The correct answer is that SSH and ICMP echo-request are allowed while all other traffic is dropped. This is because the firewall rules explicitly permit TCP port 22 for SSH and ICMP type 8 for echo-request (ping), while the final rule is a default deny that drops any packet not matching those two exceptions. On the CompTIA Linux+ XK0-005 exam, this scenario tests your ability to read iptables or nftables rule order and understand that a default drop policy overrides any implicit allowances—a common trap is assuming loopback or established traffic is permitted without an explicit rule. To remember the effect of firewall rules allowing SSH and ICMP echo-request, think of the mnemonic “SSH and Ping, then the Drop brings the sting.”
XK0-005 Security Practice Question
This XK0-005 practice question tests your understanding of security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
SSH and ICMP echo-request are allowed; all other traffic is dropped.
The firewall rules shown explicitly allow SSH (port 22) and ICMP echo-request (type 8) traffic while the final default rule drops all other traffic. This matches option D, as the rules do not permit any other protocols or services, including loopback traffic unless it is SSH or ICMP echo-request.
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.
✗
Only SSH traffic to 192.168.1.10 is allowed; all other traffic is dropped.
All traffic on eth0 is allowed; loopback is allowed.
Why it's wrong here
Only specific traffic on eth0 is allowed; default policy drops the rest.
✓
SSH and ICMP echo-request are allowed; all other traffic is dropped.
Why this is correct
The rules allow SSH, ICMP echo-request, and loopback; default drop handles the rest.
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 assume loopback traffic is implicitly allowed or that the rules apply to all interfaces, but the rules only apply to the INPUT chain on eth0 and do not include any explicit loopback allowance, so only the specified protocols are permitted.
Detailed technical explanation
How to think about this question
In iptables, rules are processed in order, and the first match determines the action. The rules shown use '-A INPUT' to append to the INPUT chain, with '-p tcp --dport 22 -j ACCEPT' for SSH and '-p icmp --icmp-type echo-request -j ACCEPT' for ICMP echo-request. The final rule '-j DROP' acts as a default deny policy, dropping any packet that does not match the preceding allow rules. This is a common security practice to whitelist only necessary services.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this XK0-005 question in full detail.
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: SSH and ICMP echo-request are allowed; all other traffic is dropped. — The firewall rules shown explicitly allow SSH (port 22) and ICMP echo-request (type 8) traffic while the final default rule drops all other traffic. This matches option D, as the rules do not permit any other protocols or services, including loopback traffic unless it is SSH or ICMP echo-request.
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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Question Discussion
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