- A
iptables -A INPUT -p tcp --dport 22 -s 192.168.1.0/24 -j ACCEPT
Allows SSH from subnet.
- B
iptables -P OUTPUT ACCEPT
Sets default policy to accept outgoing.
- C
iptables -P FORWARD ACCEPT
Why wrong: Not needed; server is not a router.
- D
iptables -A INPUT -p tcp --dport 22 -j ACCEPT
Why wrong: This would allow SSH from any source, violating policy.
- E
iptables -P INPUT DROP
Sets default policy to drop incoming.
Question 754 of 1,000
XK0-005 Security Practice Question
This XK0-005 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.
An administrator is configuring iptables on a server. The requirements are: allow incoming SSH (port 22) from the 192.168.1.0/24 network, drop all other incoming traffic, and allow all outgoing traffic. Which three iptables rules achieve this? (Choose THREE.)
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
✓
iptables -A INPUT -p tcp --dport 22 -s 192.168.1.0/24 -j ACCEPT
Default policies: INPUT DROP, OUTPUT ACCEPT. Then allow SSH from subnet.
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.
- ✓
iptables -A INPUT -p tcp --dport 22 -s 192.168.1.0/24 -j ACCEPT
- ✓
iptables -P OUTPUT ACCEPT
Why this is correct
Sets default policy to accept outgoing.
Related concept
CIDR notation defines the prefix length.
- ✗
iptables -P FORWARD ACCEPT
Why it's wrong here
Not needed; server is not a router.
- ✗
iptables -A INPUT -p tcp --dport 22 -j ACCEPT
Why it's wrong here
This would allow SSH from any source, violating policy.
- ✓
iptables -P INPUT DROP
Why this is correct
Sets default policy to drop incoming.
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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
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 XK0-005 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this XK0-005 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: iptables -A INPUT -p tcp --dport 22 -s 192.168.1.0/24 -j ACCEPT — Default policies: INPUT DROP, OUTPUT ACCEPT. Then allow SSH from subnet.
What should I do if I get this XK0-005 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related XK0-005 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
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Last reviewed: Jul 4, 2026
This XK0-005 practice question is part of Courseiva's free CompTIA 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 XK0-005 exam.
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