing secure hybrid or multi-cloud connectivity
• meeting secure communication requirements between hybrid environments and AWS
• segmenting networks by security requirement
• finding and removing unnecessary access

That means this task is not just about opening or closing ports. It is about network intent and path control.

Network-control chooser

Security groups versus network ACLs

This is still one of the easiest places to lose points.

Use security groups when the question is about the workload’s allowed traffic.

Use network ACLs when the question is really about subnet-boundary stateless control.

If the requirement is deeper inspection, centralized rule logic, or network-layer threat policy, the best answer may be Network Firewall rather than either of those.

Hybrid security is more than “connect it”

SCS-C03 often turns a networking question into a security question by adding requirements such as:

• encryption on the path
• controlled access from external or partner environments
• specific workload communication requirements
• reduced trust in network location alone

That is where secure VPN design, Direct Connect plus MACsec where relevant, or Verified Access can become the stronger answer.

Segmentation is a prevention control

Good segmentation answers usually:

• separate workloads by trust boundary
• reduce east-west movement
• place inspection where it matters
• avoid flat networks with broad internal reachability

The exam usually rewards the answer that reduces unnecessary communication rather than only logging it.

Unnecessary access should be removed, not just observed

AWS explicitly includes identifying unnecessary access. That means the best answer often does more than “monitor the path.”

It may:

• remove exposed routes
• tighten security group rules
• segment a shared subnet design
• use analysis tooling to prove the path is unnecessary and then close it

If the answer notices bad reachability but leaves it open, it is usually not the strongest control answer.

Common traps

• using security groups when the requirement is centralized inspection
• choosing “encrypted hybrid connectivity” when the core problem is still over-broad reachability
• leaving east-west paths open because north-south filtering looks correct
• treating network location as sufficient identity for application access
• detecting unnecessary access but not actually removing it

Fast decision rule

When the problem is which traffic should exist at all, decide first whether the control belongs at the workload, subnet, inspection plane, hybrid path, or segmentation layer.

Quiz

Continue to 4. Identity and Access Management once you can separate network path control from identity and authorization control.