- A
iptables -A INPUT -p tcp --dport 22 -j DROP
Why wrong: This would drop all SSH, contradicting the requirement.
- B
iptables -P INPUT DROP
Why wrong: This sets the default policy to drop, but it's a policy change, not a rule. The question asks for rules.
- C
iptables -A INPUT -j DROP
Why wrong: This would drop all incoming traffic, including established connections, unless placed after allow rules. But it's not strictly necessary if default policy is DROP.
- D
iptables -A INPUT -p tcp --dport 22 -s 10.0.0.0/8 -j ACCEPT
Allows SSH from the 10.0.0.0/8 network.
- E
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
Allows established connections.
Question 475 of 1,000
XK0-005 Security Practice Question
This XK0-005 practice question tests your understanding of security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 needs to configure iptables to allow incoming SSH traffic only from the 10.0.0.0/8 network and drop all other incoming traffic except established connections. Which TWO rules are necessary?
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 10.0.0.0/8 -j ACCEPT
Option D is correct because it explicitly allows incoming SSH traffic (TCP port 22) from the 10.0.0.0/8 network, which matches the requirement to permit SSH only from that subnet. Option E is correct because it accepts all packets that are part of an established or related connection, ensuring that return traffic for outbound connections is not dropped by the default policy or subsequent rules.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 -j DROP
Why it's wrong here
This would drop all SSH, contradicting the requirement.
- ✗
iptables -P INPUT DROP
Why it's wrong here
This sets the default policy to drop, but it's a policy change, not a rule. The question asks for rules.
- ✗
iptables -A INPUT -j DROP
Why it's wrong here
This would drop all incoming traffic, including established connections, unless placed after allow rules. But it's not strictly necessary if default policy is DROP.
- ✓
iptables -A INPUT -p tcp --dport 22 -s 10.0.0.0/8 -j ACCEPT
Why this is correct
Allows SSH from the 10.0.0.0/8 network.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
Why this is correct
Allows established connections.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often forget to include the rule for established connections (Option E) and mistakenly think setting a default DROP policy (Option B) or a blanket DROP rule (Option C) alone is sufficient, not realizing that without allowing established traffic, all return packets are dropped, breaking connectivity.
Detailed technical explanation
How to think about this question
The iptables connection tracking system uses the `state` module to classify packets as NEW, ESTABLISHED, RELATED, or INVALID. The rule `-m state --state ESTABLISHED,RELATED -j ACCEPT` ensures that packets belonging to an existing TCP session (e.g., SSH session responses) are accepted, even if the default policy is DROP. In a real-world scenario, failing to include this rule would cause outbound connections to fail because their return packets would be dropped, making the system unreachable for interactive sessions like SSH.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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
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FAQ
Questions learners often ask
What does this XK0-005 question test?
Security — This question tests Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: iptables -A INPUT -p tcp --dport 22 -s 10.0.0.0/8 -j ACCEPT — Option D is correct because it explicitly allows incoming SSH traffic (TCP port 22) from the 10.0.0.0/8 network, which matches the requirement to permit SSH only from that subnet. Option E is correct because it accepts all packets that are part of an established or related connection, ensuring that return traffic for outbound connections is not dropped by the default policy or subsequent rules.
What should I do if I get this XK0-005 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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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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