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SOA-C02 Networking and Content Delivery Practice Question

Network Topology
$ aws ec2 describe-network-aclsregion us-east-1Refer to the exhibit.```"NetworkAcls": ["NetworkAclId": "acl-12345678","VpcId": "vpc-12345678","DefaultNetworkAcl": false,"Entries": ["RuleNumber": 100,"Protocol": "6","PortRange": {"From": 443,"To": 443},"RuleAction": "allow","Egress": false,"CidrBlock": "0.0.0.0/0""RuleNumber": 200,"Protocol": "-1","From": 0,"To": 65535"Egress": true,"RuleNumber": 300,"From": 80,"To": 80"RuleNumber": 400,"RuleAction": "deny",

An EC2 instance in the subnet associated with the network ACL above cannot receive HTTP traffic (port 80) from the internet. The instance has a security group allowing HTTP inbound. What is the 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 NACL has a deny all rule (rule 400) that blocks all inbound traffic, overriding the allow rules

Network ACLs are stateless and rules are evaluated in order by rule number. Rule 400 denies all inbound traffic, and since it has a higher rule number than rules 100 and 300, it is evaluated later and overrides the allows. Rule 400 denies all inbound traffic, so HTTP (port 80) is denied. Option A is wrong because rule 300 allows port 80 inbound from 0.0.0.0/0, so HTTP is allowed by that rule, but rule 400 denies all. Option B is wrong because the outbound rule allows all traffic. Option D is wrong because the security group allows HTTP inbound but the NACL blocks it.

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 NACL allows HTTP inbound on rule 300, but the outbound rule does not allow the return traffic

    Why it's wrong here

    Outbound allows all traffic, so return traffic is allowed.

  • ✗

    The NACL inbound rule for HTTP is using the wrong protocol (6 instead of 17)

    Why it's wrong here

    Protocol 6 is TCP, which is correct for HTTP.

  • ✓

    The NACL has a deny all rule (rule 400) that blocks all inbound traffic, overriding the allow rules

    Why this is correct

    Rule 400 denies all inbound traffic, so even though rule 300 allows HTTP, it is overridden.

  • ✗

    The security group does not allow HTTP inbound

    Why it's wrong here

    The stem states the security group allows HTTP inbound.

Visual reference

Source Router + ACL permit 10.0.0.0/8 deny any Server 10.0.0.5 ✓ 192.168.1.1 ✗ dropped ACLs evaluate top-down; first match wins — implicit deny all at end

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JA

Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

This SOA-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SOA-C02 exam.