ANS-C01 Network Security, Compliance and Governance Practice Question
Network Topology
Refer to the exhibit. A network engineer runs the above command and sees this network ACL configuration. The subnet associated with this ACL contains an EC2 instance that is failing to receive inbound HTTP traffic (TCP 80) from the internet. What is the MOST likely cause?
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
✓
The inbound deny rule for TCP (port range) blocks all TCP traffic
The inbound deny rule (Rule 100) for TCP (Protocol 6) from 0.0.0.0/0 denies all TCP traffic, including HTTP on port 80. Network ACLs evaluate rules in ascending order, so this deny rule is evaluated before any allow rules. Even though Rule 200 allows all traffic, the deny rule takes precedence because it comes first. Therefore, inbound HTTP traffic from the internet is blocked. Option A is incorrect because the subnet association does not affect the rule order; the deny rule applies to the subnet. Option C is incorrect because the outbound rule allows all traffic, so return traffic is not the issue. Option D is incorrect because the allow rule is wide enough (all traffic), but it is evaluated after the deny rule.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The inbound deny rule is associated with the wrong subnet
Why it's wrong here
The ACL is associated with the subnet, and the deny rule applies to all traffic from 0.0.0.0/0.
- ✓
The inbound deny rule for TCP (port range) blocks all TCP traffic
Why this is correct
Rule number 100 denies TCP traffic (protocol 6) from 0.0.0.0/0, which includes HTTP (TCP 80). The rule is evaluated before the allow rule.
- ✗
The outbound rule does not allow return traffic
Why it's wrong here
The outbound rule allows all traffic (protocol -1), so return traffic is allowed.
- ✗
The inbound allow rule is not wide enough
Why it's wrong here
The allow rule (Rule 200) allows all traffic, but it is never reached because the deny rule is evaluated first.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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