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Question 1,142 of 1,705

Network Security, Compliance and Governance →easyMultiple SelectObjective-mapped

Block Outbound Traffic to Malicious IPs with AWS Network Firewall

This ANS-C01 practice question tests your understanding of network security, compliance and governance. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

A security team needs to block outbound traffic from an EC2 instance to known malicious IP addresses while allowing all other outbound traffic. Which THREE steps should be taken? (Choose three.)

A
Configure network ACLs to deny outbound traffic to the malicious IPs.
Why wrong: Wrong: NACLs are stateless and not suitable for application-layer filtering.
B
Update the VPC route table to send traffic for the malicious IPs to a network firewall appliance.
Correct: Route traffic to firewall for inspection.
C
Deploy AWS Network Firewall in the VPC to perform stateful inspection.
Correct: AWS Network Firewall can block specific IPs.
D
Create a firewall rule in AWS Network Firewall that denies traffic to the malicious IPs.
Correct: The firewall rule denies traffic to listed IPs.
E
Modify the security group for the EC2 instance to deny outbound traffic to the malicious IPs.
Why wrong: Wrong: Security groups cannot block individual IPs in outbound rules; they allow/deny based on CIDR.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

Update the VPC route table to send traffic for the malicious IPs to a network firewall appliance.

The correct approach to block outbound traffic to known malicious IPs involves a combination of routing and stateful firewall inspection. Option B is correct because updating the VPC route table to send traffic for the malicious IPs to a network firewall appliance (e.g., AWS Network Firewall) enables centralized inspection and blocking. Option C is correct because deploying AWS Network Firewall provides stateful, application-layer inspection that can handle allow/deny rules for specific IPs. Option D is correct because a firewall rule within AWS Network Firewall can explicitly deny traffic to the malicious IPs. Option A is incorrect because network ACLs are stateless and require individual rules for each IP, making them impractical for dynamic blocklists. Option E is incorrect because security groups support only allow rules, not explicit deny; they cannot block specific IPs outbound.

Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
Configure network ACLs to deny outbound traffic to the malicious IPs.
Why it's wrong here
Wrong: NACLs are stateless and not suitable for application-layer filtering.
✓
Update the VPC route table to send traffic for the malicious IPs to a network firewall appliance.
Why this is correct
Correct: Route traffic to firewall for inspection.
Related concept
Standard ACLs match source addresses.
✓
Deploy AWS Network Firewall in the VPC to perform stateful inspection.
Why this is correct
Correct: AWS Network Firewall can block specific IPs.
Related concept
Standard ACLs match source addresses.
✓
Create a firewall rule in AWS Network Firewall that denies traffic to the malicious IPs.
Why this is correct
Correct: The firewall rule denies traffic to listed IPs.
Related concept
Standard ACLs match source addresses.
✗
Modify the security group for the EC2 instance to deny outbound traffic to the malicious IPs.
Why it's wrong here
Wrong: Security groups cannot block individual IPs in outbound rules; they allow/deny based on CIDR.

Common exam traps

Common exam trap: ACLs stop at the first match

ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.

Detailed technical explanation

How to think about this question

ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.

KKey Concepts to Remember

Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.

TExam Day Tips

Check inbound versus outbound direction.
Read the ACL from top to bottom.
Look for a broader permit or deny above the intended line.

Key takeaway

ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.

Real-world example

How this comes up in practice

A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.

What to study next

Got this wrong? Here's your next step.

Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related ANS-C01 ACL questions on filtering logic and placement.

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FAQ

Questions learners often ask

What does this ANS-C01 question test?

Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — Standard ACLs match source addresses..

What is the correct answer to this question?

The correct answer is: Update the VPC route table to send traffic for the malicious IPs to a network firewall appliance. — The correct approach to block outbound traffic to known malicious IPs involves a combination of routing and stateful firewall inspection. Option B is correct because updating the VPC route table to send traffic for the malicious IPs to a network firewall appliance (e.g., AWS Network Firewall) enables centralized inspection and blocking. Option C is correct because deploying AWS Network Firewall provides stateful, application-layer inspection that can handle allow/deny rules for specific IPs. Option D is correct because a firewall rule within AWS Network Firewall can explicitly deny traffic to the malicious IPs. Option A is incorrect because network ACLs are stateless and require individual rules for each IP, making them impractical for dynamic blocklists. Option E is incorrect because security groups support only allow rules, not explicit deny; they cannot block specific IPs outbound.

What should I do if I get this ANS-C01 question wrong?

What is the key concept behind this question?

Standard ACLs match source addresses.

About these practice questions

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Same concept, more angles

1 more ways this is tested on ANS-C01

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A company wants to block outgoing traffic from a specific EC2 instance to the internet, except for HTTPS traffic to a specific API endpoint. Which AWS service can enforce this at the instance level?

easy

A.AWS WAF
B.Network ACL
C.Security group with outbound rules
✓ D.AWS Network Firewall

Why D: Option D is correct because AWS Network Firewall can be deployed in the VPC to filter outbound traffic based on domain names. Option A (AWS WAF) is wrong because it works at the application layer for inbound web traffic and does not block outbound traffic at the instance level. Option B (Network ACL) is wrong because NACLs are stateless and work at the subnet level. Option C (Security group with outbound rules) is wrong because security groups do not support allowlisting based on domain names.

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