Question 269 of 997

Security →mediumMultiple SelectObjective-mapped

CV0-004 Security Practice Question

This CV0-004 practice question tests your understanding of security. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 cloud administrator is configuring network ACLs (NACLs) for a VPC subnet. The subnet hosts a web server that must accept HTTP (port 80) and HTTPS (port 443) from the internet, and the server needs to respond to clients. Which TWO rules are required?

A
Inbound rule: allow all ICMP from 0.0.0.0/0
Why wrong: ICMP is not required for HTTP/HTTPS.
B
Outbound rule: allow TCP port 80 and 443 to 0.0.0.0/0
Why wrong: Outbound HTTP/HTTPS would be for outbound requests, not responses.
C
Inbound rule: allow TCP ports 1024-65535 from 0.0.0.0/0
Why wrong: Inbound ephemeral ports are not needed for web server.
D
Outbound rule: allow TCP ports 1024-65535 to 0.0.0.0/0
Allows return traffic on ephemeral ports.
E
Inbound rule: allow TCP port 80 and 443 from 0.0.0.0/0
Allows incoming web traffic.

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

✓

Outbound rule: allow TCP ports 1024-65535 to 0.0.0.0/0

NACLs are stateless, so both inbound and outbound rules must be explicitly allowed. Inbound allows HTTP/HTTPS, outbound allows ephemeral ports for return traffic.

Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

Answer analysis

Option-by-option breakdown

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

✗
Inbound rule: allow all ICMP from 0.0.0.0/0
Why it's wrong here
ICMP is not required for HTTP/HTTPS.
✗
Outbound rule: allow TCP port 80 and 443 to 0.0.0.0/0
Why it's wrong here
Outbound HTTP/HTTPS would be for outbound requests, not responses.
✗
Inbound rule: allow TCP ports 1024-65535 from 0.0.0.0/0
Why it's wrong here
Inbound ephemeral ports are not needed for web server.
✓
Outbound rule: allow TCP ports 1024-65535 to 0.0.0.0/0
Why this is correct
Allows return traffic on ephemeral ports.
Related concept
CIDR notation defines the prefix length.
✓
Inbound rule: allow TCP port 80 and 443 from 0.0.0.0/0
Why this is correct
Allows incoming web traffic.
Related concept
CIDR notation defines the prefix length.

Common exam traps

Common exam trap: usable hosts are not the same as total addresses

Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.

Detailed technical explanation

How to think about this question

Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.

KKey Concepts to Remember

CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.

TExam Day Tips

Write the block size before choosing the subnet.
Check whether the question asks for hosts, subnets or a specific address range.
Do not confuse /24, /25, /26 and /27 host counts.

Key takeaway

Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

Real-world example

How this comes up in practice

A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.

Visual reference

What to study next

Got this wrong? Here's your next step.

Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related CV0-004 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this CV0-004 question test?

Security — This question tests Security — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: Outbound rule: allow TCP ports 1024-65535 to 0.0.0.0/0 — NACLs are stateless, so both inbound and outbound rules must be explicitly allowed. Inbound allows HTTP/HTTPS, outbound allows ephemeral ports for return traffic.

What should I do if I get this CV0-004 question wrong?

What is the key concept behind this question?

CIDR notation defines the prefix length.

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Last reviewed: Jul 4, 2026

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